Impact tightening tool

[Technical Field to which the Invention belongs] The present invention relates to an improvement of a striking tightening tool such as an impact wrench or an impact driver.

[Conventional Technique] An impact wrench, an impact driver, or the like is often used as a striking tightening tool for firmly tightening screws such as bolts and nuts. This type of tool includes, for example, a hammer that is rotated by a drive source such as an electric motor or an air motor, and an anvil that engages with screws to rotate the screws. The hammer and the anvil collide with each other, and the hammer rotates the anvil. Then, when a force exceeding a predetermined value acts between the hammer and the anvil, the hammer is linked so as to idle with respect to the anvil. In order to provide such a configuration, the hammer continuously rotates the anvil and continuously tightens the screws while the screws are screwed with a light load. Then, when the screws are tightened and a force equal to or higher than a predetermined value acts between the anvil and the hammer, the hammer starts to idle, and after idling at a predetermined angle, collides with the anvil. By repeating the operation of idling and collision, the anvil rotates each time the hammer collides, and the screws are tightened each time.

[0003] In the impact tightening tool described above, the final screw tightening torque depends on the number of collisions between the hammer and the anvil. For this reason, a technique for adjusting the tightening torque based on the number of collisions between the hammer and the anvil has been conventionally developed (for example, Japanese Patent Application Laid-Open No. 5-200677). In the technique described in the above publication, the collision between the hammer and the anvil is detected by the microphone that receives the collision sound between the hammer and the anvil. Then, when the hammer and the anvil collide with each other a preset number of times, the movement of the drive source that rotates the hammer is stopped. As a result, the hammer and the anvil collide with each other a preset number of times, and the screws are tightened with an appropriate tightening torque.

[0004] However, in the striking tightening tool described above, since the microphone is used as the sound receiving member for detecting the collision sound, the detection signal output from the microphone is relatively wide. Sound in the frequency domain is converted into an electrical signal. Therefore, the electric signal output from the microphone is an electric signal that includes not only a collision sound but also many noise components such as a reverberant sound reverberated by a material to be fastened such as a steel frame and a sound generated from a drive source. Therefore, depending on the working environment and the like, it may be difficult to detect (determine) the collision between the hammer and the anvil from these electric signals.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to detect a collision between a hammer and an anvil by reducing a noise component contained in an electric signal output from a detecting means. Realize a striking tightening tool that can be facilitated.

[Means, Actions and Effects for Solving the Problems] The striking tightening tool according to claim 1 for solving the above problems is a striking tightening tool that rotates an anvil when a hammer collides with an anvil. In the above, the detection means for detecting the collision sound between the hammer and the anvil and the drive source for rotating the hammer are controlled based on the number of collision sounds between the hammer and the anvil detected by the detection means.<u style="single">Microcomputer</u>To be equipped. The detection means is arranged away from the hammer, anvil, and rotational drive source, and has a characteristic of converting sound in a specific frequency region into a larger electric signal than sound in another frequency region.<u style="single">Piezoelectric buzzer</u>Consists of the frequency peak of the collision sound within its specific frequency domain<u style="single">In addition, the peak of the output sound pressure of the piezoelectric buzzer substantially coincides with the frequency peak of the collision sound. Then, the piezoelectric buzzer is connected to the input port of the microcomputer without a filter that removes noise.</u>It is characterized by being. In the impact tightening tool, the detection means is located away from the hammer, anvil and rotary drive source. The detection means detects the collision sound generated when the hammer and the anvil collide,<u style="single">Microcomputer</u>Controls the rotational drive source based on the number of collision sounds detected by the detection means. This detection means has a characteristic of converting a sound in a specific frequency region into a larger electric signal as compared with a sound in another frequency region.<u style="single">Piezoelectric buzzer</u>It is composed of, and the frequency peak of the collision sound is included in the specific frequency region.<u style="single">Also, the peak of the output sound pressure of the piezoelectric buzzer almost coincides with the frequency peak of the collision sound.</u>.. Therefore, the collision sound between the hammer and the anvil is converted into a large electric signal.<u style="single">On the other hand</u>, Sounds other than the specific frequency range (noise such as reverberation) are converted into large electrical signals.<u style="single">Instead, noise components other than the collision sound are removed from the electric signal output from the piezoelectric buzzer. Therefore, the piezoelectric buzzer that detects the collision sound can be connected to the input port of the microcomputer without using a filter that removes noise.</u>[0007] In the impact tightening tool according to claim 1,<u style="single">It is preferable that the control means and the detection means are incorporated on the same substrate.</u>[Embodiment of the Invention] Next, a striking tightening tool embodying the present invention will be described with reference to the drawings. FIG. 1 shows a partial cross-sectional side view of the impact wrench 1. Reference numeral 3 in the figure shows a housing in which the motor 22, which is a rotational drive source, is housed and fixed. A gear is formed on the output shaft 20 of the motor 22 (which is pivotally supported by the bearing 19), and a plurality of planetary gears 12 are meshed with this gear. The planetary gear 12 has a pin 14 as an axis, and the pin 14 is fixed to a spindle 8 pivotally supported by a bearing 23. Further, the planetary gear 12 is located on the inner diameter side of the internal gear 16 fixed to the internal gear case 18 and meshes with the internal gear 16. The reduction mechanism is composed of these gear trains. The spindle 8 fixing the pin 14 is rotationally driven by the motor 22. A plurality of grooves 8a are formed in a V shape on the spindle 8, and a hammer 4 can idle on the spindle 8. A ball 6 is interposed between the hammer 4 and the groove 8a. The cam mechanism is composed of the groove 8a and the ball 6, and the hammer 4 can move relative to the spindle 8 along the groove 8a. Further, a spring 10 is housed between the hammer 4 and the spindle 8 in a compressed state via a ball 51 and a washer 49, and the hammer 4 is always urged to the right in the drawing. Anvil 2 is rotatably attached to the housing 3 on the tip side of the hammer 4. The tip 2a of the anvil 2 has a polygonal cross section, to which a box (not shown) that engages with the heads of nuts is attached. A pair of ridges 2b and 2c extending in the radial direction are formed on the rear end surface of the anvil 2. In addition, ridges 4b and 4c extending in the radial direction are also formed on the tip surface of the hammer 4, so that the side surfaces of the ridges 2b and 2c and 4b and 4c come into contact with each other.

Next, the operation of the tightening mechanism described above will be described. When the nuts are tightened with a light load in the above-mentioned tightening mechanism, the force acting between the ridges of the anvil 2 and the hammer 4, that is, the force acting between the spindle 8 and the hammer 4 via the ball 6 is also weak. , The hammer 4 is pressed against the anvil 2 by the force of the spring 10. Therefore, the rotation of the spindle 8 is continuously transmitted to the hammer 4 and the anvil 2, and the nuts (not shown) are continuously tightened. On the other hand, when the tightening force of the nuts becomes large, a large force also acts between the ridges of the anvil 2 and the hammer 4, and a large force also acts between the spindle 8 and the hammer 4 via the ball 6. Will be. Therefore, the force for moving the hammer 4 to the rear side of the spindle 8 along the groove 8a also increases. That is, when a force exceeding a predetermined value acts between the anvil 2 and the hammer 4, the hammer 4 retracts and the contact relationship between the ridges 2b and 2c and the ridges 4b and 4c is lost, and the hammer 4 with respect to the anvil 2. Idle around. When the ridges 4b and 4c exceed the ridges 2b and 2c, the spring 10 advances the hammer 4. Therefore, the hammer 4 collides with the anvil 2 after swinging at a predetermined angle. This phenomenon of idling and collision is repeated, and the nuts are tightened more firmly at each collision.

[0010] Next, various switches provided on the handle portion 3a will be described. The handle portion 3a is provided with a main switch 48 for activating the motor 22 which is a rotation drive source and a forward / reverse changeover switch 24 for switching the rotation direction of the motor 22. Further, at the lower end of the handle portion 3a, a dial setting portion 34 for setting the number of collisions between the hammer 4 and the anvil 2 is provided. The dial setting unit 34 can be operated (change of the set number of times, etc.) with the battery pack 122 removed from the striking tightening tool 1. This is to prevent unintentional setting changes by the user.

[0011] Further, a control board 36 is attached to a position in the handle portion 3a from the lower end, and electronic components such as a microcomputer 38 and a switching element 40 are mounted therein. Further, the control board 36 incorporates a sound receiving unit 30 (piezoelectric buzzer) that receives the collision sound of the hammer 4 and the anvil 2.

Next, the circuit configuration of the impact tightening tool 1 will be described with reference to FIGS. 2 to 4. The microcomputer 38 mounted on the control board 36 is a microcomputer in which the CPU 110, ROM 118, RAM 120 and I / O 108 are integrated into one chip, and is connected as shown in FIG. A control program or the like for controlling the operation of the motor 22 is stored in the ROM 118 of the microcomputer 38. The sound receiving unit 30 is connected to one terminal of the comparator 104 via the filter 102. The voltage V3 of the reference voltage generator 112 is input to the other terminal of the comparator 104. The output voltage of the comparator 104 is input to the microcomputer 38. The battery pack 122, which is a power source, is connected to the motor 22 via a main switch 48, a forward / reverse changeover switch 24, and a switching element 40. The switching element 40 is connected to the microcomputer 38 via the switching circuit 114. The dial setting unit 34 is also connected to the microcomputer 38.

Next, a specific circuit configuration of the sound receiving unit 30, the filter 102, and the comparator 104 in the above-described circuit will be described with reference to FIG. As shown in FIG. 3, the sound receiving unit 30 is connected to the 12V power supply via the resistor R1 and is connected to one terminal of the capacitor C1. The other terminal of the capacitor C1 is connected to one terminal of the comparator 104, and the other terminal of the comparator is connected to the reference voltage generator Vref. Further, the point B between the capacitor C1 and the comparator 104 is connected to the ground wire via the diode D3 and the 5V power supply via the diode D2. On the other hand, a microcomputer 38 is connected to point A between point A and point C1 in the figure, and a buzzer signal for generating sound is input from the sound receiving unit 30 (piezoelectric buzzer). .. Specifically, the point D is connected to the collector terminal of the transistor TR via the diode D1, the base terminal of the transistor TR is connected to the output port of the microcomputer 38 that outputs the buzzer signal, and the emitter terminal of the transistor TR is grounded. It is connected to a wire.

Next, the operation of the circuit described above will be described with reference to FIG. First, the action when the hammer 4 collides with the anvil 2 due to the rotation of the motor 22 and a collision sound is generated will be described. When the hammer 4 and the anvil 2 collide with each other and a collision sound is generated, a voltage V1 is generated from the sound receiving unit 30. As shown in FIG. 4A, this voltage V1 is an AC signal that vibrates up and down with reference to the voltage Vb (voltage obtained by subtracting the voltage drop due to the resistor R1 from the power supply 12V). The DC component of the voltage V1 output from the sound receiving unit 30 is removed by the capacitor C1, and the negative component is removed by the diode D3. The voltage V2 at point B is a signal from which the negative component has been removed, as shown in FIG. 4 (B). The voltage V2 is input to one input terminal of the comparator 104 and is compared with the reference voltage V3 input to the other terminal of the comparator 104. Then, when the output voltage V2 becomes higher than the reference voltage V3, the comparator 104 is turned on, and the output voltage V4 is output from the comparator 104. The output voltage V4 output from the comparator 104 becomes a pulse wave as shown in FIG. 4 (C). This pulse wave is detected at the input port of the microcomputer 38. This pulse wave rises at the time of the collision between the hammer 4 and the anvil 2, and corresponds to the collision sound. Therefore, the microcomputer 38 counts the number of collisions by counting the pulse wave. When the sound receiving unit 30 detects the collision sound, the buzzer signal is not output from the output port of the microcomputer 38, and the transistor TR is turned off.

[0015] On the other hand, when sound is generated from the sound receiving unit 30 (piezoelectric buzzer), a buzzer signal (pulse wave) is output from the output port of the microcomputer 38. This pulse wave turns the transistor TR on and off. Therefore, the voltage at one end of the sound receiving unit 30 (voltage at point A) is also turned on (high)-off (low), and sound is generated from the sound receiving unit 30.

[0016] Here, the sound receiving unit 30 used in the above-described circuit uses a piezoelectric buzzer (PKM22EPP-4001 manufactured by Murata Manufacturing Co., Ltd.). This piezoelectric buzzer outputs sound in a specific frequency region, and the piezoelectric buzzer of the present embodiment has a peak of output sound pressure level near a frequency of 4 kHz. Therefore, when a piezoelectric buzzer is used as a sound receiving member, it has a characteristic of converting a sound in a specific frequency region (frequency around 4 kHz) into a larger electric signal as compared with a sound in another frequency region. The reason for using the piezoelectric buzzer having the peak of the output sound pressure level near 4 kHz as the sound receiving unit 30 of the present embodiment is as follows. That is, the tightening work was actually performed by the striking tightening tool according to the present embodiment, and the collision sound between the hammer 4 and the anvil 2 was measured. The collision sound was measured using a condenser microphone capable of receiving sound in a relatively wide frequency range under experimental conditions in which no reverberant sound was generated. Then, as a result of FFT analysis of this measured sound, a frequency peak (corresponding to the peak of the collision sound) appeared in the vicinity of 4 kHz.

Next, the operation of the striking tightening tool configured as described above will be described. In the striking tightening tool of the present embodiment, the number of striking of the hammer 4 and the anvil 2 is set in the dial setting unit 34, and the rotation of the motor 22 is stopped when the hammer 4 and the anvil 2 collide with each other by the set number of times. Be made to. The processing performed by the microcomputer 38 at this time will be described. This process is executed while the main switch 48 is being operated, the execution is stopped when the main switch 48 is turned off, and the execution is restarted when the main switch 48 is operated again. First, when the main switch 48 is turned on, the number "xy" (10's place is x, 1's place is y) set in the dial setting unit 34 is read and stored in the RAM 120 as a variable xy. Next, it is determined whether or not the value set in the dial setting unit 34 is "00". When "00" is set in the dial setting unit 34, the number of collisions is set to 0, so that the motor 22 does not rotate even if the main switch 48 is operated.

[0018] When it is determined that the set value of the dial setting unit 34 is not "00", it is determined whether or not "99" is set next. Here, "99" is the maximum value that can be set by the dial setting unit 34, and if this maximum value is set, the switching element 40 is turned on. That is, when "99" is set, the motor 22 continues to rotate while the main switch 48 is turned on. By setting "99", the operator can continuously tighten the nuts and the like regardless of the number of collisions between the hammer 4 and the anvil 2.

If neither "00" nor "99" is set, that is, if "01" to "98" are set in the dial setting unit 34, then the forward / reverse changeover switch 24 is used to perform forward rotation. The microcomputer 38 determines whether it is set or the reversal is set. This is determined by discriminating the potential of one of the lead wires between the forward / reverse changeover switch 24 and the switching element 40 as shown in FIG. This potential changes depending on the forward / reverse of the forward / reverse changeover switch 24. When the forward / reverse changeover switch 24 is set to reverse, the motor 22 is rotated while the main switch 48 is turned on. That is, in the case of reverse rotation, the motor 22 is continuously rotated until the main switch 48 is turned off, and the nut or the like is loosened.

When forward rotation is set, the expected number of collisions z is calculated from the number xy set in the dial setting unit 34 and stored in the RAM 120. The expected number of collisions z is calculated by the following formula. z = (x × 10 + y) × 2 + 1 In other words, if 50 (10's place is 5, 1's place is 0) is set in the dial setting unit 34, the number of scheduled collisions is z. Is 101 times. When the scheduled number of collisions is stored in the RAM 120, the switching element 40 is then turned on and the motor 22 is started to rotate. Next, the sound receiving unit 30 detects the collision sound, and waits until the comparator 104 outputs the striking sound detection signal.

[0021] When the pulse wave output from the comparator 104 is detected by the input port of the microcomputer 38, the CPU 110 next performs an operation of subtracting 1 from the scheduled number of hits z stored in the RAM 120. Next, it is determined whether or not the result of subtracting 1 becomes zero, and when it becomes zero, the switching element 40 is turned off and the rotational drive of the motor 22 is stopped. If it is not zero, the above process will be repeated. By these processes, the motor 22 is stopped when the hammer 4 and the anvil 2 collide with each other by the number of times the hammer 4 is scheduled to be hit. As a result, the tightening torque of the nut or the like is managed to a predetermined value.

Next, a signal (output from the sound receiving unit 30) input to the terminal of the comparator 104 when the nuts are tightened using the striking tightening tool (tightening torque 200 Nm class) described above. The experimental result of measuring the signal) will be described. FIGS. 5 and 6 show the experimental results using a piezoelectric buzzer (a striking tightening tool according to the present embodiment) for the sound receiving portion 30, and FIGS. 7 and 8 show a condenser microphone (conventional striking) for the sound receiving portion 30. This is the result of an experiment using a tightening tool). Note that FIGS. 5 and 7 show the results when the measurement was performed so that the reverberant sound was not generated, and FIGS. 6 and 8 show the results when the measurement was performed so that the reverberant sound was generated. In the case of using the piezoelectric buzzer shown in FIGS. 5 and 6, the noise component was removed in both cases of no reverberant sound and with reverberant sound, and a peak (collision sound) could be detected at each striking interval. On the other hand, in the case of using the condenser microphones of FIGS. 7 and 8, in the case of the echo sound shown in FIG. 8, the noise component was too large to detect the impact (collision sound).

As described in detail above, according to the impact tightening tool of the present embodiment, since the piezoelectric buzzer is used for the sound receiving portion 30 for detecting the collision sound, the noise component is removed and the hammer 4 and the anvil are removed. The collision sound of 2 can be detected accurately. In particular, even when a striking tightening tool with a tightening torque of 200 Nm class was used in a state where a reverberant sound was generated, the collision sound could be detected accurately. Further, according to the impact tightening tool of the present embodiment, since it is not necessary to remove the noise component by a high-performance filter or the like, the electric circuit is not complicated and the control board 36 can be manufactured at low cost. .. Further, according to the impact tightening tool of the present embodiment, since the sound receiving unit 30 is a piezoelectric buzzer, the sound receiving unit 30 can be used as a sound source for issuing a warning to the operator. As a result, the sound receiving member for detecting the collision sound and the sound generating member for issuing the warning can be made into the same component, and the mounting space of the control board 36 can be reduced.

[0024] Although one embodiment embodying the present invention has been described above, the present invention is not limited to the above-described embodiment, and can be implemented in each of the following embodiments. However, the embodiments shown below are merely examples, and the present invention should not be construed as being limited to the above-described embodiments or the following embodiments.

(1) In the above-described embodiment, the buzzer is used as a means for detecting the collision sound between the hammer and the anvil, but the detection means for detecting the collision sound is not limited to the buzzer, and for example, the natural frequency is used. A sound receiving member can be configured by a vibrating body that matches the frequency peak of the collision sound and a conversion means that converts the vibration of the vibrating body into an electric signal. Further, for example, the sound receiving member may be composed of a dynamic speaker that generates only a sound having a specific frequency.

(2) In the above-described embodiment, the electrical signal output from the detection means is directly input to the microcomputer without passing through a special filter, but the configuration is not limited to this. , The electric signal output from the detection means may be further removed by a filter or the like. This makes it possible to further easily detect the collision sound.

(3) In the above-described embodiment, a piezoelectric buzzer having a peak at a frequency of 4 kHz is used as the sound receiving member, but the frequency characteristics of the piezoelectric buzzer include the maximum tightening torque of the impact tightening tool and the housing. It is preferable to select an appropriate one depending on the shape and the like. At this time, the frequency characteristic of the piezoelectric buzzer may be determined by actually measuring the collision sound, or the frequency characteristic may be determined by using the result of sound analysis or the like using a computer.

[0028] Although some embodiments of the present invention have been described in detail above, these are merely examples, and the present invention is implemented in various modifications and improvements based on the knowledge of those skilled in the art. be able to.

BRIEF DESCRIPTION OF THE DRAWINGS [FIG. 1] A partial cross-sectional side view of a striking tightening tool according to the present embodiment.

FIG. 2 is a block diagram showing a circuit configuration of a striking tightening tool according to the present embodiment.

FIG. 3 is a diagram showing a specific circuit configuration of a striking tightening tool according to the present embodiment.

FIG. 4 is a diagram illustrating an output voltage at each point in the circuit shown in FIG.

FIG. 5 is an experimental result (no reverberant sound) showing a signal input to a comparator when the piezoelectric buzzer according to the present embodiment is used.

FIG. 6 is an experimental result (with a reverberant sound) showing a signal input to a comparator when the piezoelectric buzzer according to the present embodiment is used.

FIG. 7 is an experimental result (no reverberation) showing a signal input to a comparator when a conventional condenser microphone is used.

FIG. 8 is an experimental result (with reverberation) showing a signal input to a comparator when a conventional condenser microphone is used.

[Description of code] 2 Anvil 4 Hammer 24 Forward / reverse changeover switch 30 Sound receiving unit 34 Dial setting unit 38 Microcomputer 48 Main switch