JP2006015438A - Impact fastening tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an impact fastening tool which can correctly carry out determination of a fastening torque without being affected by erroneous strike detection. <P>SOLUTION: The impact fastening tool is formed of an impact mechanism for applying a strike by a hammer rotatively driven by a motor, to an output shaft, a strike detecting means for detecting a striking action by the impact mechanism, based on a variation of a rotational speed detected by a rotational speed detecting means, and a torque estimating means for calculating a value of the fastening torque, based on a striking interval detected by the strike detecting means and a rotational angle rotating during the striking interval detected by a motor rotational angle detecting means. Then a motor control means of the impact fastening tool terminates the motor when an estimated torque value estimated by the torque estimating means reaches a predetermined value. Further the impact fastening tool is comprised of a striking validity determining means for inhibiting torque estimating operation by the torque estimating means, based on a strike that does not satisfy predetermined conditions out of strikes detected by the strike detecting means. According to the operation of the impact fastening tool, if abnormality occurs during its striking action, the estimated torque operation is not executed, and therefore erroneous determination that the estimated torque value reaches the set value, is not made, whereby the tool does not terminate its operation in the process of screw fastening. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an impact tightening tool that performs a tightening operation using impact impact such as an impact driver or an impact wrench.

  The impact tightening tool with impact mechanism that repeatedly impacts the engagement between the hammer driven by the motor's deceleration output and the anvil provided on the output shaft, has good workability such as high speed rotation and high torque. Although it is widely used in construction sites and assembly factories, it is necessary to obtain the tightening torque when controlling the motor to stop when the tightening torque reaches a preset torque with an impact tightening tool. The present applicant has proposed a method for estimating the calculation of the tightening torque from the rotational speed of the motor and the amount of motor rotation between hits.

The above tightening torque estimation method is derived from the relationship between the balance of kinetic energy for each impact, that is, the energy given to the anvil of the output shaft by hammering and the energy consumed by tightening is approximately equal. Briefly, the rotation angle θ and the tightening torque T after the screw tightened by the impact tightening tool can be expressed by a function T = τ (θ) as shown in FIG. If θ1... ΘN in the figure is the rotation angle of the anvil at the time of hitting the hammer with the anvil (output shaft rotation angle), the value E _{1 obtained} by integrating the function τ in the interval [θ ₁ , θ ₂ ]. Is the energy consumed for the tightening operation, and is equal to the energy given to the anvil by the blow generated at the θ ₁ point. Therefore, the average torque <Tn> in the section [θ _{n + 1} , θ _n ] is given by the energy En and the rotation angle Θn: (θ _{n + 1} −θ _n ) between hits.
<Tn> = En / Θn (1)
It can be asked.

In order to perform the tightening torque control, the driving of the motor may be stopped when the obtained average torque <Tn> becomes equal to or higher than the set torque Ts. The energy En is the rotation speed (motor rotation angle between striking intervals / striking interval) ωn and the known anvil moment of inertia Ja.
En = 1/2 × Ja × ωn ² (2)
And θ can be easily obtained by the rotation angle detecting means.

  Here, Japanese Patent Laid-Open No. 2001-246573 discloses that the tightening torque is obtained by the method represented by the above formula (1), and that a microphone or the like is used as the hit detection means, and the hit detection omission is omitted. It is stated that the accuracy of torque estimation can be improved by correcting the motor rotation amount between hits and estimating the average torque for erroneous hit detection.

On the other hand, the hit detection can be performed based on the amount of change in the rotational speed. In this case, the impact detection can be performed without requiring a dedicated member for impact detection. However, when the impact detection based on the amount of change in the rotational speed is performed, the rotational speed at the time of tapping, etc. In many cases, it is determined that the change is caused by the impact. In this case, if the average torque is estimated by correcting the motor rotation amount between impacts, the tightening torque is calculated by calculating the incorrect average torque. Although the set torque is not reached, it is determined that the set torque has been reached and the frequency at which the motor is stopped increases.
JP 2001-246573 A

  The present invention has been invented in view of the above-described conventional problems, and an object of the present invention is to provide an impact tightening tool capable of more accurately performing tightening torque determination without being affected by erroneous hit detection. The issue is to provide.

  In order to solve the above-mentioned problems, an impact tightening tool according to the present invention includes an impact mechanism that applies an impact to a output shaft by a hammer that is rotationally driven by a motor, motor control means that controls rotation and stop of the motor, Rotation angle detection means for detecting the rotation angle of the motor, rotation speed detection means for detecting the rotation speed of the motor, and a striking action by the impact mechanism are detected from the amount of change in rotation speed detected by the rotation speed detection means. The torque estimation means comprises: a hit detection means; and a torque estimation means for calculating a tightening torque from a rotation angle between the hit interval detected by the hit detection means and a hit interval detected by the motor rotation angle detection means. Impact tightening in which the motor control means stops the motor when the estimated torque value estimated by the motor reaches a predetermined value In ingredients, among striking detected by the strike detection unit, it is characterized in further comprising a striking correctness determination means not to perform the torque estimation calculation of a torque estimating means based on the blow does not satisfy the predetermined condition. If the hammering operation is abnormal, the estimated torque calculation is not performed (the calculation result is not adopted), so it is not determined that the set torque has been reached by mistake, and there is no possibility of stopping during screw tightening. Is.

  As the hitting correctness determination means, among the hits detected by the hit detection means, hits when the hit interval is not less than a predetermined time and / or less than a predetermined time are not determined as hits, and hits detected by the hit detection means Among the hits detected by the hit detection means, the hit interval detected this time and the previous detection are not detected as hits when the difference between the hit interval detected this time and the hit interval detected last time is equal to or longer than a predetermined time. Among the hits detected by the hit detection means, the rotation angle of the motor during the hit interval is greater than or equal to the predetermined angle and the hit is not determined to be hit when the difference from the hit interval is not less than the predetermined time and not more than the predetermined time. Or, when the impact is less than a predetermined angle, the impact is not determined as an impact, and further, the impact detected when the motor applied voltage applied to the motor by the motor control means is less than the prescribed applied voltage value. Can be suitably used which does not determine that.

  The hit detection means detects the hit when the value of the amount of change in the rotational speed of the motor is greater than or less than the hit detection threshold, and the motor control means determines the hit according to the value of the motor applied voltage applied to the motor. It is desirable to change the batting detection threshold, and it is desirable to change the batting detection threshold when the number of consecutive battings determined as batting by the batting correctness determination means is a predetermined number or more.

  In the present invention, since the number of operations mistakenly detected as hits is reduced, the estimated torque can be calculated more accurately. For this reason, the motor stops if the set torque is reached during screw tightening. Can be prevented from happening.

  Hereinafter, the present invention will be described based on an embodiment shown in the accompanying drawings. As shown in FIG. 1, this impact tightening tool includes an impact mechanism 1 that applies an impact by a hammer rotated by a motor M to an output shaft, The motor control means 2 that controls the rotation and stop of the motor M, the rotation sensor 3 that generates a predetermined number of pulses per rotation of the motor M, and the rotation that detects the rotation speed based on the pulses of the rotation sensor 3 A speed detection means 4 and a rotation angle detection means 5 for detecting a rotation angle based on the pulse; a striking detection means 6 for detecting a striking operation by the impact mechanism from the amount of change in the rotational speed detected by the rotation speed detection means 4; Torque estimation means 7 for calculating a tightening torque from a hitting interval detected by the hitting detection means 6 and a rotation angle between hitting intervals detected by the rotation angle detecting means 5 In addition to comprising a, and a determining striking accuracy judgment unit 8 whether due actual striking those detected as hitting hitting detector 5. Each of the detection means 4, 5, 6 and the motor control means 2, the torque estimation means 7, and the striking correctness determination means 8 are constituted by a microcomputer.

  The motor control means 2 turns on and off the motor M by operating the trigger switch 9 and determines and outputs the on width of the PWM control according to the operation amount of the trigger switch 9, thereby changing the rotation speed of the motor M. If the tightening torque estimated by the torque estimation means 7 reaches a preset torque value, the motor M is stopped.

  The rotation speed detection means 4 outputs the rotation speed of the motor M by measuring the pulse width output from the rotation sensor 3, and the rotation angle detection means 5 counts the rotation angle by counting the number of pulses. If the reduction ratio from the motor M to the output shaft is B, and the number of pulses output by the rotation sensor 3 with one rotation of the motor is A, the output shaft makes one rotation with an A × B pulse. It will be. Therefore, the output shaft rotation angle between hits can be obtained by counting the number of pulses between hits.

  Next, hit detection by the hit detection means 6 in this example will be described. The hit detection here is performed based on the change amount of the pulse width measured by the rotational speed detection means 4. That is, as shown in FIG. 2, the pulse width measured by the high-pass filter method in which the moving average of the long-term t2 is subtracted from the moving average of the short-term t1 of the speed (pulse width) change is sequentially stored. A result obtained by subtracting the long-term moving average of the pulse width of the predetermined number k from the moving average is obtained, and this is set as a filter processing pulse width change shown in FIG. The difference between the latest filter processing pulse width change Pn and the filter processing pulse width change Pn−m before the predetermined pulse (before the predetermined rotation angle of the output shaft) is the pulse width (rotational speed) change amount shown in FIG. When the pulse width change amount is equal to or greater than a predetermined threshold L2 value, the impact K is detected as the time when the impact K occurred. However, if the threshold width L1 is not detected again unless the pulse width change amount becomes equal to or greater than the predetermined threshold value L1, the speed change other than the impact is erroneously detected as a hit. It reduces the frequency. Further, by setting the threshold value L1 so that the hit detection in the maximum speed state can be performed, the hit detection omission is prevented.

Next, the torque estimating means 7 measures the hitting interval time at each hitting interval (from hitting detection to hitting detection), and performs a torque estimation calculation based on the rotation angle between hits from the rotation angle detecting means 5. Incidentally, the rotation speed = (battering interval time / number of pulses between hits) × speed constant, and the estimated torque = (rotation speed ² / (number of pulses between hits−C / 2)) × torque constant.

  And it is the hitting correctness determination means 8, this also measures the hitting interval time, and if it can be determined that the hitting is based on the hitting interval time or the number of pulses between hits, the estimated torque calculated by the torque estimating means is adopted, If the estimated torque moving average value for a predetermined time exceeds the torque setting value, the motor control means 2 stops the motor, but if it cannot be determined that the hit, the calculated estimated torque is not adopted or the calculation itself is performed. Absent. If not adopted here, all stored estimated torques for a predetermined number of estimated torque moving averages may be cleared to zero. By taking the moving average of the estimated torque, it is possible to reduce the influence of the estimated torque due to erroneous hit detection. FIG. 3 shows a flowchart.

  Here, the correctness determination of the hitting by the hitting correctness determination means 8 is performed as follows. In other words, the hitting interval is determined by the rotational speed of the motor M, the torque characteristics, and the impact mechanism, and the minimum hitting interval and the maximum hitting interval at which a certain impact tightening tool can hit are determined. Therefore, if the hit interval is longer than the above minimum hit interval or shorter than the above maximum hit interval, it is determined that the hit is not hit, and at this time, the estimated torque calculated by the torque estimating means as described above By not adopting, it is determined that the torque is greater than the set torque and is prevented from stopping. Since it is possible to reliably determine whether or not the hit is correct, it is possible to reduce the rate at which it is determined that the set torque has been reached by mistake.

  In addition, since the continuous hitting interval is usually stable, the difference between the previous hitting interval and the current hitting interval is always monitored by the hitting correctness determination means 8, and if the difference is equal to or longer than the predetermined time, hitting is performed. It may be determined that it is not. Since the estimated torque is not calculated when the detected hit is irregular, the accuracy of the estimated torque can be improved.

  However, from the tapping to the start of striking, as shown in FIG. 4, the amount of change in the pulse width usually changes. When the motor is started during tapping, there is a load, so there is a speed fluctuation. Although it occurs and is not in the hit state, it may be detected as hit K. In this case, the striking interval G1 including the tapping period is considerably longer than the striking interval G2 after the actual striking has started. For this reason, in the correctness determination of hitting by the length of the hitting interval, if the difference between the hitting interval G1 and the hitting interval G2 is equal to or longer than a predetermined time, the hitting interval G2 is not determined as hitting, and the estimated torque value due to the first hitting of the hitting interval G2 is not calculated As a result, the determination is delayed by one stroke. The delay for one stroke has no problem in the case of work with a large load, but in the case of a work with a small load such as a small gypsum board work, the determination delay of this one stroke affects the work finish. For this reason, it is preferable that the correctness / incorrectness determination by the hitting correctness determination means 8 is not determined as hitting only when the difference in hitting interval is not less than the predetermined time tk and less than the predetermined time tm in consideration of the tapping time. That is, when the difference between the hitting interval tk and the hitting interval tm is equal to or longer than the predetermined time tm, it is determined that the screw has been tapped, and the estimated torque is calculated at the hitting interval tm. As a result, a delay of one stroke can be prevented, and the accuracy of work finish can be improved.

  In addition, impact tightening tools such as impact drivers allow the hammer to freely rotate relative to the anvil when a force greater than a predetermined value is applied between the hammer and the anvil, and the hammer exceeds a predetermined angle α (a constant determined by the mechanism). After the free rotation, the hammer collides with the anvil. That is, the hammer does not occur unless the hammer rotates by a predetermined angle α. Therefore, when the number of pulses between hits counted by the rotation angle detecting means 5 is equal to or less than the predetermined number of pulses Pα corresponding to the predetermined angle α, it is possible to prevent erroneous detection of hitting by not determining hitting. Further, it is preferable not to determine that the hit is made when the number of pulses between hits is equal to or greater than a predetermined number of pulses. This is because the maximum rotation angle that is rotated by one stroke also has a limitation on the mechanism. In any case, by defining the rotation angle between hits that cannot be assumed by one hit, it is possible to reliably determine whether the hit is correct or not, and it is possible to reduce the ratio of determining that the set torque has been reached by mistake.

  FIG. 5 shows another example. This is a power supply voltage monitoring means 10 added to the above. As described above, the impact tightening tool has a mechanism that does not start hitting unless a predetermined value or more is applied between the hammer and the anvil. Therefore, when the motor control means 2 can adjust the motor rotation speed, that is, the rotation speed of the output shaft by PWM control according to the operation amount of the trigger switch, the battery voltage when the motor M is stopped is If the product of the PWM on-duty (motor applied voltage) for driving the motor is equal to or less than a predetermined value, it is determined that no hit occurs, and the hit correct / incorrect determination means 8 does not determine a hit even if a hit is detected. The estimated torque is not calculated. When the power source is a secondary battery, the voltage fluctuation during driving of the motor increases as the battery capacity decreases. Therefore, the threshold value of the motor applied voltage at which it is determined that no blow occurs may be set corresponding to the voltage. FIG. 6 shows the threshold value LK in this case. In FIG. 6, “a” represents a hit-free area and “b” represents a hit-occurrence area. The threshold value may be set in advance by PWM on-duty corresponding to the battery voltage. It is not determined that the set torque has been reached by mistake at the time of tapping at low speed, and it is possible to reliably determine whether or not the strike is correct even when the power supply voltage varies greatly as in the case of a secondary battery.

  As shown in FIG. 7, when the threshold value LK1 or less is determined to be the region a in which the above-described hit does not occur, a hit occurs between the threshold value LK1 and the threshold value LK2, but since the applied voltage is low, the hit is greater than a predetermined hit interval T1. Alternatively, it may be determined that no blow occurs. The correctness / incorrectness of the hit can be determined more accurately.

  Furthermore, it frequently occurs that the hammer rides on the anvil when the motor M is stopped. However, when the motor M is driven from this state, a hammer is generated when the hammer is detached from the anvil. If this is detected as an impact for tightening, if it is in the process of tapping, it may stop in the middle of tapping. However, since the hitting interval at this time does not occur during tapping, there is a point in time when the previous hitting interval <the current hitting interval occurs, and the normal hitting is gradually shortened and stabilized. Can be distinguished. For this reason, if the previous hit interval <current hit interval, and the current hit interval-previous hit interval> predetermined time, the hammer is removed from the anvil as shown in FIG. Only the striking of the actual striking section tc excluding the section ta and the tapping section tb can be used to calculate the estimated torque, and it is determined that the set torque has been reached by mistake at the start of tapping. Can be prevented.

  Since the hit that occurs when the hammer is removed from the anvil is several hits, the determination may be limited by the number of hits that have occurred continuously.

  Further, the larger the motor applied voltage (the higher the rotation speed), the smaller the pulse width variation at the time of impact as shown on the right side of FIG. 9, and the smaller the motor applied voltage, the smaller the pulse variation at the time of impact on the left side of FIG. As shown in the figure. And, it is easy to detect that there is a strike despite not being hit, when it is easily affected by the fluctuation of the load, and when the pulse width change amount becomes large, that is, when the motor applied voltage is small. For this reason, by changing the impact detection threshold value L as shown in FIG. 10 according to the motor applied voltage value, it is possible to eliminate the influence of small load fluctuations during tapping when the motor applied voltage is small. It is also possible to detect an impact when the applied voltage is large.

  When the impact occurs stably, the load gradually increases, so that the pulse width change amount gradually changes. However, in the work of fastening while cutting screws on the iron plate, the load becomes small (the pulse width change amount is small) when the threading by striking is finished. In order to deal with such work, as shown in FIG. 11, when the number of times that the batting correctness / incorrection judging means 8 has judged the hitting is equal to or more than the predetermined number of times tm, the hitting detecting means 6 sets the hitting detection threshold L to It may be changed. It is possible to eliminate a hit detection omission.

  Further, the estimated torque at the time of screw tightening usually has a form in which the estimated torque rises smoothly as shown in FIG. 14, and the estimated torque rises suddenly when the screw head starts to hit the mating member. However, if it is erroneously determined that there has been a blow during tapping, the result of the calculated estimated torque will not be smooth, and the difference between the current estimated torque and the previous estimated torque may increase. Therefore, when the difference between the estimated torque estimated this time and the estimated torque estimated last time is greater than or equal to a predetermined value, it is determined that the torque estimation is abnormal, and it is desirable not to employ the calculated estimated torque.

It is a block diagram of an example of an embodiment of the invention. It is explanatory drawing about the hit detection by the hit detection means same as the above. (a) (b) is a flowchart same as the above. It is a time chart of an example of operation | movement same as the above. It is a block circuit diagram of the other example same as the above. It is explanatory drawing same as the above. It is explanatory drawing of the other example same as the above. It is a time chart of an example of operation of another example. It is explanatory drawing of another example. It is explanatory drawing of another example. It is a time chart which shows operation | movement of another example. It is a time chart of an example of a torque estimated value change. It is explanatory drawing about the basic operation | movement of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Impact mechanism 2 Motor control means 3 Rotation sensor 4 Rotational speed detection means 5 Rotation angle detection means 6 Stroke detection means 7 Torque estimation means 8 Stroke correct / incorrect determination means M Motor

Claims (8)

  An impact mechanism for applying an impact to the output shaft by a hammer driven to rotate by a motor; motor control means for controlling rotation and stop of the motor; rotation angle detection means for detecting the rotation angle of the motor; A rotational speed detecting means for detecting a rotational speed; a striking detecting means for detecting a striking operation by the impact mechanism from the amount of change in the rotational speed detected by the rotational speed detecting means; a striking interval detected by the striking detection means; Torque estimation means for calculating a tightening torque from a rotation angle detected by the motor rotation angle detection means, and when the estimated torque value estimated by the torque estimation means reaches a predetermined value, In the impact tightening tool in which the motor control means stops the motor, the predetermined condition is satisfied among the hits detected by the hit detection means. Impact fastening tool, characterized in that it comprises a blow correctness determination means not to perform the torque estimation calculation of a torque estimating means based on not the hit.   2. The hit correct / error determination means is characterized in that, of the hits detected by the hit detection means, hits when the hit interval is not less than a predetermined time and / or not more than a predetermined time are not determined as hits. Impact tightening tool.   The hit correct / error determining means is characterized in that, among the hits detected by the hit detecting means, the hit when the difference between the hit interval detected this time and the hit interval detected last time is not less than a predetermined time is not determined as hit. The impact tightening tool according to claim 1.   The batting correctness / error determination means does not determine that the batting is detected when the difference between the hit interval detected this time and the hit interval detected last time is not less than a predetermined time and not more than a predetermined time among the hits detected by the hit detecting means. The impact fastening tool according to claim 1, wherein the impact fastening tool is provided.   The striking correct / incorrect determination means does not determine that the striking when the rotation angle of the motor during the striking interval is equal to or greater than the predetermined angle and / or equal to or smaller than the other predetermined angle among the hits detected by the hit detecting means. The impact tightening tool according to claim 1.   6. The hit correct / error determining means does not determine that the hit detected when the motor applied voltage applied to the motor by the motor control means is equal to or less than a predetermined applied voltage value is a hit. The impact tightening tool according to item 1.   The hit detection means detects the hit when the value of the change in the rotational speed of the motor is greater than or less than the hit detection threshold, and the hit detection is performed according to the value of the motor applied voltage applied to the motor by the motor control means. The impact tightening tool according to any one of claims 1 to 6, wherein the threshold value is changed. The hit detection means detects the hit when the value of the amount of change in the rotation speed of the motor is greater than or less than the hit detection threshold, and the number of consecutive hits determined as hit by the hit correct / error determination means exceeds a predetermined number The impact tightening tool according to any one of claims 1 to 7, wherein the impact detection threshold value is sometimes changed.

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