JP2627746B2 - Impact wrench tightening force control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement in an impact wrench tightening force control device.

[Conventional technology]

As shown in FIG. 11 (a), when the bolt or nut is tightened, the washer and the like are deformed as the screwing amount of the bolt is increased from the free running (a) where no axial force acts on the bolt. It gradually increases due to the repulsive force at the time, and further increases rapidly when the bolt is seated on the workpiece. The point T at which this large torque or axial force is generated is called a trigger point. Then, as the tightening is further performed from the trigger point T, the torque or the axial force of the bolt increases, and the workpiece is fastened. This is called the middle term (b). When the bolt is tightened even after the middle period, the torque or the axial force of the bolt reaches a plateau. This is called the latter period (c).

An appropriate bolt fastening force is set to a torque or an axial force in the second half of the middle period (b) to the first half of the second period (c).

The conventional torque or axial force control device automatically sets the current and frequency of the step motor when the torque applied to the volts becomes constant (trigger point). (Steps are switched to a large torque) A step motor is driven to fasten to a predetermined torque (Japanese Patent Laid-Open No. 55-70578), and a torque is controlled by the number of impacts of an impact wrench (Japanese Patent Laid-Open No. 55-70578). Japanese Patent Application Laid-Open No. 55-18350 and Japanese Patent Application Laid-Open No. 55-18350 discloses a method in which the rise (trigger point) of the torque is detected by the torque, and the tightening torque is controlled by the rotation angle of the bolt in the middle term. No. 58-71078).

[Problems to be solved by the invention]

When fastening bolts, the following situations often occur.

For example, when chips from processing of screw holes (or processing of nuts and bolts) are adhered and the bolts are seized due to this, seizure when the threads of the bolts or nuts or the screw holes are crushed, bolts and nuts Also, there is a case where the dimensions (pitch etc.) of the screw holes are incompatible and seized, or a case where the bolt is inserted obliquely and tightened (hereinafter referred to as incomplete screw fastening).

When the incomplete screw is thus fastened, torque is generated at the time of free running of the bolt (hereinafter, this torque is referred to as abnormal torque).

When such an abnormal torque occurs, the conventional torque control device has the following problems.

That is, if the torque of the bolt or the number of impacts of the impact wrench is controlled as a basic element, there is no problem because the torque and the number of impacts are zero during the free running time if the screw is normally tightened, but there is no problem. When the abnormal torque is generated by the fastening of the torque, the torque and the impact of the impact wrench caused by the torque are taken in as an element of the torque control, resulting in a large error.

For example, as shown in Japanese Patent Application Laid-Open No. 55-18350, it is confirmed that the engine is in the middle stage based on a trigger point (a predetermined torque after the rise of the torque), and the tightening torque is controlled by the rotation angle of the bolt in the middle stage. The disadvantage is that the trigger point is already shifted due to abnormal torque, and if the tightening torque is controlled with the rotation angle of the bolt based on this shifted trigger point, the tightening force will be insufficient. Having.

[Means for solving the problem]

Means according to the present invention for solving the above problem is an impact wrench having a transmission mechanism for transmitting the power of the drive shaft to a driven shaft via a hammer rotating with the drive shaft, and From the rotation angle of the rotating detection gear, a non-contact type sensor for detecting the intermittent striking motion of the hammer is provided, and the non-contact type sensor has a floating origin for each intermittent striking motion and a reverse rotation amount starting from the floating origin and When the forward rotation amount is obtained, the reverse rotation amount is sampled, and a smoothing process is performed by using a moving average method, and the smoothing reverse rotation amount is compared with a set value, and the comparison condition is not satisfied. And a first comparing means for outputting a smoothing processing instruction by a moving average method to the second comparing means, and outputting an execution command to a second comparing means when the comparison condition is satisfied, wherein the second comparing means comprises:
A parameter corresponding to an elapsed time until the first comparison means satisfies the comparison condition is compared with a set value. If the parameter does not satisfy the set value, a command to stop the tightening operation is output, and When the condition is satisfied, the floating origin at that time is output as a trigger point. The third and third steps are to obtain the rotation angle of the bolt from the number of hits after the output of the trigger point and the amount of forward / reverse rotation from the floating origin as the trigger point. A fourth comparison means is provided.

[Action]

According to the present invention, a floating origin is obtained for each intermittent striking motion of the hammer in the impact wrench, and the amount of reverse rotation (hereinafter referred to as the rebound amount) and the amount of forward rotation are measured from the floating origin.

Then, the arithmetic means samples the rebound amount and performs a smoothing process using a moving average method,
Increase the reliability of the measured rebound amount. Then, by comparing the smoothed rebound amount with the set value (hereinafter referred to as a first comparison condition), it is determined that the rebound amount at which the trigger point can be output has been reached with high reliability. I do. Here, when the first comparison condition is not satisfied, the smoothing process is repeated by the moving average method. Then, when the first comparison condition is satisfied, for example, whether or not a predetermined time has elapsed (hereinafter, referred to as a second comparison condition) is verified by the second comparison means.

Here, when the first and second comparison conditions are satisfied, the bolt fastening force has a desired strength at a desired time, which indicates that the bolt fastening is proceeding correctly. The second comparing means outputs a floating origin when the first and second comparison conditions are satisfied as a trigger point. After the output of the trigger point, the number of hits of the hammer is integrated by the third comparing means, and bolts are tightened until the integrated value reaches a predetermined number of hits. At the same time, the floating origin at the time of output of the trigger point is obtained as a starting point. The rotation angles of the bolts are obtained from the rebound amount and the normal rotation amount and accumulated in the fourth comparing means, and the bolts are tightened until the accumulated value reaches the predetermined rotation angle.

Further, when the second comparison condition is not satisfied, that is, when the first comparison condition is satisfied before the predetermined time elapses, fastening of the incomplete screw that generates abnormal torque at the free running time is performed. Judging that the state is the state, the second comparing means does not output the trigger point but outputs a command to stop the fastening operation.

According to the present invention, when the rebound amount is sampled, the rotation angle of the detection gear that rotates together with the drive shaft is detected by a non-contact sensor, so that the rotation of the drive shaft itself can be directly detected, The detection accuracy is improved by preventing noise from being mixed into the signal as much as possible. Further, even when it is difficult to prevent noise from being mixed in the detection signal, the effect is minimized by performing the smoothing process by the moving average method.

By the way, as a second comparison condition, it is also possible to compare a parameter corresponding to the elapsed time, for example, a rotation angle of a screw, a rotation angle of a socket of an impact wrench, and the like with a set value.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail.
First, basic matters necessary for the description of the embodiment will be outlined.

(1) Rebound Angle The greater the torque (hardness of screwing the impacted object) of the hammer of the impact wrench, the greater the rebound (rebound angle or amount) of the hammer.

Therefore, during the free running time when the torque is zero, the hammer of the impact wrench generally does not rebound.

In FIG. 10, the first rebound (line A) occurs when the free running time has passed and the washer or the like is deformed. That hammer occurs blows I ₀ after the rotation shown in the line A, resulting rotation of the certain amount of the bolt (or nut). Then, a reverse rotation (rebound) R ₀ occurs due to the reaction. The point at which the normal rotation is reversed to the reverse rotation is defined as a floating origin. Then, from the reverse rotation from the floating origin only rebound amount R.theta ₀ (a) point, again the operation of the hammer moves to the normal rotation. And generating a hit I ₁ after the forward rotation indicated by the line B. During the period from the rebound R ₀ to the hit I ₁ , the rotation substantially occurring on the bolt (or nut) is θ ₁ .

Next, resulting rebound R ₁ from the floating origin, hammer moves the normal rotation from the (b) point. And generating a hit I ₂ after the forward rotation indicated by the line C. Here, the rotation occurring substantially bolts (or nuts) is theta _2. Similarly, a forward rotation and an impact I ₃ ,... Shown by a line C (the third time) and a line D (a fourth time) occur, and the rebound R ₃ ,.
... occurs.

That is, the rotation angle theta _n tightening bolt (nut) is floating origin ,,, reverse rotation amount (Fig. 10) as a starting point (rebound angle) R.theta _(n-1) occurs, and further proceeds to forward rotation after occur striking I _n, bolts (or nuts) in a series of strokes that are tightened, theta _{n =} rotation angle -360 ° for hammer - rebound angle R.theta _(n-1)
... Equation (1) holds.

If the above example is applied, θ ₁ = (point (I) to point I ₁ (floating origin)) − ((a) to point (a) ′) − Rθ ₀
Next, using the rotation angle and the rebound angle R.theta ₀ hammer, it is possible to determine the clamping angle theta ₁ of the bolt.

(2) Relationship between bolt torque or axial force and rebound angle As shown in FIG. 11, there is a close relationship between the two.

That is, in equation (1), bolts and tightening rotation angle theta _n (or nut), between the rebound angle R.theta _(n-1) have a certain relationship, fastening the rotating being struck by the hammer plotting measure the torque or axial force urging the rotation angle theta _n can be obtained curve a in FIG. 11 (a). Thereby, the torque or the axial force of the bolt corresponding to the rebound angle Rθ _(n-1) can be known.

In FIG. 1, reference numeral 1 denotes an impact wrench, and reference numerals 2 and 3 denote sensors for detecting a rebound amount. 4 is an amplifying unit, 5 is a waveform shaping unit, and 6 is an input circuit. Reference numeral 7 denotes a trigger point detection unit, 8 denotes a rebound output unit, and 9 denotes a bolt rotation angle signal output unit. 10 is a bolt fastening completion detection unit,
11 is an electromagnetic valve control unit, 12 is an output circuit, and 13 is an electromagnetic valve.

First, the impact wrench 1 will be described. Solenoid valve 1
3. The air pressure-fed through the air supply valve 21 and the forward / reverse switching valve 20 is supplied to the vane 18 to rotate the rotor 19.

The hammer pin 16 rotates with the rotor 19, which is the drive shaft, and is further supported by the hammer pin 16.
Through 15, it is engaged with an anvil 17 which is a driven shaft. That is, the hammer 15 rotates together with the rotor 19, and forms a transmission mechanism that transmits the power of the rotor 19 to the anvil 17 via the hammer 15. Also, a detection gear is attached to the hammer pin 16.
The detection gear 14 rotates together with the rotor 19. In FIG. 8, 19 is a rotor, 18 is a vane, and 20 is a forward / reverse switching valve. In FIG. 9, the detection gear
Non-contact sensors 2 and 3 for detecting the amount of rebound are provided at positions facing the position 14. This sensor
7 are built in the impact wrench 1 as shown in FIG. As described above, since the detection gear 14 rotates together with the rotor 19 serving as the drive shaft, the sensors 2 and 3 directly detect the rebound amount of the rotor 19 serving as the drive shaft. Therefore, noise is prevented from being mixed into the detection signal, which is a weak point of the non-contact sensor, as much as possible, and the detection accuracy is improved.

Next, the trigger point detector 7 will be described in detail. As shown in FIG. 2, in the trigger point detecting section 7, the rebound amount detected by the sensors 2 and 3 is rebound-sampled by 22. The sampled rebound amount is subjected to smoothing processing by the arithmetic means 23 using the moving average method. Therefore, even when noise is mixed in the detection signals of the sensors 2 and 3, the influence of the noise can be minimized by the smoothing process, and the detection accuracy can be improved. Then, the smoothed rebound amount is compared with the set value by the first comparing means 24,
When the first comparison condition is not satisfied, a smoothing processing command by the moving average method is output. Then, the oldest sample is discarded, the newest sample is fetched, and the arithmetic means 23 performs averaging processing. Then, when the first comparison condition is satisfied, the second comparison means 24 'executes the first comparison means 24 to compare the second comparison condition, for example, whether a predetermined time has elapsed. Command is output. If the second comparison condition is satisfied, it is determined that the bolt has been properly tightened, and the second comparison means 2 is determined.
4 'outputs the trigger point 27. If the second comparison condition is not satisfied, it is determined that the incomplete screw in which abnormal torque is generated at the free running time is in the tightened state, and the second comparing means 24 'does not output the trigger point, and Outputs the work stop command.

More specifically, in FIGS. 5 and 6, the set values shown in FIG. 6 are measured in advance according to various conditions such as a nominal diameter, a pitch, and a length of a bolt, and an object to be fastened or a washer. The trigger point is determined in advance, and is set based on, for example, the relationship between the number of rotations of the bolt and time.

For example, when the time is set as a reference, (a) is a free running time, (a) 'is a time during which a washer or the like is deformed and seated, and the total time of (a) and (a)' is t. when you set rebound height generated from the start after t time _{(r 5 + r 6) /} 2 as a set value.

The example shown in FIG. 5 is for three cases where the sampling amounts are 39, 40, and 41. First, when n = 1 is substituted at the start, the rebound height of 39 is r ₀ , and the rebound height of 40 is
The rebound heights of r ₁ and 41 are r ₂ . The arithmetic means 42 for performing smoothing processing by the moving average method in order to average this
Is calculated, and the rebound height R subjected to the smoothing process is obtained. Then, this value is compared by the comparing means 43. Even if some noise is mixed in the detection signal of 40, the rebound height R obtained by performing the smoothing process together with the detection signals of 39 and 41 can suppress the influence of the noise, and Can be improved in the reliability of the comparison determination result.

In the case of n = 1, the setting value> R is satisfied from FIG. 6, and the comparison condition is not satisfied. Therefore, a smoothing command by the moving average method is issued.

Discard the oldest sample r ₀ on the basis of this directive, taking in new seems to sample r _3.

That is, by incrementing the counter by one and setting n = n + 1, sampling targets are r ₁ , r ₂ , and r ₃ . In this manner, the smoothing processing by the moving average method is sequentially performed.

In the case of the example of FIG. 6, the trigger point is output when the comparison condition (set value ≦ R) is satisfied for the first time at n = n + 5 and the time at this time is after t.

If an abnormal torque is generated at the times (a) and (a) ', the comparison condition is satisfied before the time t elapses, so that the incomplete bolt fastening is determined.

Next, a description will be given of a rebound output unit 8 as a third comparison unit and a rotation angle signal output unit 9 as a fourth comparison unit. The output torque of the rebound output unit 8 and the output signal of the rotation angle signal output unit 9 controls the bolt fastening torque in the middle period (after the trigger point output).

First, the rebound output unit 8 will be described with reference to FIG. In the trigger point output section 8, the input circuit 6
The rebound amount taken from (Fig. 1) is measured at 28, and the set rebound amount at the trigger point is compared with the comparison unit.
Compare at 29. Then, from the point in time when the trigger point detecting section 7 outputs that the trigger point has been reached (actually, the blow immediately before reaching the trigger point), an integrating section
Accumulate the number of hits at 30. Then, the comparing unit 31 compares the set number of hits with the set number of hits, and when the integrated number of hits matches the set number of hits, determines that the bolt fastening torque is the optimal torque and outputs the torque from the output unit 32.

The reason why the tightening force of the bolt can be determined based on the accumulated number of hits and the rebound amount is as follows. That is, as already explained FIG. 11, there is a certain relationship between the input rebound amount (angle) R.theta _n and striking I _n, rebound weight R.theta _(n-1) and the rotation angle theta _n bolts Since there is also a certain relationship (relationship of the first formula) between them, there is a correlation between the cumulative number of impacts and the torque or axial force of the bolt. Therefore, the torque or the axial force of the bolt is determined based on the integrated number of hits from the input circuit 6 and the rebound amount.

Next, the rotation angle signal output unit 9 which is a rotation angle detection means will be described with reference to FIG. As described earlier, between the rotational angle theta _n and rebound angle Rθ bolts _(n-1) there is a constant relationship (first equation relationship).

In the rotation angle signal output unit 9, the bolt rotation angle is detected by the bolt rotation angle detection unit 33 based on the rebound amount (angle) from the input circuit 6, and the trigger check unit 34 checks the trigger point. After confirming the trigger point, the bolt rotation angle accumulation section
The rotation angle of the bolt from the floating origin at the time of the trigger point output is accumulated at 35, and the rotation angle of the bolt is detected while comparing the accumulated value with the set value by the comparison unit 36.

When satisfied, the rotation angle signal is output from the rotation angle signal output unit 37, and the bolt is fastened with the optimum fastening torque.

In the present embodiment configured as described above, as shown in FIG. 1, the rotation angle of the detection gear 14 is detected by the sensors 2 and 3 so that the rotation of the rotor 19 which is the drive shaft is not adversely affected by noise. The rotation is detected, a floating origin is determined for each intermittent striking motion of the hammer, and the rebound amount of the hammer is determined starting from the floating origin.

The rebound amount detected here is taken from the input circuit 6 to the trigger point detection unit 7, rebound output unit 8, and turning axis signal output unit 9. Then, the arithmetic means of the trigger point detection unit 7 performs a smoothing process on the sampled rebound amount by the moving average method to obtain a more reliable value. Then, the first comparing means for comparing the smoothed rebound amount with the set value correctly determines whether or not the rebound amount at which the trigger point can be output has been reached. Here, when the first comparison condition is not satisfied, the smoothing process is repeated by the moving average method. Further, when the first comparison condition is satisfied, it is verified by the second comparison means whether or not a predetermined time has elapsed.
Then, a more reliable true trigger point is output.

In the rebound output unit 8 as the third comparison means, after confirming the true trigger point, the rebound output unit 8 integrates the number of hits after the trigger point output,
When the bolt reaches the optimum fastening torque, the fact is output. On the other hand, the at the rotation angle signal output section 9 is a fourth comparison means for accumulating the bolt rotation angle theta _n tightening after the true trigger point is output, the bolt has reached the optimum tightening torque Is output. When both of these outputs are satisfied simultaneously, the completion of bolting is output by the bolting completion detecting unit 10, and the solenoid valve 13 is turned off by the solenoid valve control unit 11, thereby completing the tightening.

If the bolt is tightened, the tightening torque may fluctuate within an allowable range (a slight torque fluctuation may occur due to a manufacturing error of the bolt or the like), or some noise may be mixed in the detection signals of the sensors 2 and 3. Even if it does, the torque fluctuation and noise of the bolt within the allowable range are averaged by the moving average method,
It does not become a disturbance when determining the trigger point.

In the present embodiment, the rebound amount measured from the floating origin for each intermittent striking motion of the hammer is used as a specific physical quantity serving as a criterion for determining whether to output the trigger point, and the rebound amount sampled is used. Since the reliability of the value is improved by performing the smoothing process, the output timing of the trigger point can be specified more accurately.

In the above description, rebound sampling is performed at three points, but the present invention is not limited to this.

〔The invention's effect〕

As described in detail above, according to the impact wrench tightening force control device according to the present invention, the floating origin for each intermittent striking motion of the hammer is used as the specific physical quantity serving as a criterion for determining whether to output the trigger point. The reliability of the value of the rebound amount is increased by using the rebound amount measured as (1) and smoothing the sampled rebound amount. Then, by comparing the smoothed rebound amount with the set value, it is accurately determined whether or not the rebound amount at which the trigger point can be output has been reached. Further, when the output of the trigger point becomes possible, a parameter corresponding to the elapsed time until the comparison condition is satisfied is compared with a set value to determine whether or not the bolt tightening process is correctly performed. Verify. If the first and second comparison conditions are both satisfied, the floating origin at that time is output as a trigger point. And
Further, the third and fourth comparing means accumulate the number of hits after the output of the trigger point, accumulate the rotation angle of the screw and compare it with a predetermined value, thereby obtaining an optimum tightening amount. By the way, when the second comparison condition is not satisfied,
Upon detecting the occurrence of abnormal torque during the free running time, the second comparing means does not output a trigger point. As a result, since the solenoid valve does not operate, this state can be automatically detected, for example, to detect incomplete bolt fastening.

Furthermore, in detecting the amount of rebound of the hammer,
Since the rotation angle of the detection gear that rotates together with the drive shaft is detected, the rebound amount of the drive shaft is directly detected, and as much as possible noise in the detection signal, which is a weak point of the non-contact sensor, is reduced. Prevention and detection accuracy can be improved. Further, even when noise is mixed in the detection signal, the influence of the noise can be minimized by the smoothing process, so that the detection accuracy can be improved, and the trigger point can be set with high accuracy. It becomes possible to detect.

As described above, when the trigger point is output and the solenoid valve is operated, and the impact wrench is automatically tightened and stopped, it is confirmed that no abnormal torque has been generated and the engine has been tightened with the appropriate torque. Will be.

In this manner, the fastening failure is eliminated, and the fastening torque of the bolt is automatically controlled on the basis of the true trigger point, so that high-precision fastening is possible, and the reliability of the assembled product is greatly improved. And so on.

In addition, the use of a microcomputer makes it possible to automatically judge the quality of the fastening, which makes it possible to realize an automatic assembly line using a robot and greatly improves productivity. Having.

[Brief description of the drawings]

1 to 9 show an embodiment of the present invention. FIG. 1 is a block diagram of the entire apparatus, FIG. 2 is a flowchart of a trigger point detecting section, FIG. 3 is a flowchart of a rebound output section, FIG. 4 is a flowchart of a rotation angle signal output unit, FIG. 5 is a flowchart showing a specific example of detecting a trigger point, FIG. 6 is a diagram specifically showing set values of a trigger point, and FIG. 8 is a partial vertical cross-sectional view of the impact wrench taken along line AA, FIG. 8 is a vertical cross-sectional view of the impact wrench taken along line BB in FIG. 1, and FIG. 9 is a rebound amount sensor using a detection gear. It is a perspective view of a part. 10 and 11 are explanatory diagrams, and FIG. 10 is a diagram showing the relationship between the rebound angle and the rotation angle of the bolt. In FIG. 11, (a) and (b) show the relevance, respectively. (A) is a diagram showing the relationship between the rotation angle of the bolt and the torque or axial force, and (b) is a diagram showing the relationship between the impact (number of impacts) and the rebound angle. 1 Impact wrench 2, 3 Sensor detecting rebound amount, 7 Rebound detection unit, 8 Rebound output unit, 9 Rotation angle signal output unit, 10 Bolt fastening completion detection unit , 11 ... Solenoid valve control unit, 13 ... Solenoid valve, 23
Calculation means for smoothing processing using the moving average method, 24
... first comparing means, 24 '... second comparing means.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaru Mizuhara 3-6-15 Nonogami, Habikino-shi Inside the company Kurobe Co., Ltd. (72) Inventor Takashi Kobayashi 3-6-15-1 Nonogami, Habikino-shi Co., Ltd. (56) References JP-A-58-90473 (JP, A) JP-A-61-8284 (JP, A) JP-A-60-201882 (JP, A) JP-A-59-196169 (JP, A) JP-A-59-14477 (JP, A) JP-B-61-7908 (JP, B2) JP-B-61-37505 (JP, Y2)

Claims (1)

(57) [Claims] 1. An impact wrench having a transmission mechanism for transmitting the power of a drive shaft to a driven shaft via a hammer that rotates with the drive shaft, the impact wrench comprising: a rotation angle of a detection gear that rotates with the drive shaft; A non-contact type sensor for detecting the intermittent striking motion of the hammer; a floating origin for each intermittent striking motion, and a reverse rotation amount and a forward rotation amount starting from the floating origin, which are determined by the non-contact type sensor; Calculating means for sampling the amount and performing a smoothing process using a moving average method;
The smoothed reverse rotation amount is compared with a set value, and when the comparison condition is not satisfied, a smoothing processing command by the moving average method is output, and when the comparison condition is satisfied, execution to the second comparing means is performed. A first comparing means for outputting a command, wherein the second comparing means compares a parameter corresponding to an elapsed time until a comparison condition in the first comparing means is satisfied with a set value, and When the parameter does not satisfy the set value, a command to stop the tightening work is output, and when the parameter satisfies the set value, the floating origin at that time is output as a trigger point. An impact wrench tightening force control device comprising: third and fourth comparing means for obtaining a rotation angle of a bolt from a forward / reverse rotation amount from a floating origin as a trigger point.