Screw tightening device

Abstract

To provide a screw fastening device which promptly interrupts screw fastening work when abnormality is determined.SOLUTION: A screw fastening device 1 includes: a bit 2 having an engaging portion 2a which engages with a fastening component S; a motor M provided with an output shaft Ma for rotationally driving the bit 2; an angle detector AS for detecting a rotation angle θ of the bit 2; a torque detector TS for detecting torque applied to the bit 2; and controlling means 30 for controlling rotation of the motor M on the basis of the detected torque T emitted from the torque detector TS. The controlling means 30 is equipped with: an intake part 33 for taking-in data emitted from the angle detector AS and the torque detector TS; and an abnormality determining unit 35 for determining screw fastening abnormality on the basis of a peak A1 (B1) when the detected torque T changed from increasing to decreasing and a bottom point A2 (B2) when it decreased from the peak A1 (B1) and changed to increase again.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a screw tightening device that detects a screw tightening abnormality. [Background technology]

[0002] As shown in Patent Document 1, a conventional screw fastening device includes a motor that rotates, a socket that rotates by receiving the rotational drive of the motor and can engage with a screw fastener to be fastened to a workpiece, a torque detection means that can detect and output the torque applied to the socket, a rotation angle detection means that can detect and output the rotation angle of the socket, and a judgment means that can appropriately judge whether or not there is a screw fastening abnormality based on information output from the torque detection means and the rotation angle detection means. Also, the conventional screw fastening device is configured to store in advance a first reference torque for detecting an abnormality such as a foreign object being caught when the screw fastener is screwed in, and a second reference torque for detecting the completion of fastening of the screw fastener, and to store a torque curve collected at each fastening from the first reference torque to the second reference torque.

[0003] The first reference torque is a value at which a torque increase due to the ingress of foreign matter or the like can be detected before the workpiece and the screw fastener are seated, and is a low value that is not reached during normal screwing until the workpiece and the screw fastener are seated. The torque curve is collected under normal conditions without ingress of foreign matter or the like, and corresponds to the rotation angle of the socket. The determination means is configured to determine whether the torque detected by the torque detection means and the rotation angle detected by the rotation angle detection means are increasing along the torque curve.

[0004] A conventional screw tightening device configured as above has the feature of being able to determine whether or not jamming or the like has occurred after the screw has been tightened, and to notify an operator or the like of the result. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2001-162548 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the conventional screw tightening device judges whether or not a foreign object is caught based on the torque curve from when the first reference torque is reached to when the second reference torque is reached, which is the completion of fastening, and therefore the judgment cannot be made during the screwing process in which the torque curve serving as the judgment criterion is collected. In other words, the conventional screw tightening device judges whether or not a foreign object is caught after the screw tightening is completed, so there is a problem that even if a foreign object is caught during the screwing, it cannot be immediately judged as an abnormality. In this way, a screw part with a foreign object caught in it is forcibly screwed in until the second reference torque is reached, so it is likely to cause seizure between the screw part and the workpiece that is screwed into it. Therefore, the conventional screw tightening device also has the problem of being prone to damaging the screw part and the workpiece. [Means for solving the problem]

[0007] The present invention aims to provide a screw tightening device capable of detecting an abnormality during screwing, the screw tightening device comprising a bit having an engagement portion capable of engaging with a fastening part, a motor having an output shaft capable of rotating the bit, an angle detection portion capable of detecting the rotation angle of the bit, a torque detection portion capable of detecting the torque applied to the bit, and a control means for controlling the rotation of the motor based on the detected torque generated by the torque detection portion, the control means comprising an input portion capable of inputting data generated by the angle detection portion and the torque detection portion, and an abnormality determination portion for determining a screw tightening abnormality based on a peak at which the detected torque changes from an increase to a decrease and a bottom point at which the detected torque decreases from the peak and then increases again. It is preferable that the abnormality determination portion calculates the degree of decrease from the peak to the bottom as a calculated decrease rate, and compares the calculated decrease rate with a preset decrease rate to determine the presence or absence of a screw tightening abnormality. The abnormality determination unit may be configured to count the number of calculations of the calculated decrease rate in one cycle, compare the calculated number of calculations with a preset number of calculations, and determine that a screw tightening abnormality exists if the calculated number of calculations exceeds the set number. Furthermore, the abnormality determination unit may be configured to start calculation of the calculated decrease rate when the detected torque reaches a preset determination start torque. Effect of the Invention

[0008] The screw fastening device according to the present invention recognizes the peak, which is the maximum torque at the time when the torque starts to decrease from the peak and starts to increase again, and the bottom, which is the torque at the time when the torque starts to decrease from the peak and starts to increase again, and judges it as an abnormality if the detected torque has a large torque fluctuation that is excessively wavy due to seizure or the like. In other words, the screw fastening device according to the present invention has the advantage that it is difficult to apply excessive torque to the fastening parts and workpieces because it can interrupt the screw fastening operation before the final tightening torque is reached based on the degree of torque fluctuation during screwing, and has the advantage that it is difficult to apply excessive torque to the fastening parts and workpieces. In addition, the screw fastening device according to the present invention calculates the fluctuation rate of the bottom point relative to the peak as a calculated reduction rate, and judges a screw fastening abnormality based on this calculated reduction rate and a preset set reduction rate, so that the set reduction rate can be set according to, for example, the material of the workpiece. The screw fastening device according to the present invention, which judges an abnormality based on the set reduction rate that is appropriately set and easily changed in this way, can be adapted to various workpieces and screw fastening conditions by changing the setting of the set reduction rate, so that it can judge not only abnormalities due to seizure but also high torque fluctuations due to the inclusion of foreign matter, etc., as abnormalities. Therefore, the screw fastening device according to the present invention can appropriately handle screw fastening with different combinations of materials such as workpieces and fastening parts, and therefore can widen the range in which abnormality can be judged. In addition, by providing a judgment criterion of a set decrease rate, the accuracy of abnormality judgment is improved compared to that of a device that does not provide the criterion. Furthermore, the screw fastening device according to the present invention judges a screw fastening abnormality by comparing the number of calculations of the calculated decrease rate in one cycle with a preset number of times, so that it is possible to improve the accuracy of abnormalities such as foreign matter getting caught and seizing during screwing. In addition, the screw fastening device according to the present invention does not start to judge a screw fastening abnormality until the detected torque during screwing reaches a preset judgment start torque, so that it is possible to avoid making an abnormality judgment in the low torque range at the initial stage of screwing. Therefore, the screw fastening device according to the present invention uses the calculated decrease rate obtained from the peak and bottom as the criterion for abnormality judgment, so that it has the advantage of reducing the frequency of excessive abnormality judgment in a pattern in which a slight torque fluctuation in the low torque range does not need to be regarded as an abnormality. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic explanatory diagram showing an example of a screw fastening device according to the present invention; [Diagram 2] 4A and 4B are examples of torque waveforms displayed on the display unit 34 of the screw fastening device according to the present invention, where (a) shows the torque waveform under abnormal conditions, and (b) shows the torque waveform under normal conditions. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The screw fastening device according to the present invention will be described with reference to Fig. 1 or 2. First, the screw fastening device 1 according to the present invention is configured to be capable of detecting torque fluctuations caused by friction between a fastening part S and a female thread Wa to prevent seizure, and is equipped with a bit 2 having an engagement part 2a that can engage with the fastening part S, a motor M capable of rotating the bit 2, an angle detection unit AS that can output the rotation angle of the bit 2 as a detection angle θ, a torque detection unit TS that detects the load torque applied to the bit 2, and control means 30 that controls the rotation drive of the motor M based on the detected torque T detected by the torque detection unit TS and a preset fastening completion torque TF.

[0011] The fastening part S is made of steel and integrally comprises a male thread Sa that can be screwed into a pilot hole Wa pre-drilled in the workpiece W, and a head Sb that is set to have a larger diameter than the male thread Sa. The head Sb is also formed with a fitting portion Sb1 at its top that can be fitted into the engagement portion 2a of the bit 2.

[0012] One end of the bit 2 forms the engaging portion 2a, and the other end is configured to be connectable to the output shaft Ma of the motor M. In this embodiment, the engaging portion 2a is formed into a protruding cross shape, and is subjected to heat treatment or the like to make it resistant to wear.

[0013] The motor M has a rotatable output shaft Ma, and is connected to a control means 30 described below so as to be able to rotate the output shaft Ma according to a predetermined rotation speed and torque. This allows the motor M to rotate the bit 2 connected thereto, and to transmit the rotation to the fastening part S via the bit 2. The motor M is also attached to a lifting unit 10 which is able to move up and down in the axial direction.

[0014] The lifting unit 10 includes a movable plate 11 that is movable in the axial direction by mounting a motor M thereon, and the movable plate 11 is configured to be capable of moving up and down at a predetermined speed upon receiving a command from a control means 30 described later.

[0015] The angle detection unit AS is configured to detect the rotation angle of the output shaft Ma, and is an encoder in this embodiment. The angle detection unit AS is built in the motor M and configured to transmit a pulse signal corresponding to the rotation angle of the output shaft Ma, and outputs the pulse signal appropriately to the control means 30. Although the angle detection unit AS outputs a pulse signal, it may be configured to calculate the pulse signal as the rotation angle of the output shaft Ma, i.e., bit 2, and transmit it as a detection angle θ to the import unit 33 described later.

[0016] The torque detection unit TS is a torque sensor that is disposed between the output shaft Ma and the bit 2 and is capable of outputting the torque applied to the bit 2 as a detected torque T. Furthermore, this torque detection unit TS is not limited to the torque sensor described above, and may be a unit that calculates the torque applied to the bit 2 based on the load in the rotational direction applied to the output shaft Ma and the load current of the motor M. In this case, the torque detection unit TS may be disposed in the control means 30 to which the motor M is connected.

[0017] As shown in FIG. 1, the control means 30 is composed of a memory unit 31 that pre-stores various setting values ​​related to the operation of the motor M and the lifting unit 10, a control unit 32 that controls the operation of the motor M and the lifting unit 10 based on the information stored in the memory unit 31, an input unit 33 that generates angle-torque data that links the detected angle θ and detected torque T transmitted from the angle detection unit AS and torque detection unit TS connected to the control unit 32, a display unit 34 that displays a torque waveform based on the angle-torque data generated by the input unit 33, and an abnormality judgment unit 35 that judges screw tightening abnormalities based on the stored information in the memory unit 31 and the information from the input unit 33.

[0018] The memory unit 31 stores a tightening completion torque TF, which is the target tightening torque of the fastening part S, a target rotational speed of the output shaft Ma, a target moving speed of the movable plate 11, an operation program that defines a series of operations related to the screw tightening of the motor M and the lifting unit 10, and various judgment values ​​required for judging a screw tightening abnormality.

[0019] The various judgment values ​​required for the aforementioned screw tightening abnormality judgment are a set decrease rate for comparison with a calculated decrease rate described below, a set number of times for comparing the calculated decrease rate in one cycle with the number of calculations performed, and a judgment start torque T1 that serves as a trigger for starting to calculate the calculated decrease rate, and these are stored in advance in memory unit 31.

[0020] The control section 32 transmits appropriate operation commands to the lifting unit 10 and the motor M based on an operation program.

[0021] The input unit 33 converts the pulse signal transmitted from the angle detection unit AS into a detection angle θ of the output shaft Ma, and generates angle-torque data for a series of screw tightening processes from the start of screw tightening to the completion of screw tightening, with the detected torque T received from the torque detection unit TS linked to each converted detection angle θ.

[0022] The display unit 34 is configured to be capable of plotting the detected torque T for each detected angle θ linked by the angle-torque data on a screen with the X-axis as angle and the Y-axis as torque, thereby displaying the torque waveform during screw tightening.

[0023] The abnormality determination unit 35 is connected to the storage unit 31 and the import unit 33, and is configured to be able to import the stored information of the storage unit 31 and the angle-torque data of the import unit 33. The abnormality determination unit 35 also stores in the storage unit 31 as a peak A1 the maximum torque immediately before the detected torque changes from increasing to decreasing as shown in FIG. 2(a) and stores in the storage unit 31 as a bottom point A2 the low torque immediately before the detected torque decreases from the peak A1 and then increases again. The abnormality determination unit 35 further divides the bottom point A2 by the peak A1 to calculate the rate of decrease of the bottom point A2 relative to the peak A1 as a calculated decrease rate, and compares the calculated decrease rate with the set decrease rate previously set in the storage unit 31. At this time, if the calculated reduction rate exceeds the set reduction rate, the abnormality determination unit 35 determines that there is a high possibility of seizure due to large torque fluctuations, determines that a screw tightening abnormality has occurred, and transmits a signal to the control unit 32 to interrupt the screw tightening operation, while displaying a message indicating the occurrence of an abnormality on the display unit 34. In addition, when the torque fluctuates in a wavy manner multiple times as in the peaks (A1, B1, C1, D1) and troughs (A2, B2, C2, D2) in Fig. 2(a), the calculated reduction rate is calculated using the peak A1 (B1, C1, D1) and trough A2 (B2, C2, D2) where the torque decreases from the peak A1 (B1, C1, D1), as in the peak A1 and trough A2, the peak B1 and trough B2, the peak C1 and trough C2, and the peak D1 and trough D2.

[0024] The abnormality determination unit 35 counts the number of calculations of the calculated decrease rate, compares the number of calculations in one cycle of screw tightening with the set number stored in advance in the storage unit 31, and if the number of calculations exceeds the set number, determines that a screw tightening abnormality has occurred, transmits a signal to the control unit 32 to interrupt the screw tightening operation, and displays a message of the occurrence of an abnormality on the display unit 34. Furthermore, the abnormality determination unit 35 compares the detected torque T from the start of screw tightening with the judgment start torque T1 stored in the storage unit 31, and if the detected torque T exceeds the judgment start torque T1, processes to be on standby so that the calculated decrease rate can be calculated. In other words, the abnormality determination unit 35 does not obtain the calculated decrease rate during the tightening process in a low torque range where the detected torque T does not exceed the judgment start torque, and is therefore limited not to determine a screw tightening abnormality in a state where the torque fluctuation is small and the possibility of seizure or the like is low.

[0025] The screw tightening device 1 configured in this manner receives a signal issued by operation of an operator (not shown) or the like and sends an operation command from the control unit 32 to the motor M and the lifting unit 10. As a result, the fastening part S engaged with the bit 2 starts to rotate and descend, so that the tip of the male screw Sa eventually comes into contact with the surface of the workpiece W. The bit 2 continues to rotate and descend, so that the fastening part S is screwed deep into the pilot hole Wa.

[0026] The abnormality determination unit 35 determines whether the detected torque T has reached the determination start torque T1 at the same time as the operation command timing of the motor M and the lifting unit 10. At this time, if the detected torque T has reached the determination start torque T1, it checks the occurrence of a peak A1 and a bottom B1, and counts the number of calculations of the calculated decrease rate calculated based on these repeatedly occurring peaks and bottoms.

[0027] The abnormality judgment unit 35 judges each time the number of calculations described above is exceeded, and if the number of calculations exceeds the set number, sends a signal to the control unit 32 to interrupt the operation of the motor M and the lifting unit 10. If the number of calculations does not exceed the set number, the abnormality judgment unit 35 continues to count the number of calculations.

[0028] The abnormality determination unit 35, upon recognizing both the peak A1 and the valley B1, immediately calculates the calculated decrease rate and determines whether the calculated decrease rate exceeds the set decrease rate. If the calculated decrease rate exceeds the set decrease rate, the abnormality determination unit 35 sends a signal to the control unit 32 to interrupt the operation of the motor M and the lifting unit 10.

[0029] 2(b), the torque waveform has almost no excessive wavy torque fluctuations between the time when the torque waveform reaches the judgment start torque T1 and the time when the torque waveform reaches the make-up completion torque TF. Therefore, the abnormality determination unit 35 determines that no seizure caused by frictional heat between the male thread Sa and the pilot hole Wa has occurred, and completes the screw make-up operation when the make-up completion torque TF is reached.

[0030] In this embodiment, the set reduction rate is set in the range of 10% to 20%, but is not limited to this and is set to a value that does not cause seizure, depending on the materials of the workpiece W and fastening parts S, etc. [Explanation of symbols]

[0031] 1 … Screw tightening device 2 … bits 30 … Control means 31 … Storage section 32 ... Control section 33 ... Intake section 35… Abnormality determination section AS … Angle detection section TS: Torque detector A1 ... Vertex A2 … bottom point

Claims

1. A screw fastening device comprising: a bit having an engagement portion that can engage with a fastening component; a motor having an output shaft that can rotate the bit; an angle detection portion that can detect a rotation angle of the bit; a torque detection portion that can detect a torque applied to the bit; and a control means that controls the rotation of the motor based on the detected torque generated by the torque detection portion, the control means comprises an input unit capable of inputting data generated by the angle detection unit and the torque detection unit, and an abnormality determination unit that determines a screw tightening abnormality based on a peak at which the detected torque changes from an increasing state to a decreasing state and a bottom at which the detected torque decreases from the peak and then changes back to an increasing state, The abnormality determination unit calculates the degree of decrease from the peak to the trough as a calculated decrease rate, and compares this calculated decrease rate with a preset set decrease rate to determine whether or not a screw tightening abnormality exists, and further counts the number of calculations of the calculated decrease rate in one cycle, and compares this calculation number with a preset number of times to determine that a screw tightening abnormality exists if the calculation number exceeds the set number of times.

2. 2. The screw fastening device according to claim 1, wherein the abnormality determination unit starts calculating the calculated decrease rate when the detected torque reaches a preset determination start torque.

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