JP2004106175A - Impact tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an impact tool which exerts strong fastening force, is reduced in size and weight, and restrains noise. <P>SOLUTION: This impact tool comprises: a drive part 1; a drive shaft 13 rotated and driven by the drive part 1, a hammer 21 fitted slidably to the drive shaft 13 via a cam mechanism 10 to perform rotating motion together with the drive shaft 13; an anvil 31 for performing rotating motion through engagement with the hammer 21; an urging means 9 for urging the hammer 21 to the anvil 31 side; and a bit 35 coupled to the anvil 31. The impact tool repeatedly performs engagement between the hammer 21 and the anvil 31 as an impact by the cam mechanism 10. An impact frequency to the anvil 31 by the hammer 21 is made to correspond to a natural frequency of a torsional vibration system 3b comprising of the anvil 31, the bit 35, and a screw 4 coupled to the bit 35, or an integral multiple more than 2 of the natural frequency, or reciprocal multiple of number of an integer 2 or more of the natural frequency. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an impact tool, and more particularly, to a technique for amplifying a rotational torque applied to an anvil by hitting of a hammer by using a natural frequency of a torsional vibration system.

FIG. 12 shows the internal structure of a conventional impact tool. The drive unit 1 includes a motor 11 and a speed reducer 12. A drive shaft 13 protrudes from the speed reducer 12, and the drive shaft 13 is rotated by an output of the motor 11 transmitted through the speed reducer 12. It has become. A substantially cylindrical hammer 21 is axially slidably fitted to the distal end of the drive shaft 13 via the cam mechanism 10, and the hammer 21 rotates together with the drive shaft 13. . The cam mechanism 10 is fitted between a cam groove 14 formed on the outer peripheral surface of the distal end portion of the drive shaft 13, a hammer cam groove 24 formed on the inner peripheral surface of the hammer 21, and the opposed cam grooves 14, 24. And a steel ball 23 connecting the drive shaft 13 and the hammer 21. A spring 27 is interposed between the drive unit 1 and the hammer 21 as urging means 9 for urging the hammer 21 toward an anvil 31 described later. An anvil 31 is rotatably mounted on an extension of the center axis of the drive shaft 13 and opposite to the drive unit 1 with the hammer 21 therebetween. At the rear end side of the anvil 31 (opposite side to the hammer 21), a pair of struck arms 32 is extended in the radial direction, and at the front end side of the hammer 21 (opposite side to the anvil 31), an axial direction is provided. A pair of striking projections 25 are provided, and the struck arm 32 and the striking projection 25 are engaged with each other so that the anvil 31 rotates integrally with the hammer 21. A bit 35 is connected to the tip of the anvil 31 so that the bit 35 can be freely inserted and removed and performs a rotational movement integrally.

In the impact tool having the above structure, the output of the drive unit 1 is transmitted to the drive shaft 13, the hammer 21, the anvil 31, and the bit 35 to perform a tightening operation such as a screw tightening operation. When a certain load or more is applied to the motor and the rotation is slowed down, a component force is generated via the cam mechanism 10 to push down the hammer 21 against the urging force of the spring 27, and the engagement between the hammer 21 and the anvil 31 is generated. Then, the hammer 21 is shockably engaged with the anvil 31 while rotating with respect to the anvil 31 by the restoring force of the spring 27. As described above, when a certain load or more is generated during work such as screw tightening, the above-described impactful engagement (that is, hitting) in the rotational direction is repeated to generate a strong rotational torque. It is.

In the conventional impact tool described above, in order to obtain a large rotational torque, it is necessary to increase the moment of inertia of the hammer 21 or to increase the rotational speed of the drive shaft 13. As a result, the overall size and impact of the impact tool are increased. It was causing weight increase. For this reason, especially for middle-aged and elderly workers, there is a problem that the work load is reduced because the burden on the arm is increased. In addition, since the drive shaft 13 is rotated at a high speed, the impact tool, which originally has a large noise, generates more noise. There is a problem in that it may cause an adverse effect on workers and neighborhoods.

On the other hand, for example, a clutch spring is interposed between the hammer 21 and the anvil 31, and the rotational motion is transmitted via the clutch spring, thereby solving the problem of noise generation due to impact. Although a tool has been proposed (see Patent Document 1), in order to obtain a large rotating torque, it is necessary to increase the size and weight of the entire impact tool. It was not able to exert a gentle force.
JP-A-10-166278

The present invention has been made in view of the above points, and has as its object to provide an impact tool which exerts a strong tightening / closing force, is small and lightweight, and has reduced noise.

In order to solve the above-mentioned problem, the present invention relates to a driving unit 1, a driving shaft 13 rotatably driven by the driving unit 1, and slidably fitted to the driving shaft 13 via a cam mechanism 10 to rotate together. A hammer 21 to perform, an anvil 31 that performs a rotational motion by engagement with the hammer 21, an urging means 9 for urging the hammer 21 toward the anvil 31, and a bit 35 connected to the anvil 31; In the impact tool which repeatedly engages the hammer 21 and the anvil 31 as a hit by the cam mechanism 10, the impact frequency of the hammer 21 to the anvil 31 is determined by the natural frequency of the torsional vibration system 3 including the anvil 31 and the bit 35, Alternatively, the characteristic frequency is made to match an integral multiple of 2 or more of the natural frequency or a reciprocal multiple of an integer of 2 or more of the natural frequency.

This makes it possible to effectively amplify the rotational torque caused by the impact of the hammer 21 by utilizing the resonance phenomenon in the torsional vibration system 3, thereby reducing the size of the impact tool that exerts a strong tightening force. Since it can be provided with light weight and low noise, it is possible to reduce the fatigue of the operator and to reduce the influence on the surroundings. In particular, when the impact frequency matches the natural frequency, the rotational torque can be amplified most effectively, and when it matches an integer multiple of 2 or more of the natural frequency, the working time is greatly reduced. When the frequency is made to be equal to the reciprocal multiple of an integer of 2 or more of the natural frequency, high quietness can be obtained.

In order to solve the above-mentioned problem, the present invention relates to a driving unit 1, a driving shaft 13 that is driven to rotate by the driving unit 1, a hammer 21 that rotates together with the driving shaft 13 while being connected to the driving shaft 13, An anvil 31 rotatably provided on the inner or outer peripheral side of the anvil 21, and a bit 35 which rotates together with the anvil 31 while being connected to the anvil 31. A magnetic pole portion 41 is disposed on one of the opposing portions of the hammer 21, and a magnetic body 42 is disposed on the other of the opposing portions of the hammer 21 by magnetic attraction generated between the magnetic pole portion 41 and the magnetic body 42. In the impact tool for applying a non-contact impact to the anvil 31 in accordance with the rotational motion of the torsion vibration system 3 including the anvil 31 and the bit 35, the impact frequency of the hammer 21 to the anvil 31 is changed. Natural frequency or more integral multiple of said intrinsic vibration frequency or the reciprocal of an integer of 2 or more of said intrinsic vibration frequency, may be obtained by, characterized in that match.

By doing so, in addition to generating no noise such as a direct hit when generating a hitting force, the rotational torque due to the hitting of the hammer 21 by utilizing the resonance phenomenon in the torsional vibration system 3 is effective. It will be amplified to exhibit a powerful tightening force. As a result, it is possible to provide an impact tool exhibiting a strong tightening force with a small size, light weight and low noise, to reduce the fatigue of the worker, and to reduce the influence on the surroundings. Become. In particular, when the impact frequency matches the natural frequency, the rotational torque can be amplified most effectively, and when it matches an integer multiple of 2 or more of the natural frequency, the working time is greatly reduced. When the frequency is made to be equal to the reciprocal multiple of an integer of 2 or more of the natural frequency, high quietness can be obtained.

In each of the impact tools described above, it is preferable that the torsional vibration system 3 includes the screw 4 connected to the bit 35. In this way, the screw tightening operation and the nut tightening operation in the seated state are performed. In addition to the above, even in the screw tightening and loosening operation in the non-seated state, the rotational torque caused by the impact of the hammer 21 can be effectively amplified by utilizing the resonance phenomenon in the torsional vibration system 3.

Further, a natural frequency detecting means A for detecting a natural frequency of the torsional vibration system 3, a striking frequency changing means B for changing a striking frequency of the hammer 21 to the anvil 31, and a natural frequency obtained by the natural frequency detecting means A Torque automatic amplifying means C for automatically controlling the striking frequency changing means B so that the striking frequency coincides with the vibration frequency or an integral multiple of two or more of the natural frequency or a reciprocal multiple of an integer of two or more of the natural frequency. It is also preferable that the tightening operation is always performed with a large rotating torque without the operator having to make adjustments by himself.

In addition, as the natural frequency detecting means A of the torsional vibration system 3, a natural angle is obtained from a rotational angle sensor 5a for detecting the rotational angle of the anvil 31 or the bit 35 and a vibration component between impacts of the rotational angle obtained from the rotational angle sensor 5a. It is also preferable to include a calculation unit 7 for calculating the number. In this way, a means for detecting the natural frequency can be configured at relatively low cost.

In addition, as the natural frequency detecting means A of the torsional vibration system 3, a rotation speed sensor 5b for detecting the rotation speed of the anvil 31 or the bit 35, and a rotation angle obtained by integrating the rotation speed obtained from the rotation speed sensor 5b are obtained. It is also preferable to provide a calculation unit 7 for calculating the natural frequency from the vibration component between the impacts of the rotation angle. In this way, the means for detecting the natural frequency can be configured relatively inexpensively. Can be.

Further, as the natural frequency detecting means A of the torsional vibration system 3, a rotational acceleration sensor 5c for detecting a rotational acceleration of the anvil 31 or the bit 35, and a rotational acceleration obtained from the rotational acceleration sensor 5c are double-integrated to obtain a rotational angle. It is also preferable to provide a calculation unit 7 for calculating the natural frequency from the vibration component between the impacts of the rotation angle and the impact. Contribute to improvement.

Further, as the natural frequency detecting means A of the torsional vibration system 3, a natural torque is obtained from a rotational torque sensor 5d for detecting a rotational torque of the anvil 31 or the bit 35, and a vibration component between impacts of the rotational torque obtained from the rotational torque sensor 5d. It is also preferable to provide a calculation unit 7 for calculating the number. In this way, the impact force can be grasped numerically, thereby contributing to the management of the rotational torque and the improvement of accuracy.

It is also preferable to have an initial natural frequency detection mode in which the anvil 31 is rotated for a short time during which no impact occurs and the natural frequency detecting means A detects an initial value of the natural frequency of the torsional vibration system 3. By doing so, a rotational torque corresponding to the initial natural frequency is given at the first impact, and the tightening operation is performed with a large rotational torque from the beginning, thereby improving the work efficiency.

Further, a memory section 8 which records the natural frequency obtained by the natural frequency detecting means A with time in the torque automatic amplifying means C, and a predicted value of the natural frequency based on the natural frequency recorded in the memory section 8 It is also preferable to include a predicted value calculating unit 23 for calculating p. In this way, the natural frequency at the next impact can be predicted based on the temporal change of the natural frequency, and the peak can be further improved. The rotational torque can be amplified to a value close to the value, and the working efficiency can be improved.

Further, the predicted value calculating section 23 compares the past natural frequency at the time of screw tightening and loosening recorded in the memory section 8 with the predicted value p of the natural frequency at another screw tightening and loosening after the screw tightening and loosening. It is also preferable to use it for the calculation. In this way, when the screw tightening and loosening operation using the same kind of screw 4 is continuously performed, the striking frequency can be accurately matched with the natural frequency from the initial stage. It is possible to improve the work efficiency each time the work is repeated.

In addition, the predicted value calculating unit 23 corrects the past natural frequency at the time of screw tightening and loosening recorded in the memory unit 8 by the natural frequency detected at the current screw tightening and loosening, and corrects the current screw tightening and loosening. It is also preferable to use the predicted value p of the natural frequency in the work, and by doing so, it is possible to suppress the influence of subtle variations that occur each time the screw tightening work is loosened.

The parameters characterizing the screw 4 used are recorded in the memory unit 8 together with the natural frequency, and the next time the screw is tightened and loosened, the natural frequency corresponding to the input of each parameter is used to record the natural frequency. It is also preferable to include parameter input means D for calculating the predicted value p. In this way, even if the tightening work is not continuously performed on the screws 4 of the same type, the past natural vibration The natural frequency can be predicted using the number data.

It is also preferable to form the drive unit 1 with a motor 11 and a speed reducer 12, and to provide a drive circuit 17 for changing the number of revolutions of the motor 11 as the impact frequency changing means B. Can be adjusted to accommodate screws 4 of various lengths and materials.

It is also preferable to form the drive unit 1 by a motor 11 and a continuously variable speed reducer 12, and to provide a drive circuit 17 for changing the reduction ratio of the speed reducer 12 as the striking frequency changing means B. This makes it possible to adjust the impact frequency while maintaining the rotational speed of the motor 11 at the rotational speed with the highest energy conversion efficiency, so that the power consumption can be reduced. The number of screws 4 that can be tightened can be increased.

According to the present invention, it is possible to amplify the rotational torque due to the impact of the hammer by utilizing the resonance phenomenon in the torsional vibration system, thereby making it possible to reduce the impact tool exerting a strong tightening force with a small size, light weight and low noise. Since it can be provided by a product, there is an effect that the fatigue of the worker can be reduced and the influence on the surroundings can be reduced.

Hereinafter, the present invention will be described based on embodiments shown in the accompanying drawings. Note that the same components as those shown in the related art are denoted by the same reference numerals and description thereof will be omitted, and the characteristic features of the present invention will be described in detail by adding new symbols.

FIG. 1 shows an example of an impact tool according to the embodiment of the present invention. In the impact tool, a torsion vibration system 3, which will be described later, repeatedly tightens or loosens a screw 4, a nut (not shown), and the like by being hit in the rotational direction by a hammer 21. The torsional vibration system 3 can be considered as comprising the anvil 31 and the bit 35 when the screw is tightened or loosened in the seated state (hereinafter, referred to as the torsional vibration system 3a in this case). When the screw is tightened and loosened in the seated state, the torsional vibration system 3 can be considered to be formed by the anvil 31, the bit 35, and the screw 4 connected to the bit 35 (hereinafter, in this case, the torsion). The vibration system 3b). The shaft portion 31a of the anvil 31 is formed with a constriction in order to reduce the natural frequency of the entire torsional vibration system 3.

In each of the torsional vibration systems 3a and 3b, by making the natural frequency of the entire system coincide with the striking frequency of the hammer 21 on the anvil 31, the rotational torque given by the hammer 21 is amplified, thereby reducing the size and weight. A strong tightening force can be exerted even with impact tools. In addition, since it is not necessary to rotate the drive shaft 13 at high speed, noise is suppressed.

Since the rotational torque required for the screw tightening and loosening operation in the non-seated state is much smaller than the rotational torque required for the screw tightening and loosening operation in the seated state, the torsional vibration system 3 generally includes the anvil 31 and the bit 35. The torsional vibration system 3a may be designed so that the impact frequency and the natural frequency match as described above. However, when a large rotational torque is required even in the screw tightening and loosening process in the non-seated state, the torsional vibration system 3 is regarded as a torsional vibration system 3 b including the anvil 31, the bit 35 and the screw 4, and the impact is applied. It is preferable to make the frequency and the natural frequency coincide. In this case, for example, from the start of screw tightening to the seating, the amount of protrusion of the screw 4 from the workpiece 6 gradually decreases (see FIG. 4A), and the natural frequency gradually increases accordingly. Since it becomes larger, it is necessary to change the striking frequency in accordance with the change in the natural frequency.

Therefore, in the present embodiment, a natural frequency detecting means A for detecting the natural frequency of the torsional vibration system 3b, a hitting frequency changing means B for changing the hitting frequency of the hammer 21 to the anvil 31, and a natural frequency detecting means A torque automatic amplifying means C for automatically controlling the striking frequency changing means B so that the natural frequency obtained in A and the striking frequency coincide with each other is provided.

Specifically, a rotation angle sensor 5a for measuring the rotation angle of the anvil 31 is provided around the anvil 31 as the natural frequency detecting means A, and the rotation angle sensor 5a is connected to the arithmetic processing unit 15 by a signal line 14. Connected. The arithmetic processing unit 15 includes an arithmetic unit 7 that calculates a natural frequency from a vibration component between hits of the rotation angle obtained from the rotation angle sensor 5a, and the RAM unit 19 and the ROM unit 20 through a signal line 22. The time variation of the rotation angle of the anvil 31 detected by the rotation angle sensor 5a during the work is taken into the RAM unit 19, and the natural frequency is detected by the arithmetic unit 7 based on the time variation. It has become. Generally, as shown in FIG. 2, the rotation angle increases stepwise with each impact, but immediately after the impact, micro-vibration is generated by the torsional vibration component of the torsional vibration system 3b. Is analyzed, the natural frequency can be detected. Further, the rotation angle sensor 5a is provided to measure the rotation angle of the bit 35, and the natural frequency of the torsional vibration system 3b can be detected by the same configuration.

A rotation speed sensor 5b for detecting the rotation speed of the anvil 31 or the bit 35 is provided instead of the rotation angle sensor 5a, and the calculation unit 7 integrates the rotation speed obtained from the rotation speed sensor 5b to obtain the rotation angle. In addition, a natural frequency may be detected from a vibration component between impacts of the rotation angle, or a rotation acceleration sensor 5c for detecting the rotation acceleration of the anvil 31 or the bit 35 is provided instead of the rotation angle sensor 5a. The arithmetic unit 7 may double-integrate the rotational acceleration obtained from the rotational acceleration sensor 5c to obtain the rotational angle, and calculate the natural frequency from the vibration component between the impacts of the rotational angle. Instead of the rotation angle sensor 5a, a rotation torque sensor 5d for detecting the rotation torque of the anvil 31 or the bit 35 is provided. That from the vibration component between striking as shown in Figure 3 of the torque may be calculated natural frequency.

駆 動 As the impact frequency changing means B, a drive circuit 17 connected to the drive unit 1 via a drive line 16 is provided. The drive circuit 17 controls the rotation speed of the motor 11 to be a desired rotation speed, and the output from the drive unit 1 to the drive shaft 13 can be freely changed by the above control. When the speed reducer 12 constituting the drive unit 1 is a continuously variable transmission, the drive circuit 17 allows the speed reducer 12 to be freely changed to a desired speed reduction ratio by an actuator (not shown). The output from 1 to the drive shaft 13 may be changed freely. In this case, there is an advantage that the motor 11 can be maintained at a highly efficient rotation speed.

The torque automatic amplifying means C is constituted by the arithmetic processing unit 15. The arithmetic processing unit 15 drives the control circuit via the signal line 18 so as to perform control such that the striking frequency matches the natural frequency based on the natural frequency obtained from the detection result of the rotation angle sensor 5a and the like. 17 is sent. The arithmetic processing unit 15, the drive circuit 17, and the memory unit 8 form a control unit 2 that automatically controls the drive unit 1 so that the hitting frequency of the next hitting matches the natural frequency.

Here, in order to more effectively match the natural frequency with the striking frequency, the change in the natural frequency after the start of striking recorded in the RAM unit 19 of the memory unit 8 with time is calculated. 4B approximates a simple curve as shown by a dotted line in FIG. 4B, and calculates a predicted value p of the natural frequency at the time of the next impact from the approximated curve. The driving unit 1 is preferably controlled based on the value p such that the impact frequency of the next impact matches the natural frequency.

初期 In addition, it is preferable that an initial natural vibration detection mode is provided for cases where a large rotation torque is required from the start of screwing. In this mode, the anvil 31 is first rotated for a short period of time during which no impact occurs, and then stopped, so that the rotation frequency can be calculated from the minute vibration generated in the output value of the rotation angle sensor 5a and the like. It is possible to apply a large rotating torque to the hammer 21 from the second hit.

When the output to the drive shaft 13 is changed by changing the reduction ratio of the speed reducer 12 as described above, the observed natural frequency obtained from the rotation angle sensor 5a or the like as shown in FIG. A large gap G is produced between the solid line (solid line in the figure) and the command value of the impact frequency (dotted line in the figure). In this case, as shown in FIG. On the other hand, as shown in the flow chart of FIG. 7, for example, when the same kind of screw 4 is continuously screwed in, the previous time recorded in the RAM unit 19 of the memory unit 8 with time is used. If the drive unit 1 is controlled based on the natural frequency at the time of screw tightening, the gap G can be reduced. As described above, by using the past natural frequency at the time of screw tightening and loosening recorded in the memory unit 8 to calculate the predicted value p of the natural frequency at the time of current screw tightening and loosening, the gap G is reduced and the large rotational speed is increased. A torque can be obtained.

Then, as shown in the flowchart of FIG. 8, the natural frequency at the time of the previous screw tightening and loosening recorded in the RAM unit 19 of the memory unit 8 with time is further converted to the natural frequency detected at the current screw tightening and loosening. Correction using PID control based on the natural frequency at the next impact predicted from the frequency, and using the predicted value p of the natural frequency in the current screw tightening work, also corrects subtle deviations in the natural frequency. As a result, the rotational torque can always be kept strong.

In addition, as shown in FIG. 9, a touch panel 26 serving as parameter input means D is connected to the arithmetic processing unit 15, and the thickness, length, type, and the like are stored in a database in the ROM unit 20 of the memory unit 8 by the touch panel 26. The parameters that characterize the screw 4 such as the material are recorded together with the natural frequency when the screw 4 is used, and when the operator inputs the parameters, the predicted value of the natural frequency is used by using the record of the corresponding natural frequency. It is also possible to calculate p.

It should be noted that the natural vibration of the torsional vibration system 3a is not limited to the case where the torsional vibration system 3 is the torsional vibration system 3b including the screw 4 as described above. Providing the same natural frequency detecting means A for detecting the number, the same impact frequency changing means B, and the same automatic torque amplifying means C, it is possible to use the bit 35 of various forms suitable for the work. The user can always perform the tightening and tightening work with a large rotating torque without having to make adjustments by himself.

The case where the hammer 21 strikes the anvil 31 at the natural frequency of the torsional vibration systems 3a and 3b has been described above. However, the present invention is not limited to this. The natural frequency of the torsional vibration system 3a, 3b is a multiple (2, 3, 4,...) Times the natural frequency of the natural frequency of the torsional vibration system 3a, 3b. / 4,...), It is possible to effectively amplify the rotational torque caused by the impact of the hammer 21 by utilizing the resonance phenomenon in the torsional vibration systems 3a and 3b.

For example, in FIG. 10A, when the natural frequency of the torsional vibration system 3a including the anvil 31 and the bit 35 is 196 Hz, the torsion vibration system 3a is fixed to the bit 35 while changing the impact frequency of the hammer 21 to the anvil 31. FIG. 10 (b) shows a graph in the case where the natural frequency of the torsional vibration system 3a is 67 Hz. FIG. 5 shows a graph when the rotational torque is measured while measuring. Although the natural frequencies are different between FIG. 10A and FIG. 10B, the two graphs show that the rotational torque has the highest value under the condition that the impact frequency matches the natural frequency of the torsional vibration system 3a. At the same time, the condition that the impact frequency is twice the natural frequency of the torsional vibration system 3a, or the impact frequency is 1/2, 1/3, 1/4, 1 / It can be observed that the peak value of the rotational torque appears even under the condition of 5 times. Since the same peak value is also observed in the torsional vibration system 3b including the screw 4, for example, when the operation efficiency is prioritized in performing the screw tightening operation, the peak value is maintained until the screw 4 is seated. Driving is performed at a striking frequency that matches an integer (2, 3, 4,...) Times 2 or more of the natural frequency, and after sitting, driving is performed at a striking frequency that matches the natural frequency. In particular, when quietness is required, a hit that matches the reciprocal (1/2, 1/3, 1/4,...) Times an integer of 2 or more of the natural frequency before the screw 4 is seated. It is sufficient to drive at a frequency and drive at a striking frequency that matches the natural frequency only when sufficient rotational torque is required after seating.

Although the impact tool of the above-described example has been described as performing the work of tightening and loosening screws and nuts (mainly as performing the work of tightening screws), the same applies to the impact tool performing other work such as drilling work. Of course, it is possible to provide a compact, lightweight, low-noise, and powerful rotary torque generator.

Next, another example of the impact tool according to the embodiment of the present invention will be described. The impact tool of the other example is not of a direct impact structure in which a large impact torque is generated by a direct impact as in the impact tool of the example. The only difference is that the anvil 31 is of a non-contact striking structure in which a non-contact magnetic striking is applied to the anvil 31 and a strong rotational torque is generated by this striking impact. Only the non-contact hitting structure will be described.

As shown in FIGS. 11A to 11C, the non-contact striking structure includes a driving unit 1 including a motor 11 and a speed reducer 12, and a projection protruding from the driving unit 1 and rotated by the driving unit 1. A drive shaft 13 to be driven, a hammer 21 that rotates together with the drive shaft 13 while being connected thereto, an anvil 31 rotatably provided on the outer peripheral side of the hammer 21, and a shaft 31 a of the anvil 31 connected to the shaft 31 a. And a bit (not shown) that performs a rotational movement together with the hammer 21 and the anvil 31 facing each other via a predetermined gap 40 in the radial direction. It is sufficient to dispose the magnetic pole portion 41 in the opposing portion and dispose the magnetic body 42 in the opposing portion on the anvil 31 side. As a result, when the hammer 21 rotates with respect to the anvil 31, a non-contact impact is applied to the anvil 31 by magnetic attraction torque generated between the magnetic pole portion 41 and the magnetic body 42. Strong rotational torque is generated by the impact.

(4) More specific structures of the hammer 21 and the anvil 31 are as follows. That is, the hammer 21 has a substantially cylindrical hammer core 44 that is press-fitted and fixed to the distal end of the drive shaft 13, and mounting portions 45 protruding from equally-spaced locations on the outer peripheral surface of the hammer core 44. A magnet 46 attached to the tip of each mounting portion 45, and magnetic pole plates 47, 47 for sandwiching and attaching the mounting portion 45 and the magnet 46 at each location from opposite sides in the circumferential direction. The magnetic pole portion 41 is constituted by the magnetic pole plates 47 and 47 sandwiching the magnetic pole portion. The anvil 31 is composed of a shaft portion 31a having a bit hole 46 into which a bit can be freely inserted and removed, and an L-shaped magnetic body 42 protruding from a portion of the outer peripheral surface of the shaft portion 31a at equal intervals in the circumferential direction. A hammer 21 is press-fitted and fixed to the drive shaft 13, and the distal end of the drive shaft 13 is inserted into a bearing 49 disposed on the rear end surface of the shaft portion 31 a of the anvil 31. When the shaft 31a of the anvil 31 is inserted into the bearing 51 disposed on the inner surface of the distal end portion, and the drive shaft 13, the hammer 21 and the anvil 31 are assembled and connected in the case 50, the magnetic pole 41 on the hammer 21 side An anvil arm 48 (that is, the magnetic body 42) on the side of the anvil 31 is opposed to the anvil arm one by one in a radial direction via a minute predetermined gap 40 to generate magnetic attraction.

The structure of the hammer 21 and the anvil 31 is not limited to this, but may be a structure in which the anvil 31 is rotatably positioned on the inner peripheral side of the hammer 21. Further, the arrangement of the magnetic pole portion 41 and the magnetic body 42 is not limited to this, and the magnetic pole portion 41 is provided on one of the opposing portions of the hammer 21 and the anvil 31 and the magnetic body 42 is provided on the other. Anything is fine.

Then, using a non-contact impact structure impact tool shown in FIGS. 11A to 11C, for example, a bit for screwing is inserted into the bit hole 36 of the shaft portion 31a of the anvil 31, and a screw ( When the motor 11 is driven while being engaged and pressed (not shown), the hammer 21 is rotationally driven via the speed reducer 12 and the drive shaft 13, and the screw is tightened as follows. That is, in the initial stage of the screw tightening, the magnetic attraction torque generated by the magnetic attraction force between the magnetic pole portion 41 of the hammer 21 and the magnetic body 42 of the anvil 31 is larger than the rotation torque required for screw tightening. And the anvil 31 are integrally rotated and driven, and the screw tightening operation is continuously performed. When the required rotation torque exceeds the magnetic attraction torque generated between the magnetic pole portion 41 and the magnetic body 42, the hammer 21 performs a rotating motion with respect to the anvil 31, and the rotating motion of the hammer 21 Accordingly, a non-contact impact is applied to the anvil 31 and a large rotating torque is generated. This so-called magnetic impact state allows the screw to be securely tightened, so that the screw can be securely tightened while having much higher quietness than an impact tool having a direct impact structure.

It is an explanatory view showing an internal structure of an example of an impact tool in an embodiment of the invention. It is explanatory drawing which shows the rotation angle change of an anvil which arises at the time of the same screw tightening. It is explanatory drawing which shows the rotation torque change of an anvil which arises at the time of the same screw tightening. (A) is an explanatory view showing a natural frequency change of the torsional vibration system generated at the time of screw tightening of the above, and (b) is an explanatory view showing a prediction method of the natural frequency at the time of screw tightening of the same. It is explanatory drawing which shows the relationship between the natural frequency observed at the time of the same screw tightening, and the hitting frequency commanded. It is explanatory drawing which shows the gap of the rotational torque which the same natural frequency gap produces. It is a flowchart which shows the arithmetic processing using the data at the time of the same previous screw tightening. 6 is a flowchart showing a calculation process for performing further correction by a measured value using data at the time of previous screw tightening of the above. It is explanatory drawing which shows the control part at the time of using the database which recorded the natural frequency of various screws. It is a graph which shows the relationship between an impact frequency and rotational torque same as the above, (a) shows the case where the natural frequency is 196 Hz, and (b) shows the case where the natural frequency is 67 Hz. 5A and 5B show another example of an impact tool according to an embodiment of the present invention, in which FIG. 5A is a perspective view of a driving unit, a hammer, and an anvil, FIG. 5B is an explanatory diagram of an internal structure, and FIG. -It is an X-ray sectional view. It is explanatory drawing which shows the internal structure of the conventional impact tool.

Explanation of reference numerals

REFERENCE SIGNS LIST 1 drive unit 3, 3a, 3b torsional vibration system 4 screw 5a rotation angle sensor 5b rotation speed sensor 5c rotation acceleration sensor 5d rotation torque sensor 7 calculation unit 8 memory unit 9 urging means 10 cam mechanism 11 motor 12 reduction gear 13 drive shaft Reference Signs List 17 drive circuit 21 hammer 23 predicted value calculation unit 31 anvil 35 bit 40 predetermined gap 41 magnetic pole part 42 magnetic body A natural frequency detection means B impact frequency change means C automatic torque amplification means D parameter input means

Claims (15)

A drive unit, a drive shaft that is rotationally driven by the drive unit, a hammer that is slidably fitted to the drive shaft via a cam mechanism and that performs a rotational motion together, and an anvil that performs a rotational motion by engagement with the hammer. An impact tool for urging the hammer toward the anvil side and a bit connected to the anvil, wherein the cam mechanism repeatedly engages the hammer and the anvil as a strike, Matching the impact frequency with the natural frequency of the torsional vibration system including the anvil and the bit, or an integer multiple of 2 or more of the natural frequency, or a reciprocal multiple of an integer of 2 or more of the natural frequency. Features impact tool. A drive unit, a drive shaft that is rotationally driven by the drive unit, a hammer that rotates together with the drive shaft while being connected to the drive shaft, an anvil that is rotatably provided on the inner or outer circumference side of the hammer, and an anvil. A bit that rotates together in a connected state, and a magnetic pole portion is disposed on one of opposing portions of the hammer and anvil facing each other via a predetermined gap, and a magnetic body is disposed on the other. Then, in an impact tool that hits the anvil in a non-contact manner with the rotation of the hammer due to the magnetic attraction generated between the magnetic pole portion and the magnetic body, the impact frequency of the hammer to the anvil is determined by: The natural frequency of a torsional vibration system including an anvil and a bit, or an integer multiple of two or more of the natural frequency, or an inverse multiple of an integer of two or more of the natural frequency, is matched. Theft tool. 3. The impact tool according to claim 1, wherein the torsional vibration system includes a screw connected to a bit. Natural frequency detecting means for detecting the natural frequency of the torsional vibration system, impact frequency changing means for changing the impact frequency of the hammer on the anvil, and the natural frequency or natural frequency obtained by the natural frequency detecting means. A torque automatic amplifying means for automatically controlling the striking frequency changing means so that the striking frequency coincides with an integral multiple of two or more or a reciprocal multiple of an integer of two or more of the natural frequency. Item 4. The impact tool according to any one of Items 1 to 3. As a natural frequency detecting means of the torsional vibration system, a rotation angle sensor for detecting a rotation angle of the anvil or the bit, and an arithmetic unit for calculating a natural frequency from a vibration component between impacts of the rotation angle obtained from the rotation angle sensor. The impact tool according to claim 4, wherein the impact tool is provided. As a natural frequency detecting means of the torsional vibration system, a rotation speed sensor for detecting the rotation speed of the anvil or the bit, a rotation angle obtained by integrating the rotation speed obtained from the rotation speed sensor, and a vibration between impacts of the rotation angle The impact tool according to claim 4, further comprising: a calculation unit that calculates a natural frequency from the component. As a natural frequency detecting means of the torsional vibration system, a rotational acceleration sensor for detecting the rotational acceleration of the anvil or the bit, and a rotational angle obtained by double integrating the rotational acceleration obtained from the rotational acceleration sensor, and a rotational angle between the impact of the rotational angle. The impact tool according to claim 4, further comprising: a calculation unit that calculates a natural frequency from the vibration component. As a natural frequency detecting means of the torsional vibration system, a rotating torque sensor that detects the rotating torque of the anvil or the bit, and an arithmetic unit that calculates a natural frequency from a vibration component between the impacts of the rotating torque obtained from the rotating torque sensor. The impact tool according to claim 4, wherein the impact tool is provided. 9. An initial natural frequency detection mode in which the anvil is rotated only for a short time during which no impact occurs and an initial value of the natural frequency of the torsional vibration system is detected by the natural frequency detecting means. Impact tool according to any of the above. A memory unit that records the natural frequency obtained by the natural frequency detection unit over time in the automatic torque amplification unit, and a predicted value calculation that calculates a predicted value of the natural frequency based on the natural frequency recorded in the memory unit The impact tool according to any one of claims 4 to 9, further comprising a part. In the predicted value calculation unit, the past natural frequency at the time of screw tightening and loosening recorded in the memory unit is used to calculate the predicted value of the natural frequency at another screw tightening and loosening after the screw tightening and loosening. The impact tool according to claim 10, characterized in that: In the predicted value calculation unit, the natural frequency in the past screw tightening and loosening recorded in the memory unit is corrected by the natural frequency detected during the current screw tightening and loosening, and the natural vibration in the current screw tightening and loosening work is corrected. The impact tool according to claim 11, wherein the number is a predicted value. Each parameter characterizing the used screw is recorded in the memory together with the natural frequency, and the next time the screw is tightened, the predicted value of the natural frequency is calculated using the recording of the corresponding natural frequency by inputting each parameter. The impact tool according to any one of claims 10 to 12, further comprising a parameter input unit for performing the operation. The impact tool according to any one of claims 1 to 13, wherein the driving unit is formed by a motor and a speed reducer, and a driving circuit that changes the number of revolutions of the motor is provided as a striking frequency changing unit. The drive unit is formed by a motor and a continuously variable speed reducer, and a drive circuit that changes a reduction ratio of the speed reducer is provided as a striking frequency changing unit. Impact tool.

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