JP2750585B2 - Impact wrench - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impact wrench for rotating a rotating shaft using compressed air or electricity to intermittently apply an impact force to a bolt, a nut, or the like, and tighten the impact wrench.

[Conventional technology]

The impact wrench is a static wrench that tightens the bolts and nuts by applying a continuous tightening force manually or electrically and tightens with intermittent impact force, so it is not possible to read the tightening torque by installing a torque meter . For this reason, a method has been proposed in which a torque detector using a strain gauge is attached to the tip of an impact wrench to detect a tightening torque.
No. 63-190).

As is well known, a torque detector using this strain gauge has four strain gauges attached to the surface of a shaft to be measured to form a bridge circuit, and the resistance of the strain gauge due to the torsion of the shaft due to torque. The change is detected to determine the torque.

[Problems to be solved by the invention]

However, a torque detector using a strain gauge uses a slip ring or an AC transformer in an electric circuit for detecting a change in resistance of the strain gauge, and each of these slip rings or the AC transformer has noise. It is easy to generate, especially for the detection of impact torque.
N) cannot be obtained sufficiently. For this reason, when the tightening torque is detected using a torque detector and when the driving of the impact wrench is automatically stopped when the tightening torque reaches a preset torque, the detected torque and the actual tightening torque match. However, there was a drawback that the actual tightening torque had a large variation and could not be put to practical use. Therefore, detection of torque by a magnetostrictive sensor that does not use a slip ring or an AC transformer can be considered.

In general, a magnetostrictive sensor has two coils arranged close to and perpendicular to a rotation axis so that a magnetic flux generated by exciting one of the coils is transmitted through the rotation axis, and the other is based on the distortion of the axis. This is to detect a magnetic flux deformed due to a change in the generated magnetization direction. Therefore, since the magnetostrictive torque sensor can detect the torque by disposing the coil in non-contact with the rotating shaft, by mounting the magnetostrictive sensor on the impact wrench, it is possible to easily extract a torque detection signal with less noise. Can be.

However, in the magnetostrictive torque sensor, even when there is no load, the detection signal in the circumferential direction of the shaft fluctuates greatly with the rotation of the rotating shaft as shown in FIG. This ninth
The data shown in the figure is obtained when the sensitivity is adjusted so that the output voltage becomes 820 mV when the torque is 5 kg-m, and the detection signal in the circumferential direction when there is no load fluctuates by 1000 mV or more. Since the output fluctuation at the time of no load acts as the fluctuation of the zero point, there is a disadvantage that the detected torque becomes a value different from the actual torque. Therefore, various methods have been disclosed to solve this problem.

For example, a method of forming a coating of a magnetic material on the surface of a rotating shaft to improve the magnetic characteristics of the rotating shaft (Japanese Patent Publication No. 52-14 / 1982)
No. 985), a method in which an amorphous magnetic ribbon having remarkable magnetostriction characteristics is wound around a rotating shaft and fixed, and the strain stress of the rotating shaft is detected through the magnetic strain of the amorphous magnetic ribbon (Japanese Patent Application Laid-Open No. 58-9904). Japanese Patent Application Laid-Open No. Sho 62-15427) discloses a method in which sampling is always performed at a fixed position on the rotating shaft to eliminate the influence of variations in magnetization in the circumferential direction of the rotating shaft (Japanese Patent Application Laid-Open No. 62-15427). The detected value in the circumferential direction is stored as an offset component,
A method of obtaining a torque by subtracting an offset component from a detection signal when a load is acting on a rotating shaft (Japanese Patent Laid-Open No. Sho 62-55)
No. 533).

However, when forming a coating made of a magnetic material on the surface of the rotating shaft, it is difficult to make the thickness of the coating uniform. In addition, when the amorphous magnetic ribbon is wound around the surface of the rotating shaft, the amorphous magnetic ribbon is distorted, and it is difficult to bring the amorphous magnetic ribbon into close contact with the rotating shaft. The method of sampling at a fixed position on the rotating shaft and the method of storing the detected value in the rotating shaft circumferential direction when there is no load require a means for detecting the rotation angle, and the sensor becomes large and expensive. Has disadvantages.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned drawbacks of the related art, and has as its object to provide an impact wrench excellent in the accuracy of detecting a tightening torque.

[Means for solving the problem]

The present invention focuses on the fact that the fluctuation of the zero point in the circumferential direction of the rotating shaft is based on the fact that the quenching process is performed to obtain the strength of the rotating shaft, and the quenching process makes the residual stress distribution of the rotating shaft random. In order to achieve the above object, the rotating shaft is rotated by a driving device,
In an impact wrench for intermittently applying a tightening force to a bolt or a nut or the like, a magnetostrictive sensor is provided in proximity to the rotating shaft, and the rotating shaft has a magnetostrictive sensor-facing portion from which residual stress is removed over the entire circumference, A portion other than the magnetostrictive sensor facing portion is surface-hardened.

[Action]

The rotating shaft in the impact wrench is formed of steel and quenched to obtain strength enough to withstand the tightening torque. Then, the quenched steel is structurally unstable when quenched, and if left as it is, the internal stress increases and cracks occur. Therefore, tempering is performed after quenching. However, tempering is generally aimed at improving toughness, and internal stress remains in the tempered shaft, and this residual internal stress causes magnetization variation in the circumferential direction of the shaft, causing zero point fluctuation. Become. Therefore, if the internal stress remaining on the shaft is removed, the variation in the magnetization in the circumferential direction of the shaft can be reduced, and the fluctuation of the detection signal (zero point) in the circumferential direction when no load is applied is reduced.
When the detected tightening torque matches the actual tightening torque, the accuracy of detecting the tightening torque is improved, and when the detected tightening torque reaches the set value,
The driving of the impact wrench can be automatically stopped.

〔Example〕

A preferred embodiment of the impact wrench according to the present invention,
This will be described in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a main part of an impact wrench according to an embodiment of the present invention.

In FIG. 1, an impact wrench 10 has a rotating shaft 12 formed of, for example, carbon steel, and a tip of the rotating shaft 12 protrudes from an outer cylinder 14 so that the tip rotates a bolt or a nut. A connecting portion 16 for connecting a socket (not shown). The rear end of the rotating shaft 12 is connected to a connecting portion 18 of a well-known air drive unit (not shown) operated by compressed air. A pair of magnet pieces 20 are attached to the intermediate portion of the rotating shaft 12 so as to be shifted in the axial direction and at an angle of 90 °. And, in the outer cylinder 14,
A rotation angle sensor 22 provided with the tip close to the magnet 20 is fixed. The rotation angle sensor 22 is a sine sensor arranged at 90-degree intervals around the rotation shaft 12 as shown in FIG.
22a and a pair of cosine sensors 22b.

In the outer cylinder 14, further on the tip side than the rotation angle sensor 22,
A magnetostrictive sensor 24, which will be described in detail later, is provided in the vicinity of the rotating shaft 12. Then, the rotating shaft 12 is subjected to an annealing process at the detecting unit 26 facing the magnetostrictive sensor 24, the residual stress is removed over the entire circumference, the magnetization characteristics in the circumferential direction are made uniform, and the detecting unit 26 is rotated. Parts other than 26 are surface hardened by induction hardening, flame hardening, nitriding, etc.
Improvements in wear resistance and strength are achieved.

The annealing treatment differs depending on the type of steel.
Is heated to 500 to 600 ° C., maintained at this temperature for a required time, and then gradually cooled to room temperature. By this annealing process, most of the residual stress can be removed, the variation in the magnetization characteristics of the rotating shaft 12 in the circumferential direction can be greatly improved, and the detection signal of the circumferential direction when the rotating shaft 12 is not loaded can be obtained. Fluctuations can be made very small compared to conventional rotating shafts without annealing.

FIG. 5 is a characteristic diagram showing the zero point movement indicating the annealing effect of the rotating shaft 12.

FIG. 5 plots the output voltage between 5 kg-m and no load when the load applied to the rotating shaft 12 is changed and the hysteresis of the output voltage at 60 ° intervals in the circumferential direction of the rotating shaft 12 is obtained. The maximum value of the zero shift is
It is about + 6% of the rated output (5000mV), and the zero point movement can be greatly improved compared to the conventional one. As a result, the detection error of the magnetostrictive sensor 24 can be significantly reduced as compared with the related art, and the tightening torque can be accurately detected. When the tightening torque reaches a preset torque, the driving of the impact wrench 10 is performed. Can be automatically stopped.

The magnetostrictive sensor 24 is, as shown in FIG.
28 and a detection coil 30. The excitation coil 28
It is wound around a U-shaped excitation core 32 arranged orthogonally to the axial direction of the rotating shaft 12. The detection coil 30 is
It is wound inside a U-shaped detection core 34 which is located inside the axis 32 and is parallel to the axis of the rotating shaft 12.

The excitation coil 28 is connected to the excitation circuit 36,
And generates a magnetic flux that passes through the rotating shaft 12 in response to an exciting current. On the other hand, the detection coil 30 detects a magnetic flux transmitted through the rotating shaft 12, and inputs a voltage corresponding to the detected magnetic flux to the detection circuit 38 as a detection signal. The detection circuit 38 also receives detection signals from the sine sensor 22a and the cosine sensor 22b. The output signal of the detection circuit 38 is input to a torque calculation circuit 40 for calculating torque, and the torque value obtained by the torque calculation circuit 40 is sent to the display 42 and the comparison circuit 44. You.

As shown in FIG. 4, the excitation circuit 36 has an excitation amplifier 46 whose frequency is adjusted by a frequency adjuster 48 and whose amplitude is adjusted by an amplitude adjuster 50, and which excites an excitation current having a predetermined frequency and a predetermined amplitude. Supply to coil 28.

The detection circuit 38 is an AC circuit that amplifies the detection signal of the detection coil 30.
The controller includes controllers 54 and 56 for processing output signals of the amplifier 52, the sine sensor 22a, and the cosine sensor 22b. Then, the detection signal of the detection coil 30 amplified by the AC amplifier 52 is
After being detected by the detector 58, it is amplified by the DC amplifier 60. A coarse adjustment knob 62 and an auto zero adjuster 64 are connected to the DC amplifier 60, and the zero point of the torque value displayed on the display 42 is adjusted.

On the other hand, the outputs of the controllers 54 and 56 are connected to buffer amplifiers 66 and 68, respectively.
In response to the angular position signals detected by the sine sensor 22a and the cosine sensor 22b via the controller 68, the controllers 54 and 56
The cosine waveform oscillates and is displayed on the display units 70 and 72.

The torque calculation circuit 40 includes a DC amplifier 60 and a buffer amplifier 6
Analog-to-digital converters (A / D converters) 74, 7 that convert analog signals output by 6, 68 into digital signals
6, 78, a rotation angle calculator 80 that receives the outputs of the A / D converters 76, 78 and calculates the rotation angle of the rotation shaft 12, and a memory 82 that stores zero point correction data and sensitivity correction data. An A / D converter 74 and a torque calculator 84 for obtaining a torque acting on the rotary shaft 12 based on the output of the rotation angle calculator 80 are provided.

The zero point correction data stored in the memory 82 is
Is the circumferential detection value detected by the magnetostrictive sensor 24 at the time of no load, and corresponds to the rotation angle of the rotating shaft 12. The sensitivity correction data is a coefficient such that the difference between the no-load detection data and a predetermined torque, for example, a detection value when 5 kg-m is applied, becomes a predetermined value (for example, +5000 mV or -5000 mV). This also corresponds to the rotation angle.

The torque obtained by the torque calculator 84 is stored in a buffer amplifier 86
Via the display 42, the torque output terminal 88 and the comparison circuit 44
To enter. The comparison circuit 44 includes a comparator 90 and a limit setting device 92 for inputting a reference value to the comparator 90. The output side of the comparator 90 is connected to a control output terminal 96 via a relay 94.

The power supply section 98 of each of these circuits is provided with a power switch 10
0, connected to 100 V AC via a fuse 102 and a noise filter 104.

The operation of the embodiment configured as described above is as follows.

In the memory 82, the above-mentioned zero point correction data and sensitivity correction data are stored in advance corresponding to the rotation angle (rotation position) of the rotation shaft 12, for example, for each rotation angle of 1 degree.

A socket (not shown) attached to a connecting portion 16 formed at the tip of the rotating shaft 12 is fitted with a bolt or a nut, and an air driving unit (not shown) is operated to rotate the rotating shaft 12. The exciting coil 28 of the magnetostrictive sensor 24 is an exciting amplifier.
An exciting current having a predetermined frequency and a predetermined amplitude is supplied from 50 to generate a magnetic flux. The magnetic flux generated by the exciting coil 28 exits from one leg of the exciting core 32, passes through the rotating shaft 12, and reaches the other leg. When the rotating shaft 12 is rotated to apply a tightening torque to the bolt or the nut, the rotating shaft 12 is twisted to generate distortion, and the direction of magnetization changes. As a result, a part of the magnetic flux transmitted through the rotating shaft 12 interlinks with the detection coil 30, and the detection coil 30
, A voltage is induced.

The voltage induced in the detection coil 30 is input to the AC amplifier 52 as a detection signal, amplified, and then converted by the detector 58 into a DC detection signal. After the detection signal output from the detector 58 is amplified by the DC amplifier 60, the A / D converter 74
Is converted from an analog value to a digital value, and is sent to the torque calculator 84.

On the other hand, when the rotating shaft 12 rotates, the sine sensor 22a and the cosine sensor 22b detect a periodic change of the magnetic flux generated from the magnet piece 20 attached to the opposed shaft, and input the detected change to the controllers 54 and 56. The controllers 54 and 56 process the detection signals of the sine sensor 22a and the cosine sensor 22b so that the signals have a 360-degree cycle, and the buffer amplifiers 66 and 68
Are displayed on the display units 70 and 72 via the, and are sent to the A / D converters 76 and 78 of the torque calculation circuit 40. A / D converters 76 and 78
The input analog value is converted into a digital value and input to the rotation angle calculator 80. The rotation angle calculator 80 is an A / D converter 7
Sine sensor 22a and cosine sensor 22b output by 6, 78
The rotation angle of the rotary shaft 12 is calculated based on the detected data of the rotation angle, and the rotation angle data is sent to the torque calculator 84, for example, every one degree of the rotation angle.

When the detection signal of the magnetostriction sensor 24 is input from the A / D converter, the torque calculator 84 reads the read signal to the memory 82 based on the rotation angle of the rotating shaft 12 obtained by the rotation angle calculator 80 at this time. To read out the zero point correction data and sensitivity correction data at the rotation angle. Then, the torque calculator 84 subtracts the value of the zero-point correction data from the value detected by the detection coil 30, multiplies the subtracted value by the sensitivity correction data, corrects the detection value, and corrects the detected value. And calculates and outputs the torque.

The value of the torque output by the torque calculator 84 is displayed on the display 42 via the buffer amplifier 86, and is also output to the comparator 90 and the torque output terminal 88 of the comparison circuit 44. The reference value is input to the comparator 90 by the limit setting device 92. When the torque value output from the torque calculator 84 reaches the reference value, for example, “1” is output and the relay 94 is output.
Activate When the relay 94 is activated, the control output terminal 96
Thus, a signal for closing the electromagnetic valve interposed between the impact wrench 10 and a compressed air source (not shown) is output, the electromagnetic valve is closed, and the operation of the air drive unit of the impact wrench 10 is stopped. The torque value input to the torque output terminal 88 is sent to an external device such as a printer.

FIG. 6 shows time-series data of torque output when the nut is tightened according to the embodiment. The nut was tightened with an air pressure of 4 kg / cm ² , and the maximum instantaneous value of the detected torque indicated on the display 42 was 6.78 kg-m. At this time, the torque detected by the torque measuring device when the nut was loosened by the spanner was 6.2 kg-m, and the torque detected by the example was about 10% larger.

As described above, in the embodiment, the error of the detected torque can be significantly reduced as compared with the related art.
It has become possible to automatically stop the drive of ten.

In the above embodiment, the exciting coil 28 is
Although the case where it is arranged perpendicular to the 12 axes has been described, the excitation coil 28 is arranged along the axis and the detection coil 30
May be orthogonal to the axis. Further, the exciting coil 28 and the detecting coil 30 may be wound around the rotating shaft 12 in an overlapping manner.
Further, in the above-described embodiment, the case where the zero point correction and the sensitivity correction are performed by the torque calculator 84 has been described. However, these corrections can be omitted. Further, in the above-described embodiment, the case where the residual stress is removed by the quenching process is described. However, the present invention is not limited to this, and the residual stress may be removed by another method such as a mechanical method.

 FIG. 7 shows another embodiment of the rotating shaft.

The rotating shaft 12 shown in FIG. 7 has a larger diameter than the other parts of the detecting portion 26 which has been subjected to the annealing process. This makes it possible to reinforce the strength of the detection unit 26 that has been reduced by the annealing process.

FIG. 8 shows a sectional view of still another embodiment of the rotating shaft.

The rotating shaft 12 shown in FIG. 8 is driven by the rotating shaft 12 or the top 11 (the outer periphery of the detecting portion of the rotating shaft) according to the circumferential residual stress or the variation of the magnetization characteristics, that is, the circumferential variation of the detected value when no load is applied. Is mounted so that the detection value at the time of no load can be corrected so as to be uniform in the circumferential direction. However, in this case, it is necessary to provide a sensor for detecting the gap d, such as the optical sensor 106, and obtain the gap d for each rotation angle between the magnetostrictive sensor 24 and the rotating shaft 12 or the top 11, and correct the detection value.

〔The invention's effect〕

As described above, according to the present invention, the magnetostrictive sensor is provided close to the rotating shaft, and the portion of the rotating shaft facing the magnetostrictive sensor is free of residual stress over the entire circumference, so that the tightening torque can be reduced. Can be detected well.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a main part of an impact wrench according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line II-II of FIG. 1, and FIG. 3 is a schematic diagram of a torque detecting circuit of the embodiment. FIG. 4 is a detailed block diagram of the torque detection circuit, FIG. 5 is a characteristic diagram showing an improved state of the variation in the circumferential direction of the rotating shaft by the annealing process, and FIG. Characteristic diagram showing time series data of torque output when tightening,
FIG. 7 is an explanatory view showing another embodiment of the rotating shaft, FIG. 8 is a sectional view of still another embodiment of the rotating shaft, and FIG. 9 is a circumferential direction of a detected value of the conventional rotating shaft when there is no load. FIG. 10… impact wrench, 12… rotary axis, 20… magnet,
22: Rotation angle sensor, 24: Magnetostrictive sensor, 26: Detection unit, 28: Excitation coil, 30: Detection coil.

Continuation of front page (56) References JP-A-63-117230 (JP, A) JP-A-52-122997 (JP, A)

Claims (1)

(57) [Claims] 1. An impact wrench for rotating a rotating shaft by a driving device to intermittently apply a tightening force to a bolt or a nut or the like to provide a magnetostrictive sensor in proximity to the rotating shaft. An impact wrench, wherein a residual stress is removed over the entire circumference of the magnetostrictive sensor facing portion, and a portion other than the magnetostrictive sensor facing portion is subjected to a surface hardening treatment.