JPH0691551A - Impact type screw fastening device - Google Patents

Abstract

PURPOSE:To improve fastening force control by carrying out computation on an increase quantity of fastening force with every impact after a peak value of a torque pulse is found from detected torque, finding deviation from target fastening force, and carrying out cutoff control after the motive power source cutoff timing is determined according to eccentricity when being judged that the target fastening force can be obtained at the next impact. CONSTITUTION:A signal outputted by a torque detecting part of an impact wrench body 10 is inputted to a torque signal processing part 32 of a torque control device 30, and is converted into a torque signal, and is inputted to a peak value processing part 33. The peak value processing part 33 extracts and stores a peak value of a torque pulse, and a fastening force computing part 35 reads out a coefficient to torque equivalent to an increase in fastening force from a fastening force data memory part 34, and carries out operation on equivalence of the increase in the fastening force. A short fastening force computing part 361 finds deviation between present state fastening force and target fastening force. Upon judgment that the target fastening force can be obtained at the next impact, a valve closing timing computing part 362 closes a valve of the impact wrench body 10 at the prescribed timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention utilizes impact force to
For screw tightening devices that perform screw tightening work, such as impact wrenches and impact type nuts and runners,
In particular, the present invention relates to a technique for controlling the fastening force (tightening force) of a screw.

[0002]

2. Description of the Related Art As a conventional impact wrench for controlling tightening torque, there is, for example, a device described in Japanese Utility Model Application No. 3-12370. FIG. 19 is a sectional view of the above device. In FIG. 19, the main shaft 15 is made of a material having a magnetostrictive effect. Then, a change in torque is detected by detecting a change in magnetic permeability on the surface of the main shaft 15 that accompanies a torque pulse generated at the time of bolt fastening as a change in inductance of the detection coils 26a and 26b of the torque detection unit 11. Then, when the detected torque reaches a value within a predetermined range, a control signal from the control circuit 120 causes
Shut off valve 12 is closed and air motor unit 1
The compressed air to 3 is cut off, and thereby the driving of the hydraulic pressure pulse generator 14 and the main shaft 15 is stopped. However, when tightening a screw with a torque wrench such as a taper beam wrench, the tightening torque and the tightening force generated in the tightening part are in a proportional relationship. The peak value of is not proportional to the fastening force. For example, it is frequently observed that the fastening force increases even when a torque pulse with a smaller peak value than the immediately preceding torque pulse occurs. It turned out. in this way,
Since the peak value of the torque pulse cannot be said to correspond to the fastening force on a one-to-one basis, the fastening force cannot be accurately detected even if this peak value is accurately detected.
Even if the shut-off valve is cut-off controlled based on this, it does not mean that the fastening force is accurately controlled. As described above, in the conventional device, the fastening force could not be accurately detected.
There is a problem that it is difficult to accurately control the desired fastening force.

In order to solve the above problems, the applicant has
An application has already been filed for a device that calculates the amount of increase in fastening force for each impact using the peak value of the instantaneous torque at the time of screw fastening (“impact screw fastening device” filed on August 28, 1992: undisclosed) ). FIG. 20 is a flowchart of calculation in the device. The mechanical portion is the same as that shown in FIG. As shown in FIG. 20, this device calculates the increase amount of the fastening force for each impact using the peak value of the instantaneous torque at the time of screw fastening, and when the value reaches a predetermined fastening force, By shutting off the compressed air supplied to the impact wrench, the target fastening force is obtained.

A detailed description will be given below with reference to FIG.
First, in step S1, the value of the target fastening force cFc (indicated as cut-off fastening force in the figure) is determined. Next, in step S2, the value of the fastening force up to that point is reset.
F (0) = 0. Next, in step S3, fastening is started. Further, steps S4 to S8 form a loop, and the calculation is performed each time a shock is applied. First, in step S4, the peak value T _P (i) of the torque pulse is obtained from the signal of the torque sensor and stored.
Next, in step S5, the coefficient C _TF (i) for the torque of the increase in the fastening force at F (i-1) is calculated based on the table of the fastening force data memory unit. However,
_CTF (i) = _CTF [F (i-1)]. Next, step S6
Then, the increase δF (i) of the fastening force due to the impact is calculated. However, δF (i) = C _TF [F (i−1)] × T
_P (i). Next, in step S7, the fastening force F after the impact is applied.
Calculate (i). However, F (i) = F (i-1) +
δF (i). Next, in step S8, it is determined whether or not the fastening force F (i) after impact is equal to or greater than the target fastening force cFc, and NO
If so, the process returns to step S4 and steps up to step S8 are repeated. On the other hand, if YES in step S8, the process proceeds to step S9, at which point a cutoff command is issued. This causes the compressed air valve to close. Next, in step S10, it is determined whether or not to end the process. If YES, the process ends, and if NO, the process returns to step S2 to perform the next screw tightening. 21 and 22 are operation characteristic diagrams in the above control, FIG. 21 is a diagram showing an example of a peak value of torque at each impact, and FIG. 22 is a diagram showing a relationship between the number of impacts and an increase in fastening force. Is. In addition, the above-mentioned conventional example and the description of the prior art of the applicant are as follows.
Although an impact wrench has been described as an example, the same applies to an impact type nut runner and the like.

[0005]

As described above, as shown in FIG.
In the conventional device shown in FIG. 2, since the fastening force cannot be detected accurately, there is a problem that it is difficult to accurately control the fastening force to a desired one. Further, in the prior invention of the present applicant made to solve the above problems, the fastening force can be detected, but the fastening force increases stepwise (stepwise) each time the impact is given. Therefore, there is a problem that it is impossible to control a minute value equal to or smaller than one increment. For example, referring to the example of FIG. 22, when the target value of the fastening force is 25 kN, the amount of increase in the fastening force due to one impact is about 3 kN, so about 12% of the target value cannot be controlled. It became a range, and it was not possible to precisely control even minute values.

The present invention has been made in order to solve the problems of the prior art as described above and to further improve the prior art of the present applicant. It is possible to precisely control the fastening force and the accuracy is high. An object is to provide an impact type screw tightening device capable of performing screw tightening work.

[0007]

In order to achieve the above object, the present invention is constructed as described in the claims. That is, in the invention according to claim 1, a drive means having a pulse component in the drive output, a joint part with a screw at one end, and a main shaft for tightening the screw when driven by the drive means, An impact type screw tightener main body having a shutoff means for shutting off a power source applied to the drive means and a torque detection means for detecting a torque change of the main shaft, and a torque pulse obtained from the detection result of the torque detection means. The peak value of is used to calculate the increase amount of the fastening force for each impact, the deviation between the current fastening force and the target fastening force is calculated, and when it is determined that the target fastening force will be reached by the next impact, And a control means for calculating a timing for shutting off the power source to the drive means according to the deviation and controlling the shutoff means according to the result. The impact type screw tightener body corresponds to, for example, the impact wrench body 10 in the embodiment shown in FIG. 1, which will be described later. Similarly, the drive means is connected to the air motor section 13, the main shaft is connected to the main shaft 15, and the main shaft 15 is disconnected. The means corresponds to the shut-off valve 12, and the torque detecting means corresponds to the coils 26a and 26b. The control means corresponds to, for example, the torque control device 30 in the embodiment shown in FIG. 4 described later.

Further, in the invention described in claim 3,
A drive means having a pulse component in a drive output, a joint portion with a screw at one end, for tightening the screw by being driven by the drive means, and a level of a power source applied to the drive means are lowered. For each impact, the impact type screw tightener main body having the adjusting means and the torque detecting means for detecting the torque change of the spindle is used, and the peak value of the torque pulse obtained from the detection result of the torque detecting means. The amount of increase in the fastening force is calculated, the deviation between the current fastening force and the target fastening force is calculated, and when the above deviation falls below a predetermined value, the adjusting means is driven to lower the level of the power source. And a control means for controlling. The impact type screw tightener main body corresponds to, for example, the impact wrench main body 40 in the embodiment shown in FIG. 10 described later, and similarly, the drive means is the air motor unit 13.
The main shaft is the main shaft 15, and the adjusting means is the pressure relief valve 4.
1 or the pressure detecting valve 45 of FIG. 16, the torque detecting means corresponds to the coils 26a and 26b. Further, the control means corresponds to, for example, the torque control device 42 in the embodiment shown in FIG. 11 described later.

[0009]

According to the experiments conducted by the present inventor, in the screw tightening work using the pulsed torque, there is a predetermined relationship between the change in the peak value of the torque and the change in the tightening force (tightening force). found. The present invention utilizes the above relationship, and uses the peak value of the torque pulse,
The amount of increase in fastening force is calculated for each impact.
In the invention according to claim 1, the deviation between the current fastening force and the target fastening force is obtained, and when it is determined that the target fastening force is reached due to the next impact, the driving means is driven according to the above-mentioned deviation. The power source is shut off at a predetermined time by calculating the timing of shutting off the power source and controlling the shutoff means according to the result. Therefore, the increase amount of the fastening force at the last impact is adjusted so as to match the amount that is just short, so that the target fastening force can be accurately controlled. Also,
In the invention according to claim 3, when the deviation becomes equal to or less than a predetermined value, that is, when the actual fastening force approaches the target fastening force, the adjusting means is driven to lower the level of the power source. It is configured to let. Therefore,
When the actual tightening force approaches the target tightening force, the amount of increase in the tightening force due to one impact becomes small, and it approaches the target tightening force in small steps. Can be precisely controlled.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 are views showing a first embodiment of the present invention, FIG. 1 is a sectional view of an impact wrench body, and FIG. 2 is A of FIG.
-A sectional view, FIG. 3 is a block diagram of the atmospheric pressure circuit in FIG. 1, FIG. 4 is a block diagram of the torque control device 30 in FIG. 1, and FIG. 5 is a flowchart showing a calculation process.

First, in FIG. 1, 10 is an impact
The impact wrench body 10 is provided with an air supply unit 16, an air motor unit 13, a hydraulic pressure pulse generation unit 14, and a torque detection unit 11 in the impact wrench body 10. Air supply unit 16, air motor unit 13, hydraulic pulse generation unit 14
The air supply unit 16 has an air passage 17 communicating with the air motor unit 13, and a main valve 18 and a switching valve 19 are provided in this order in the air supply unit 16. The main valve 18 is opened by pulling the valve operating lever 20, and the switching valve 19 is opened by turning the rotation switching lever 21 to a predetermined rotation position. The air motor unit 13 includes a rotary drive shaft 22 arranged in an eccentric cylinder,
The rotary drive shaft 22 is rotated by the compressed air acting on the vanes 23. The hydraulic pressure pulse generator 14 is a main shaft 15 provided in a liner case 24 directly connected to the rotary drive shaft 22 of the air motor unit 13.
And a driving blade 25 that is mounted on the main shaft 15, and the liner case 24 is filled with oil liquid. The main shaft 15 has a driving blade 25 and an inner surface of the liner case 24 when there is no load above a certain level.
When the load exceeds a certain level, the hydraulic pressure applied to the inner surface of the driving blade 25 via the relief valve 28 fluctuates to cause an impulsive rotation. It is like this. The tip of the main shaft 15 is shaped so as to be connected to a screw through a socket (box / wrench), and the screw can be tightened by adjusting the tip to a desired screw. Torque detector 1
1 is arranged around the main shaft 15 and has an impact
A pair of coils 26a, 26 fixed to the wrench body 10
b. The main shaft 15 is made of a material having a magnetostrictive effect in which a pair of left and right groove rows 27a and 27b having different spiral angles are provided, and coils 26a and 26b are arranged so as to face the groove rows 27a and 27b. There is. Then, by the coils 26a and 26b, the main shaft 15
The torque that acts on the can be detected. The breaker groove for the compressed air has a known structure, and 12 is a shut-off valve for supplying / cutting off the compressed air sent to the air motor unit 13. The shutoff valve 12 connects the switching valve 19 and the air motor unit 13. It is provided in the middle of the air passage to communicate with.

Next, the cross-sectional view taken along the line AA shown in FIG. 2 shows the structure of the shut-off valve 12. In FIG. 2, 52 is an electromagnetic solenoid type pilot valve,
Reference numeral 53 is an electromagnet, and the shut-off valve 12 is controlled to open and close by the operation of the pilot valve 52.

Next, FIG. 3 shows the atmospheric pressure circuit configuration in FIG. In FIG. 3, the air from the intake source 55 rotates the air motor unit 13 through the main valve 18, the switching valve 19 and the shut-off valve 12 which are opened by pulling the valve operating lever 20. The pilot valve 52 is connected to the coil 26.
Based on the detection signals of a and 26b, it is opened by a valve cut command sent from the controller 30. When the pilot valve 52 is opened, the shut-off valve 12 cuts off the supply of air to the air motor section 13.

Next, as shown in FIG. 4, a torque control device 30 electrically connected to the impact wrench body 10.
Is a torque signal processing unit 32 that produces a torque signal by inputting a signal emitted from the torque detection unit 11, a peak value processing unit 33 that extracts each peak value of an individual torque pulse from the torque signal, and a fastening force calculation unit. 35, a fastening force data memory unit 34 in which a function indicating the relationship between the coefficient for the torque of the increased fastening force (strictly speaking, the peak value of the torque pulse) and the fastening force is recorded, and the calculated fastening force. A valve control unit 36 that determines whether the force is within an appropriate range and sends an opening / closing control signal to the shut-off valve 12.
Further, the valve control unit 36 includes an insufficient fastening force calculation unit 361 and a valve closing timing calculation unit 362.

FIG. 6 is a diagram showing an example of a function recorded in the fastening force data memory section 34. As shown in FIG.
When a torque having a certain peak value is applied and the fastening force at that time is small, the amount of increase in the fastening force due to this applied torque is large, while the fastening force of a considerable level has already been generated. It can be seen that, when the torque is at the same peak value, the amount of increase in the fastening force added due to this is not large when the torque is the same. The specific value differs depending on the combination of the bolt, the tightened body, and the impact wrench. Such coefficient data is prepared as a function for each combination of the bolt to be used with the impact wrench and the object to be fastened. As will be described later, the fastening force calculator 35 calculates the fastening force based on the peak value and the function data. Further, the torque signal processing unit 32 of the torque control device 30 is adapted to obtain a final analog output by subjecting the torque signal voltage obtained from the torque detection unit 11 to sample and hold processing with a constant phase of a sine wave. This is possible because the phase of the torque signal waveform has a constant difference with respect to the phase of the excitation current waveform that does not depend on the torque value, as shown in FIG. Here, as a means for realizing this, in a section in which the phase and the voltage between the minimum value phase θ _A and the maximum value phase θ _B when the exciting current is taken out as a voltage have a one-to-one correspondence,
A circuit that performs sample hold processing of the torque signal voltage at the phase θ _S by setting the voltage value V _S is used.

Next, the operation of the first embodiment will be described based on the flow chart shown in FIG. When the valve operating lever 20 shown in FIG. 1 is pulled, the air motor unit 1 is supplied from the air supply unit 16 via the shut-off valve 12.
The rotary drive shaft 22 of the air motor unit 13 is rotated by the compressed air sent to the motor 3, and the rotational force thereof is converted into a shocking rotational force in the hydraulic pressure pulse generator 14 and transmitted to the main shaft 15 to cause the screw to rotate. Tightening work is performed. First, in step S11 of FIG. 5, the value of the target fastening force cFc (indicated as cut-off fastening force in the figure) is determined. Next, step S
12, the fastening force F is set to 0 as the initial state of the fastening start.
Reset to. Next, in step S13, screw tightening is started. In addition, steps S14 to S1
Reference numeral 9 forms a loop, and calculation is performed each time a shock is applied. First, in step S14, the peak value processing unit 33 extracts the peak value T _P (i) of the torque pulse from the plurality of sample and hold values obtained by the torque signal processing unit 32, and stores it. Next, in step S15, the coefficient C _TF (i) for the torque corresponding to the increase in the fastening force at F (i-1) is read from the fastening force data memory unit 34. However, C _TF (i) = C
_TF [F (i-1)]. Next, in step S16, the increase amount δF (i) of the fastening force due to the impact is calculated. However,
δF (i) = C _TF [F (i−1)] × T _P (i). Next, in step S17, the fastening force F (i) after impact is calculated. However, F (i) = F (i−1) + δF (i). Next, in step S18, the difference between the target fastening force cFc and the current fastening force F (i) obtained in step S17 is calculated,
_{Let the} insufficient fastening force be F _N (i). However, F _N (i)
= CFc-F (i). Next, in step S19, it is determined whether or not the insufficient fastening force F _N (i) is likely to reach the target fastening force cFc in the next blow. Basically, this determination is made on the assumption that the next blow increases the fastening force by the same δF (i) as the previous one. Therefore, the determination formula in step S19 may be determined as F _N (i) ≦ δF (i). However, in reality, since the increase is about 0.7 to 0.9 times δF (i), the judgment formula is F _N (i)
≦ 0.8 × δF (i) may be used. If NO in step S19, that is, if it is determined that the target fastening force will not be reached by the next blow, the process returns to step S14.
On the other hand, if YES, that is, if it is determined that the target fastening force will be reached in the next blow, control is performed in step S20 and subsequent steps to determine when to shut off the compressed air that drives the impact wrench.

FIG. 8 is a characteristic diagram showing the relationship between the timing of shutting off compressed air and the amount of increase in fastening force. In FIG.
The abscissa represents the time from the time when the impact is applied to the time when the compressed air is cut off in milliseconds (ms), and the ordinate represents the increase amount of the fastening force in Newton (N). As can be seen from FIG. 8, the increase of the fastening force can be controlled by controlling the timing of shutting off the compressed air. The above control specifically uses the characteristics of the cut-off timing T _d as shown in FIG. That is, the delay time from the completion of the calculations from step S14 to step S20 (set to, for example, 5 ms) and the delay time from when the signal is sent to the shut-off valve 12 until the compressed air is actually shut off (10 ms). Degree) and the total delay time T ₀ is the intersection with the vertical axis, and the slope is T _c
From the insufficient fastening force F _N (i) at that time, the time T _d until the compressed air is shut off after the impact is applied is obtained. That is, in step S20, T _d = T _c × F _N (i) +
Calculate T ₀ .

Next, in step S21, it is judged whether or not the actual elapsed time t has reached the time _Td , and when the time t reset immediately after the previous impact reaches t> _Td , step S22. Then, an opening / closing control signal for shutting off the compressed air supply is sent from the valve control unit 36 to close the shut-off valve 12. This completes the screw tightening. Next, in step S23, it is determined whether or not to end the process. If YES, the process ends, and if NO, S1.
Return to 2 and tighten the next screw. As described above, in the present embodiment, the difference between the target fastening force and the current fastening force is
It is configured so that it is determined each time a shock is applied, that the next shock will reach the target shock force, and the timing for shutting off the compressed air is determined according to the lacking fastening force at that time. , The screw can be tightened precisely up to the target tightening force.

Next, FIGS. 10 to 13 are views showing a second embodiment of the present invention. FIG. 10 is a sectional view of the impact wrench body, FIG. 11 is a block diagram of the torque control device 42, and FIG.
2 is a block diagram of the atmospheric pressure circuit, and FIG. 13 is a flow chart showing the arithmetic processing. The impact wrench body 40 shown in FIG. 10 is basically the impact wrench body 40 shown in FIG.
It is the same as the wrench body 10 and is different only in that a pressure relief valve 41 is provided. This pressure relief valve 4
1 has the effect of reducing the applied air pressure by a predetermined amount when it opens. Further, in the torque control device 42 shown in FIG. 11, the torque signal processing unit 32, the peak value processing unit 33, the fastening force calculation unit 3
5 and the portion of the fastening force data / memory unit 34 are the same as those of the torque control device 30 shown in FIG. 4, but the valve control unit 43 is different. This valve control unit 4
3 is a target value approach detection unit 431 and a target value excess detection unit 43.
2 and.

The operation of this embodiment will be described below with reference to the flow chart shown in FIG. In FIG. 13, steps S31 to S37 are the same as steps S11 to S17 in the flowchart of FIG. Next, in step S38, the target fastening force cF
c is compared with the current fastening force F (i) obtained in step S37 to determine whether the fastening force F (i) is close to the target fastening force cFc. Specifically, if the fastening force F (i) is 80% or more of the target fastening force cFc, it is determined to be close. However, when the capacity of the screw tightening device is considerably larger than the target fastening force, a lower ratio, for example, 60% of the target fastening force is used.
You may comprise so that it may judge even if it is about%. If NO in step S38, the process returns to step S34 to repeat the above process. If YES, the process goes to step S39. In step S39, a pressure relief valve opening signal is sent from the target value approach detection unit 421 to the pressure relief valve 41 in FIG. 10 to open it. When the pressure relief valve 41 opens, the air pressure of, for example, 0.7 MPa, which had been applied to the air motor portion of the impact wrench until then, drops to 0.4 MPa. Since this air pressure determines the speed of acceleration of the air motor after giving one impact, the impact energy after the next time will decrease and the amount of increase in the fastening force per impact will decrease. FIG. 14 is a characteristic diagram showing the relationship between the number of impacts and the peak value of torque at the moment when the impact is applied, and FIG. 15 is a characteristic diagram showing the relationship between the number of impacts and the fastening force. As shown in FIG. 14 and FIG. 15, when the actual fastening force approaches the target fastening force and the pressure relief valve 41 is opened, the peak value of torque in one impact is reduced and the amount of increase in fastening force is small. I see. Next, in step S40, it is determined whether or not the fastening force F (i) has reached the target fastening force cFc. If it has, the cut-off command is issued in step S41. Specifically, the shutoff valve closing signal is sent from the target value excess detection unit 422 to the shutoff valve 12. This completes the screw tightening work, but if the screw tightening work is to be continued, the pressure relief valve 41 is closed and the shut-off valve 12 is opened to start the next screw tightening work.

16 and 17 are diagrams showing a third embodiment of the present invention. FIG. 16 is a block diagram of a pneumatic circuit,
FIG. 17 is a flowchart showing the arithmetic processing. As can be seen by comparing FIG. 16 with the air pressure circuit of FIG. 12, this embodiment shows that the pressure relief valve 4 of the second embodiment is the same.
1 is replaced with the pressure adjusting valve 45. The pressure adjusting valve 45 is, for example, an electromagnetic proportional relief valve. In addition, the flowchart of FIG. 17 mainly includes step S5.
Only the part 9 is different, and other parts are the same as those in the flowchart of FIG. That is, when the current fastening force is close to the target fastening force, the set pressure of the pressure adjusting valve 45 is adjusted in step S59. This set pressure P
Set _ACT (air pressure applied to the motor part of the impact wrench) to a smaller value as it approaches the target tightening force. For example, if the air pressure of the air source is represented by P _ORG , the set pressure P _ACT is given by the following equation. P _ACT = P _ORG [2-1.5 × F (i) / cFc] As described above, when the air pressure applied to the motor part of the impact wrench is reduced, the air pressure after one impact is applied. The acceleration of the motor becomes slower, the impact energy after the next time decreases, and the increase of the fastening force per impact decreases. In the flowchart of FIG. 17, when the screw tightening work is completed and the next screw tightening work is continued, the pressure adjusting valve 45 is returned to the initial state, and the shut-off valve 12 is opened before the step. Return to 52.
In this embodiment, since the impact energy amount is gradually reduced as the fastening force increases, the screw tightening work can be performed with high accuracy without increasing the tightening work time.

As described above, in the first to third embodiments, based on the known tightening force and the torque coefficient for the increase of the tightening force corresponding to the combination of the bolt, the fastened body and the impact wrench. , The torque force peak value is used to calculate the increase amount of the fastening force, and the fastening force given by the impact wrench body is calculated by repeatedly adding the increments. You can ask well. Then, by controlling the drive of the impact wrench body based on this calculation result, the actual fastening force can be made extremely close to the target value, and highly accurate screw tightening can be performed.
And the coefficient for the torque of the increase of the fastening force is
Since the impact wrench body is obtained in advance in correspondence with the combination of the main body of the impact wrench, the bolt, and the object to be fastened, if this is memorized for each combination, the fastening force data / memory unit 24 is matched to the work target. By simply switching the data to be pulled from, a highly accurate fastening force can always be obtained.

Further, in the above-mentioned embodiments, the impact wrench has been described as an example, but the present invention is not limited to this, and may be applied to an impact type nut runner or the like. For example, at present, when fastening the suspension assembly to the vehicle body, a plurality of gusset bolts are used to simultaneously tighten the multi-axis nut runners. The configuration may be as shown in. FIG.
FIG. 12 is a diagram showing a configuration of a nut / runner main body, and a torque control device has a configuration similar to that of FIG. 4 or FIG. 11. In FIG. 11, 71 is a motor, and 7
Reference numeral 2 is a torque pulse generator that generates a torque pulse as the motor 71 rotates. Further, 73 is a rotating shaft, and 74 is a tightening socket. Reference numeral 75 denotes a torque detection unit, which has the same configuration as the torque detection unit 11 shown in FIG. By using the nut runner as described above, the fastening force of each gusset bolt can be accurately set to a predetermined fastening force, as in the above embodiment.
Accurate screw tightening with little variation can be performed.

[0024]

As described above, according to the first aspect of the present invention.
In the invention described in, the peak value of the torque pulse is used to calculate the increase amount of the fastening force for each impact, the deviation between the current fastening force and the target fastening force is calculated, and the target fastening force is determined by the next impact. When it is determined that the power supply to the drive means is shut off in accordance with the above deviation, the amount of increase in the fastening force at the final impact is just insufficient. The tightening force of the screw can be controlled accurately because it is adjusted to match the amount that the screw is attached. Further, in the invention described in claim 3, when the actual fastening force approaches the target fastening force, the adjusting means is driven to lower the level of the power source. When the tightening force approaches the target tightening force, the amount of increase in the tightening force due to one impact decreases, and the tightening force approaches the target tightening force in small steps. Can be controlled. Further, in the conventional screw tightening device having a large screw tightening ability, it is extremely difficult to control the tightening force when tightening a small screw as compared with the capability. However, in the device of the present invention, the actual tightening force is tightened. When the force approaches the target tightening force, the increase of the tightening force is controlled to be small.Therefore, many excellent effects such as accurate screw tightening work can be performed even with a relatively small screw as described above. To be

[Brief description of drawings]

FIG. 1 is a sectional view of an impact wrench body 10 according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a block diagram of a pneumatic circuit in the first embodiment.

FIG. 4 is a block diagram of a control device 30 according to the first embodiment.

FIG. 5 is a flowchart showing a calculation process in the first embodiment.

FIG. 6 is a characteristic diagram showing a relationship between a fastening force and a coefficient with respect to a torque of an increase in the fastening force.

FIG. 7 is a characteristic diagram showing a relationship between a torque signal waveform and an exciting current.

FIG. 8 is a characteristic diagram showing a relationship between a cutoff time of compressed air and an amount of increase in fastening force.

FIG. 9 is a characteristic diagram showing the relationship between the deviation between the target fastening force and the current fastening force and the time Td until the compressed air is shut off.

FIG. 10 is a sectional view of an impact wrench body 40 according to a second embodiment.

FIG. 11 is a block diagram of a torque control device 42 according to a second embodiment.

FIG. 12 is a block diagram of a pneumatic circuit according to a second embodiment.

FIG. 13 is a flowchart showing arithmetic processing according to the second embodiment.

FIG. 14 is a characteristic diagram of a peak value of torque.

FIG. 15 is a characteristic diagram showing the relationship between the number of impacts and the fastening force.

FIG. 16 is a block diagram of a pneumatic circuit according to a third embodiment.

FIG. 17 is a flowchart showing arithmetic processing according to the third embodiment.

FIG. 18 is a diagram showing an embodiment in which the present invention is applied to an impact type nut runner.

FIG. 19 is a cross-sectional view of an impact wrench body in the applicant's prior application.

FIG. 20 is a flowchart showing a calculation process in the above prior application.

FIG. 21 is a characteristic diagram of a peak value of torque.

FIG. 22 is a characteristic diagram showing the relationship between the number of impacts and the fastening force.

[Explanation of symbols]

10 ... Impact wrench body 33 ... Peak value processing unit 11 ... Torque detection unit 34 ... Fastening force data / memory unit 12 ... Shut off valve 35 ... Fastening force calculation unit 13 ... Air motor unit 36 ... Valve control unit 14 … Hydraulic pressure pulse generator 361… Insufficient tightening force calculator 15… Spindle 362… Valve closing timing calculator 16… Air supply unit 40… Impact wrench body 17… Air passage 41… Pressure relief valve 18… Main valve 42… Torque Control device 19 ... Switching valve 43 ... Valve control unit 20 ... Valve operating lever 431 ... Target value approach detection unit 21 ... Rotation switching lever 432 ... Target value excess detection unit 22 ... Rotation drive shaft 45 ... Pressure adjusting valve 23 ... Vane 53 ... Electromagnet 24 ... Liner case 55 ... Intake source 25 ... Driving blade 71 ... Motor 26a, 26b Coil 72 ... torque
Pulse generators 27a, 27b ... Groove array 73 ... Rotating shaft 28 ... Relief valve 74 ... Tightening socket 30 ... Torque control device 75 ... Torque detection unit 32 ... Torque signal processing unit 52 ... Electromagnetic solenoid pilot valve

Claims (5)

[Claims] 1. A drive means having a pulse component in a drive output, a main shaft for fastening a screw by being driven by the drive means, having a joint portion with a screw at one end, and a power source applied to the drive means. Shutting off means for shutting off
An impact type screw tightener main body having a torque detection means for detecting a torque change of the main shaft, and a peak value of the torque pulse obtained from the detection result of the torque detection means are used to increase the fastening force for each impact. Calculate the amount, find the deviation between the current fastening force and the target fastening force,
When it is determined that the target fastening force will be reached due to the next impact, the control means for calculating the timing for shutting off the power source to the drive means according to the deviation and controlling the shutoff means according to the result. And an impact type screw tightening device. 2. The power source is compressed air, and the shut-off means is a shut-off valve for compressed air.
Impact type screw tightening device described in. 3. A drive means having a pulse component in a drive output, a main shaft for fastening a screw by being driven by the drive means, having a joint portion with a screw at one end, and a power source applied to the drive means. Of the impact type screw tightening machine having an adjusting means for lowering the level of the torque and a torque detecting means for detecting the torque change of the main shaft, and the peak value of the torque pulse obtained from the detection result of the torque detecting means is used. Then, the increase amount of the fastening force is calculated for each impact, and the deviation between the current fastening force and the target fastening force is calculated.
An impact type screw tightening device comprising: a control unit that drives the adjusting unit to reduce the level of the power source when the deviation becomes equal to or less than a predetermined value. 4. The power source is compressed air, and the adjusting means is a compressed air relief valve.
Impact type screw tightening device described in. 5. The impact type screw tightening device according to claim 3, wherein the power source is compressed air and the adjusting means is a pressure adjusting valve.