Screw fixing device

Abstract

The present invention provides a screw-fastening device that can estimate the axial force of a screw generated by screw-fastening. A control unit (31) releases the torque after applying a specified torque generated by a rotating shaft servo motor (10) to the screw in the rotation direction of the fastening screw. Furthermore, the control unit (31) estimates the axial force of the fastened screw based on the change in the rotation position of the rotating shaft servo motor (10) caused by the release of the torque.

Description

Technical Field

[0001] The present invention relates to a screw fastening device for estimating the axial force of a screw generated by screw fastening. Background Art

[0002] As a technique for determining a defective screw fastening, there are the inventions disclosed in the following patent documents 1 and 2. Patent document 1 relates to a device for determining the occurrence and type of defective screw fastening in screw fastening, which determines the occurrence and type of defective screw fastening in screw fastening by a screwdriver based on two or more variables related to a rotating shaft servo motor that generates a rotating motion of a screwdriver and a lifting shaft servo motor that generates a reciprocating motion of the screwdriver in the axial direction.

[0003] Patent document 2 relates to a screw fastening determination device, which is connected to a screw fastening device to determine whether the screw fastening of an object is poor, generates a waveform representing the relationship between the cumulative rotation angle and the current value in the screw fastening device during screw fastening, and determines whether the screw is poorly fastened based on the cumulative rotation angle and the change in the current value in the waveform when the screw fastening is completed.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2020-6452

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-150922 Summary of the invention

[0008] Problems to be solved by the invention

[0009] However, although the above-mentioned Patent Documents 1 and 2 determine whether a screw fastening is insufficient, they do not disclose a technique for determining whether a screw fastening is insufficient by estimating the axial force of the screw.

[0010] An object of an embodiment of the present invention is to realize a screw-fastening device for estimating the axial force of a screw generated by screw-fastening.

[0011] Technical means of solving problems

[0012] In order to solve the above-mentioned problem, the present invention adopts the following structure. One aspect of the present invention comprises a screwdriver head for rotating a screw; a rotary shaft servo motor for driving the screwdriver head for rotation; and a control unit for controlling the rotary shaft servo motor. The control unit applies a prescribed torque generated by the rotary shaft servo motor to the screw in the direction of rotation of the tightening screw, and then performs a step of releasing the torque. Based on the change in the rotation position of the rotary shaft servo motor in the step of releasing the torque, the axial force of the tightened screw is estimated.

[0013] Effects of the Invention

[0014] According to an embodiment of the present invention, the axial force of the screw generated by screw fastening can be estimated. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a diagram showing an outline of the screw-fastening device according to the present embodiment.

[0016] Figure 2 It is a block diagram showing a schematic configuration of a screw fastening device according to the present embodiment.

[0017] Figure 3 This is a diagram that describes the processing flow of the screw-fastening operation of the screw-fastening device according to the present embodiment in a tabular format.

[0018] Figure 4 Yes means Figure 3 Graph showing the rotating shaft torque (R-axis torque) of the rotating shaft servo motor in each step shown.

[0019] Figure 5 It is a diagram schematically showing the axial force generated by tightening the screw.

[0020] Figure 6 This is a graph showing the relationship between the change in the rotational position of the screw and the axial force in a normal state.

[0021] Figure 7 This is a graph showing the relationship between the change in the screw rotation position and the axial force when the screw is turned up and down.

[0022] Figure 8 This is a graph showing the actually measured axial force of the screw and the predicted axial force value calculated using equation (1).

[0023] Fig. 9 It is a depiction Figure 8 Shown is a graph of the predicted axial force values ​​for each sample versus the measured values.

[0024] Fig.10 It is a depiction Figure 8 The graph shown is a graph of the Z-axis position range in step 2 relative to the R-axis position range in step 4 for each sample with top and bottom occurrences of normal and abnormal 2 to abnormal 5.

[0025] Explanation of symbols

[0026] 1: Screw-on device

[0027] 10: Rotary axis servo motor

[0028] 11, 21, 122, 222: Encoder

[0029] 12, 22: Servo drive

[0030] 20: Lifting axis servo motor

[0031] 30: Ball screw

[0032] 31: Control Department

[0033] 40: Screwdriver bit

[0034] 41: Male thread

[0035] 42: Seat surface

[0036] 43: Object to be fastened

[0037] 44: Fasteners

[0038] 121, 221: Inverter

[0039] 123, 223, 311: Ministry of Communications DETAILED DESCRIPTION

[0040] Hereinafter, an embodiment of one aspect of the present invention will be described based on the drawings.

[0041] §1 Application examples

[0042] Figure 1 1 is a diagram showing an overview of the screw-fastening device 1 of the present embodiment. The screw-fastening device 1 includes: a rotating shaft servo motor 10; a first servo driver 12 for controlling the rotation of the rotating shaft servo motor 10; a lifting shaft servo motor 20; a second servo driver 22 for controlling the rotation of the lifting shaft servo motor 20; a ball screw 30; a control unit 31 for sending torque instructions and the like to the first servo driver 12 and the second servo driver 22; and a screwdriver head 40.

[0043] and, Figure 1 Although not described in the specification, the screw-fastening device 1 further includes: a first encoder 11 provided on the rotating axis servo motor 10 ; and a second encoder 21 provided on the lifting axis servo motor 20 .

[0044] The driver bit 40 is attached to the rotating shaft of the rotating shaft servo motor 10, and rotates around the R axis according to the rotation of the rotating shaft servo motor 10. The rotation of the driver bit 40 tightens the screw to be screwed.

[0045] The rotary shaft servo motor 10 and the bit 40 are connected to the lifting shaft servo motor 20 via the ball screw 30. The ball screw 30 converts the rotary motion of the lifting shaft servo motor 20 into a linear motion in the Z-axis direction, so that the rotary shaft servo motor 10 and the bit 40 are lifted and lowered.

[0046] The control unit 31 controls the rotation angle (rotation position), rotation speed and torque of the rotating shaft of the rotating shaft servo motor 10 and the lifting shaft servo motor 20, controls the lifting and lowering of the screwdriver head 40 by the rotation of the lifting shaft servo motor 20, and controls the screwing performed by the screwdriver head 40 by the rotation of the rotating shaft servo motor 10.

[0047] The control unit 31 controls the lifting and lowering of the lifting axis servo motor 20 so that the front end of the screwdriver bit 40 is engaged with the groove of the head of the male thread, and after applying the specified torque generated by the rotating axis servo motor 10 to the screw in the rotation direction of the tightening screw, the step of releasing the torque is started. When the step of releasing the torque starts, the control unit 31 obtains the first rotation angle (rotation position) of the rotating axis of the rotating axis servo motor 10.

[0048] When the control unit 31 has completed releasing the specified torque, the step of releasing the torque ends. When the step of releasing the torque ends, the control unit 31 obtains the second rotation angle (rotation position) of the rotating shaft of the rotating shaft servo motor 10. In addition, the control unit 31 obtains the difference between the first rotation angle and the second rotation angle, and estimates the axial force of the screw based on the change in the rotation angle.

[0049] The control unit 31 estimates the axial force of the tightened screw based on the change in the rotation position of the rotary shaft servo motor. Therefore, it is no longer necessary to measure the actual axial force of the screw, and the quality of the screw tightening can be easily determined.

[0050] §2 Structure Example

[0051] Figure 2 1 is a block diagram showing a schematic structure of the screw-fastening device 1 of the present embodiment. The screw-fastening device 1 includes: a rotating shaft servo motor 10; a first encoder 11, which is provided on the rotating shaft servo motor 10; a first servo driver 12, which controls the driving of the rotating shaft servo motor 10; a lifting shaft servo motor 20; a second encoder 21, which is provided on the lifting shaft servo motor 20; a second servo driver 22, which controls the driving of the lifting shaft servo motor 20; and a control unit 31, which performs overall control of the screw-fastening device 1.

[0052] The first encoder 11 and the second encoder 21 respectively obtain the rotation angles of the rotation axes of the rotation axis servo motor 10 and the lifting axis servo motor 20 , and generate A-phase, B-phase, and Z-phase signals to output as feedback signals.

[0053] The rotating axis servo motor 10 includes a three-phase AC motor, and the rotating axis servo motor 10 is driven according to the three-phase drive signal (U-phase signal, V-phase signal, W-phase signal) output from the first servo driver 12. Similarly, the lifting axis servo motor 20 includes a three-phase AC motor, and the lifting axis servo motor 20 is driven according to the three-phase drive signal (U-phase signal, V-phase signal, W-phase signal) output from the second servo driver 22.

[0054] The first servo driver 12 includes a first inverter unit 121, a third encoder 122, and a first communication unit 123. Moreover, the second servo driver 22 includes a second inverter unit 221, a fourth encoder 222, and a second communication unit 223. In addition, the first inverter unit 121 and the second inverter unit 221 have the same structure and function, the third encoder 122 and the fourth encoder 222 have the same structure and function, and the first communication unit 123 and the second communication unit 223 have the same structure and function. Therefore, only the first servo driver 12 is described in detail, and the detailed description of the second servo driver 22 is not repeated.

[0055] When the first inverter unit 121 receives the command of the rotation angle (rotation position), rotation speed and torque from the control unit 31 via the first communication unit 123, it controls the rotating shaft servo motor 10 according to the command. Specifically, the first inverter unit 121 generates a pulse width modulation (PWM) waveform according to the command from the control unit 31 and the feedback signal from the first encoder 11, and generates an AC current of a required frequency from a DC current. At this time, three drive signals with different phases, namely, a U-phase signal, a V-phase signal and a W-phase signal, are generated and supplied to the rotating shaft servo motor 10.

[0056] Furthermore, the first inverter unit 121 receives a feedback signal from the first encoder 11 provided on the rotating shaft servo motor 10, obtains the actual rotation angle, rotation speed, and driving torque of the rotating shaft servo motor 10, and compares them with the command from the control unit 31, thereby detecting the error between the two. And, the operation of the rotating shaft servo motor 10 is corrected in real time using the error information. The first inverter unit 121 feeds back the actual rotation speed and driving torque of the rotating shaft servo motor 10 to the control unit 31 via the first communication unit 123.

[0057] The third encoder 122 obtains the actual rotation angle of the rotary shaft of the rotary shaft servo motor 10 based on the feedback signal from the first encoder 11 , and feeds back the actual rotation angle to the control unit 31 via the first communication unit 123 .

[0058] The first communication unit 123 communicates with the control unit 31, for example, via a local area network (LAN). The first communication unit 123 receives instructions of the rotation angle (rotation position), rotation speed, and torque from the control unit 31, and outputs them to the first inverter unit 121. Furthermore, when receiving the actual rotation angle of the rotating shaft of the rotating shaft servo motor 10 from the third encoder 122 and the actual rotation speed and driving torque of the rotating shaft servo motor 10 from the first inverter unit 121, these information are sent to the control unit 31.

[0059] The control unit 31 has a third communication unit 311, and communicates with the first servo driver 12 and the second servo driver 22, for example, through a LAN. The control unit 31 sends a command of a rotation angle, a rotation speed, and a torque to the first servo driver 12 and the second servo driver 22 via the third communication unit 311. Furthermore, the control unit 31 receives feedback information related to the actual rotation angle, rotation speed, and driving torque of the rotating shaft of the rotating shaft servo motor 10 and the lifting shaft servo motor 20 from the first servo driver 12 and the second servo driver 22 via the third communication unit 311.

[0060] §3 Action Examples

[0061] (Implementation Method 1)

[0062] Figure 3 This is a diagram that describes the processing flow of the screw-fastening operation of the screw-fastening device 1 of this embodiment in a tabular format. Figure 4 Yes means Figure 3 The diagram of the rotating shaft torque (R-axis torque) of the rotating shaft servo motor 10 in each step is shown. In the diagram, the horizontal axis is time and the vertical axis is R-axis torque. Regarding the time on the horizontal axis, one scale is equivalent to 2ms. Moreover, the R-axis torque on the vertical axis is expressed as a ratio of the rated torque to 100%. Figure 3 as well as Figure 4 , while explaining the operation of the screw-fastening device 1 according to the present embodiment.

[0063] First, the control unit 31 sends a command of the rotation angle, rotation speed, and torque of the lifting axis servo motor 20 to the second servo driver 22. The second servo driver 22 generates a drive waveform according to the command from the control unit 31 and supplies it to the lifting axis servo motor 20 (starting from step 0). At this time, the screwdriver head 40 is at the origin position and descends along the Z axis at a specified moving speed (Vz) according to the drive waveform.

[0064] The position (z) and the moving speed (Vz) of the driver bit 40 can be calculated based on the rotation angle or the rotation speed of the rotating shaft of the lifting axis servo motor 20. The control unit 31 moves the driver bit 40 to a target position.

[0065] When the control unit 31 detects that the Z-axis position (z) of the screwdriver head 40 has reached the target position, it instructs the second servo driver 22 to stop driving the lifting axis servo motor 20 (step 0 ends). Figure 4 As shown, during step 0, the rotary axis servomotor 10 is not driven, so the R-axis torque is kept at zero.

[0066] Next, the control unit 31 sends a command of the rotation speed of the rotary shaft servo motor 10 to the first servo driver 12. The first servo driver 12 generates a drive waveform according to the command from the control unit 31 and supplies it to the rotary shaft servo motor 10. At this time, the screwdriver bit 40 rotates around the R axis at a predetermined rotation speed (Vr) and starts screwing (step 1 (first step) starts).

[0067] Furthermore, the screw moves downward by the rotation of the screw, so the control unit 31 rotates the lifting axis servo motor 20 in synchronization with the movement amount to move the screwdriver head 40 downward along the Z axis. At this time, if the front end of the screwdriver head 40 is not fitted into the groove of the screw head, the screwdriver head 40 is fitted into the groove of the screw head by rotating around the R axis and moving downward.

[0068] like Figure 4 As shown in FIG. 1 , the rotating shaft of the rotating shaft servo motor 10 rotates at a predetermined rotation speed (Vr), so the R-axis torque increases, but overshoot occurs only at the beginning. The control unit 31 determines whether it is in a temporary seated state (the seat surface of the screw contacts the fastened part) based on whether the R-axis torque has reached a threshold torque (for example, 62%), but since the overshoot of the R-axis torque must be excluded, the determination of whether it is in a temporary seated state is not performed for 1000ms from the start of step 1.

[0069] When the screw is temporarily seated, the first servo driver 12 maintains the specified rotation speed (Vr) and the R-axis torque further increases. When the driving torque received from the first servo driver 12 reaches the threshold torque, the control unit 31 shifts to step 2. In this way, the control unit 31 rotates the rotary axis servo motor 10 around the R-axis at a specified rotation speed until the R-axis torque reaches the threshold torque, and moves the screwdriver head 40 downward along the Z-axis direction by rotating the lifting axis servo motor 20 (end of step 1).

[0070] Next, the control unit 31 maintains the first servo driver 12 at a predetermined rotation speed (Vr) to perform the actual tightening of the screws. As a result, the R-axis torque gradually increases. Here, the R-axis torque of about 150% is set as the tightening torque (step 2 (second step) starts).

[0071] Furthermore, since the screw moves downward by being formally tightened, the control unit 31 rotates the lifting axis servo motor 20 in synchronization with the movement amount, so that the screwdriver head 40 moves downward along the Z axis. Figure 4 As shown, the R-axis torque (Tr) of the rotary axis servomotor 10 reaches the tightening torque (end of step 2).

[0072] Next, when the control unit 31 detects that the R-axis torque (Tr) of the rotary axis servo motor 10 has reached the tightening torque, it maintains the torque command to the first servo driver 12 at the tightening torque, thereby maintaining the tightening torque of the screw for tightening. Figure 4 As shown, the tightening torque is maintained for a specified time. During the specified time, the rotation of the screw stops and no further tightening is performed. (Step 3 ends).

[0073] Furthermore, since the screw moves downward by tightening the screw, the control unit 31 rotates the lifting axis servo motor 20 in synchronization with the amount of movement to move the screwdriver bit 40 downward along the Z axis.

[0074] Next, the control unit 31 sends a command to reduce the R-axis torque (Tr) to the first servo driver 12 (starting from step 4). Furthermore, the control unit 31 sets the rotation angle of the rotating shaft of the rotating shaft servo motor 10 at the start of step 4 to the first rotation angle. Furthermore, the control unit 31 sends a command to the first servo driver 12 to reduce the R-axis torque (Tr) of the rotating shaft servo motor 10 to 0. At this time, due to the release of the R-axis torque, the screw rotates slightly in the direction opposite to the tightening direction. The rotation angle of the rotating shaft of the rotating shaft servo motor 10 at this time is set to the second rotation angle (ending of step 4).

[0075] Finally, the control unit 31 sends the second servo driver 22 the command of the rotation angle, speed and torque of the lifting axis servo motor 20. The second servo driver 22 generates a drive waveform according to the command from the control unit 31 and supplies it to the lifting axis servo motor 20 (starting from step 5). At this time, the screwdriver head 40 rises along the Z axis at a predetermined moving speed (Vz).

[0076] Furthermore, the control unit 31 sends a command of the rotation angle, rotation speed, and torque of the rotating axis servo motor 10 to the first servo driver 12. The first servo driver 12 generates a drive waveform according to the command from the control unit 31 and supplies it to the rotating axis servo motor 10. At this time, the screwdriver bit 40 rotates around the R axis at a predetermined rotation speed (Vr). The control unit 31 ends the processing when the rotation angle (R axis position (r)) of the rotating axis of the rotating axis servo motor 10 and the Z axis position (z) of the screwdriver bit 40 return to the origin position (step 5 ends).

[0077] Figure 5 Schematically shows the axial force generated by screw tightening. The male thread 41 is tightened to the female thread of the fastened object 44 by sandwiching the fastened object 43 through the seat surface 42. At this time, an axial force F of the same magnitude as the force for tightening the fastened object 43 through the seat surface 42 of the male thread 41 is generated. That is, the greater the force for tightening through the male thread 41, the greater the axial force F.

[0078] If used Figure 3 As described above, when the rotation angle of the rotating shaft of the rotating shaft servo motor 10 when the tightening of the screw is completed in step 3 is set to the first rotation angle, and the rotation angle when the tightening of the screw is released in step 4 is set to the second rotation angle, the rotation angle of the screw returns to (first rotation angle - second rotation angle). The return of the rotation angle of the screw (rotating shaft of the rotating shaft servo motor 10) is called a change in the rotation position.

[0079] When the axial force F is small, the surface pressure (screw contact surface pressure) of the seat surface 42 decreases, and the rotation resistance decreases. As a result, the change in the rotation position of the screw (rotating shaft of the rotating shaft servo motor 10) increases.

[0080] Furthermore, when the axial force F is large, the surface pressure of the seat surface 42 (screw contact surface pressure) increases, and the rotation resistance increases. As a result, the change in the rotation position of the screw (rotating shaft of the rotating shaft servo motor 10) decreases. The control unit 31 estimates the axial force F according to the change in the rotation position.

[0081] Figure 6 This is a graph showing the relationship between the change in the screw's rotational position and the axial force F under normal conditions. Figure 3 as well as Figure 4 As described above, the tightening torque of the screw is maintained for a predetermined time (step 3), and when the tightening torque is released (step 4), the rotational position changes. Figure 6 The rotation position changes by 3.8°. At this time, the axial force F is about 100 kgf.

[0082] in addition, Figure 6 to Figure 9In the present invention, since the axial force of the screw cannot be measured in the usual process, the screw is fastened with a force sensor sandwiched between the fastened object 43 and the fastened object 44, and the axial force of the screw is measured by experiment.

[0083] Figure 7 This is a graph showing the relationship between the change in the rotational position of the screw and the axial force F during top-bottom. The so-called top-bottom refers to the state where the front end of the male thread 41 contacts the bottom of the female thread, which is a state where normal screwing cannot be performed. When top-bottom occurs, the front end of the male thread 41 or the bottom of the female thread will break during the formal tightening, making it impossible to perform normal screwing. As a result, compared with normal screwing, the axial force F decreases and the change in the rotational position of the screw increases.

[0084] Figure 7 In the example, the rotation position changes by 5.0°. At this time, the axial force F is about 10 kgf. It can be seen that there is a correlation between the change in the rotation position of the screw and the axial force F.

[0085] As described above, according to the screw-fastening device of this embodiment, when the axial force F is small, the surface pressure of the seat surface 42 becomes small, and the rotational resistance becomes small. As a result, the change of the rotational position of the screw becomes larger. Moreover, when the axial force F is large, the surface pressure of the seat surface 42 becomes large, and the rotational resistance becomes large. As a result, the change of the rotational position of the screw becomes smaller. The control unit 31 can infer the axial force F based on the change of the rotational position.

[0086] (Implementation Method 2)

[0087] In implementation mode 1, the axial force of the screw is estimated only within the R-axis position range, but further investigation is conducted to determine whether there are no variables that can improve the estimation accuracy of the axial force. As a result of experiments conducted by the applicant, the following formula is proposed as a model for estimating the axial force F. Here, y is set as the estimated axial force, x1 is set as the standard deviation of the Z-axis torque in step 1, x2 is set as the average of the R-axis speed in step 2, and x3 is set as the variation of the R-axis position in step 4 (the maximum value of the R-axis position - the minimum value of the R-axis position (R-axis position range)). Moreover, a, b, c, and d are constants obtained through experiments.

[0088] y=ax1+bx2+cx3+d…(1)

[0089] In step 1, if the screw is not properly seated and idles, the R-axis torque will remain below the threshold torque and a fixed torque will be generated for a long time. At this time, the standard deviation x1 of the Z-axis torque decreases. Therefore, the variable x1 can be used to determine whether the temporary seating of the screw has been successful (whether an axial force has been generated).

[0090] In step 2, if the time until the R-axis torque reaches the target value is long due to poor tightening of the screw, or if the target value is not reached, the R-axis speed will be approximately 0 for a long time, and the average x2 of the R-axis speed will decrease. Therefore, the variable x2 can be used to determine whether the formal tightening of the screw can be carried out normally (whether the axial force is generated).

[0091] In step 4, when the R-axis torque is released, a force is generated to rotate in the direction of loosening the screw. Depending on the tightening state of the screw, the amount of screw reversal varies, and the tighter the tightening, the smaller the amount of rotation. That is, the R-axis position range x3 becomes smaller. Therefore, the variable x3 can be used to determine whether it is firmly tightened (whether axial force is generated) after formal tightening. As a variable with a high correlation (replaceable) with the variable x3, the R-axis speed range of step 4 can be listed.

[0092] Figure 8 This is a graph showing the actual measured axial force of the screw and the predicted axial force calculated using formula (1). In the graph, the horizontal axis is set to the test (sample) number, and the vertical axis is set to the axial force (kgf). Samples up to about 300 of the test number are screwed in a normal state, and samples thereafter are screwed in an abnormal (abnormal) state. In addition, the measured values ​​of the axial force are represented by points, and the predicted values ​​of the axial force are represented by solid lines. The measured values ​​of the axial force are recorded as points of different shapes in normal and abnormal 1 to abnormal 6.

[0093] Abnormality 1 is a sample with a defective thread. Abnormalities 2 to 5 are samples with top and bottom, and are classified into four types according to the degree of top and bottom. Abnormality 2 is the sample with the lightest top and bottom degree, abnormality 5 is the sample with the heaviest top and bottom degree, and abnormalities 3 and 4 are samples with intermediate degrees. Abnormality 6 is a sample when a foreign object is caught between the seat surface 42 of the male thread 41 and the fastened object 43.

[0094] like Figure 8 As shown, in normal and abnormal 1 to abnormal 5, the actual measured axial force of the screw is roughly consistent with the predicted axial force value. However, in abnormal 6 (foreign matter is caught), the difference between the actual measured axial force of the screw and the predicted axial force value is large, which shows that the prediction accuracy is not very good. For samples where the foreign matter is caught, as long as other methods are used to detect and eliminate it, and only the axial force estimation is used for normal and abnormal 1 to abnormal 5 samples, the axial force can be estimated with higher accuracy.

[0095] Fig. 9 It is a depiction Figure 8The graph of the predicted axial force values ​​of each sample relative to the measured values ​​is shown in FIG. In the graph, the horizontal axis is the predicted axial force value (kgf), the vertical axis is the measured axial force value (kgf), and the points of each sample correspond to Figure 8 The points of each sample are shown. Fig. 9 In, it has been excluded Figure 8 A sample with abnormality 6 (foreign matter inclusion) is shown.

[0096] like Fig. 9 As shown, the predicted axial force values ​​are roughly consistent with the measured axial force values ​​in each of the normal and abnormal 1 to abnormal 5 samples. Moreover, the predicted axial force values ​​can be roughly determined in which state the vehicle is in: normal or abnormal 1 to abnormal 5.

[0097] As described above, the control unit 31 estimates the axial force of the screw using the formula (1), and therefore can estimate the axial force of the screw more accurately than estimating the axial force of the screw based only on the change in the rotational position of the screw.

[0098] (Implementation method 3)

[0099] Variables that are highly correlated (replaceable) with the variable x1 include the average Z-axis position in step 1 (correlation coefficient with variable x1 is 0.97), the time in step 1 (correlation coefficient with variable x1 is 0.99), the average R-axis position in step 1 (correlation coefficient with variable x1 is 0.99), the standard deviation of the R-axis position (correlation coefficient with variable x1 is 0.99), the average R-axis speed (correlation coefficient with variable x1 is 0.97), and the average R-axis speed (correlation coefficient with variable x1 is -0.96). By replacing x1 with any of the above variables or applying them together with x1, it is expected that the estimation accuracy will be further improved.

[0100] (Implementation 4)

[0101] Variables with high correlation (replaceable) with the variable x2 include the time of step 2 (correlation coefficient with variable x2 is -0.77), the standard deviation of the R-axis position in step 2 (correlation coefficient with variable x2 is -0.75), the standard deviation of the R-axis speed (correlation coefficient with variable x2 is 0.94), the average of the R-axis torque (correlation coefficient with variable x2 is 0.84), the Z-axis position range (maximum value of the Z-axis position - minimum value of the Z-axis position) (correlation coefficient with variable x2 is -0.74), etc. By replacing x2 with any of the above variables or applying them together with x2, it is expected that the estimation accuracy will be further improved.

[0102] (Implementation 5)

[0103] Fig.10It is a depiction Figure 8 The graph shown is a graph of the Z-axis position range in step 2 relative to the R-axis position range in step 4 for each sample with top and bottom occurrences of normal and abnormal 2 to abnormal 5. Fig.10 It is shown that, by utilizing the fact that the axial force of the screw can be estimated using the R-axis position range as described above, the quality determination is performed by two-dimensionally plotting the R-axis position range and other variables, and the determination accuracy is good.

[0104] In the graph, the horizontal axis is set to the Z-axis position range (mm) in step 2, and the vertical axis is set to the R-axis position range (°) in step 4. The points of each sample correspond to Figure 8 The points of each sample where the top and bottom occurred are shown for normal and abnormal 2 to abnormal 5.

[0105] For each sample, the Z-axis position range in step 2 and the R-axis position range in step 4 are applied with isolation forest, which is a method of machine learning, to calculate a score. Fig.10 In the figure, the contour lines represent the scores, and it can be seen that the scores of the samples in the normal state are concentrated below 0.55. In this way, the samples with scores below the specified value can be judged as the samples that have been screwed normally.

[0106] As described above, the control unit 31 applies the isolation forest to each sample in the Z-axis position range in step 2 and the R-axis position range in step 4 to estimate the axial force of the screw, so that the quality of the screw tightening can be easily determined based on the numerical value.

[0107] §4 Variations

[0108] The control block (especially the control unit 31 ) of the screw fastening device 1 may be realized by a logic circuit (hardware) formed on an integrated circuit (IC (Integrated Circuit) chip) or the like, or may be realized by software.

[0109] In the latter case, the screw-fastening device 1 includes a computer that executes the commands of the software, i.e., the program, that realizes each function. The computer includes, for example, one or more processors (processors), and includes a computer-readable recording medium that stores the program. In addition, in the computer, the program is read and executed from the recording medium by the processor, thereby achieving the purpose of the present invention. As the processor, for example, a central processing unit (CPU) can be used. As the recording medium, "non-temporary tangible media" can be used, for example, in addition to read-only memory (ROM), tape, disk, card, semiconductor memory, programmable logic circuit, etc. can also be used. Moreover, a random access memory (RAM) that expands the program can also be included. Moreover, the program can also be provided to the computer via any transmission medium (communication network or broadcast wave, etc.) that can transmit this program. In addition, one embodiment of the present invention can also be implemented in the form of a data signal embedded in a carrier that materializes the program through electronic transmission.

[0110] (Summarize)

[0111] In order to solve the above-mentioned problem, the present invention adopts the following structure. One aspect of the present invention comprises a screwdriver head for rotating a screw; a rotary shaft servo motor for driving the screwdriver head for rotation; and a control unit for controlling the rotary shaft servo motor. The control unit applies a prescribed torque generated by the rotary shaft servo motor to the screw in the direction of rotation of the tightening screw, and then performs a step of releasing the torque. Based on the change in the rotation position of the rotary shaft servo motor in the step of releasing the torque, the axial force of the tightened screw is estimated.

[0112] According to the above configuration, the axial force of the tightened screw is estimated based on the change in the rotational position of the rotary shaft servo motor. Therefore, it is no longer necessary to measure the actual axial force of the screw, and the quality of the screw tightening can be easily determined.

[0113] The screw-fastening device of one aspect further includes: a lifting axis servo motor, which is controlled by a control unit and moves the screwdriver head in the axial direction. The control unit executes: a first step for screwing the screw into the screw hole, setting the rotating axis servo motor to a specified rotation speed, and moving the screwdriver head by the lifting axis servo motor until the torque generated by the rotating axis servo motor reaches a threshold torque; then executes: a second step for formally tightening the screw, increasing the torque generated by the rotating axis servo motor until it reaches the specified torque.

[0114] According to the above structure, the screw can be seated correctly through the first step, and the screw can be properly tightened through the second step.

[0115] In the screw-fastening device of the first aspect, the control unit reflects the unevenness of the torque of the lifting axis servo motor in the first step to estimate the axial force.

[0116] According to the above configuration, the axial force can be estimated taking into account whether the screw has been successfully seated, so that the axial force can be estimated more accurately than estimating the axial force based only on the change in the rotation position of the rotary shaft servo motor.

[0117] In the screw-fastening device on the one hand, the control unit reflects any one of the average position of the lifting axis servo motor relative to the screwdriver head in the first step, the time of the first step, the average rotation position of the rotating axis servo motor, the standard deviation of the rotation position of the rotating axis servo motor, the average rotation speed of the rotating axis servo motor, and the standard deviation of the rotation speed of the rotating axis servo motor to infer the axial force.

[0118] According to the above configuration, the axial force of the screw can be estimated using any variable. Therefore, the axial force of the screw can be estimated using a variable that can be more easily obtained than the torque variation of the lifting axis servo motor.

[0119] In the screw fastening device of the first aspect, the control unit reflects an average value of the rotation speed of the rotating shaft servo motor in the second step to estimate the axial force.

[0120] According to the above configuration, the axial force can be estimated by taking into account whether the screw is properly tightened. Therefore, the axial force can be estimated more accurately than estimating the axial force based only on the change in the rotation position of the rotary shaft servo motor.

[0121] In the screw-fastening device of one aspect, the control unit reflects any one of the time of the second step, the standard deviation of the rotation position of the rotating axis servo motor in the second step, the standard deviation of the rotation speed of the rotating axis servo motor, the average of the torque of the rotating axis servo motor, and the range of the position of the lifting axis servo motor relative to the screwdriver head to infer the axial force.

[0122] According to the above configuration, the axial force of the screw can be estimated using any variable. Therefore, the axial force of the screw can be estimated using a variable that is easier to obtain than the average value of the rotation speed of the rotary shaft servo motor.

[0123] In the screw fastening device of the first aspect, the control unit determines whether the screw is fastened properly based on the change in the position of the screwdriver bit of the lifting axis servo motor and the estimated axial force in the second step.

[0124] According to the above configuration, it is possible to perform a multi-faceted determination of whether screw tightening is good or not.

[0125] In the screw fastening device of one aspect, the control unit applies the isolation forest to the change in the position of the screwdriver bit by the lifting shaft servo motor and the estimated axial force in the second step, and determines whether the screw is fastened well based on the score.

[0126] According to the above configuration, since the isolation forest is applied to determine the quality of screw tightening, the quality of screw tightening can be objectively determined by numerical values.

[0127] In the screw fastening device according to the first aspect, the control unit executes a step of maintaining the predetermined torque for a predetermined time before the step of releasing the torque.

[0128] According to the above configuration, the screw can be tightened by maintaining the predetermined torque for a predetermined time.

[0129] The present invention is not limited to the above-described embodiments, and various changes can be made within the scope of the claims. Embodiments obtained by appropriately combining the technical components disclosed in different embodiments are also included in the technical scope of the present invention. In each embodiment, step 3 is not necessarily required and can be omitted.

Claims

1. A screw-fastening device, comprising: The screwdriver bit turns the screw; A rotating shaft servo motor drives the screwdriver head to rotate; as well as A control unit controls the rotating shaft servo motor, The control unit applies a predetermined torque generated by the rotary shaft servo motor to the screw in a rotation direction for tightening the screw, and then releases the torque. The axial force of the tightened screw is estimated based on the change in the rotational position of the rotary shaft servo motor in the step of releasing the torque.

2. The screw-fastening device according to claim 1, further comprising: The lifting axis servo motor is controlled by the control unit and moves the screwdriver head in the axial direction. The control unit executes: a first step for screwing the screw into the screw hole, setting the rotating axis servo motor to a predetermined rotation speed, and moving the screwdriver head by the lifting axis servo motor until the torque generated by the rotating axis servo motor reaches a threshold torque; Next, a second step for performing the final tightening of the screw is performed, in which the torque generated by the rotating shaft servo motor is increased until it reaches the predetermined torque.

3. The screw-fastening device according to claim 2, wherein The control unit reflects any one of the average value of the position of the screwdriver head by the lifting axis servo motor in the first step, the time of the first step, the average value of the rotation position of the rotating axis servo motor, the standard deviation of the rotation position of the rotating axis servo motor, the average value of the rotation speed of the rotating axis servo motor, and the standard deviation of the rotation speed of the rotating axis servo motor to infer the axial force.

4. The screw-fastening device according to any one of claims 2 to 3, wherein The control unit estimates the axial force by reflecting an average value of the rotation speed of the rotary shaft servomotor in the second step.

5. The screw-fastening device according to any one of claims 2 to 3, wherein The control unit reflects any one of the time of the second step, the standard deviation of the rotation position of the rotating axis servo motor in the second step, the standard deviation of the rotation speed of the rotating axis servo motor, the average value of the torque of the rotating axis servo motor, and the range of the position of the lifting axis servo motor relative to the screwdriver head to infer the axial force.

6. The screw-fastening device according to any one of claims 2 to 3, wherein The control unit determines whether the screw is fastened well or not based on the change in the position of the screwdriver bit caused by the lifting axis servo motor in the second step and the estimated axial force.

7. The screw-fastening device according to claim 6, wherein The control unit applies isolation forest to the change in the position of the screwdriver bit caused by the lifting axis servo motor and the estimated axial force in the second step, and determines whether the screw is tightened well based on the score.

8. The screw-fastening device according to any one of claims 1 to 3, wherein Before the step of releasing the torque, the control unit A step of maintaining the prescribed torque for a prescribed time is performed.

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