Screw tightening device

Abstract

To provide a screw tightening device that can accurately detect the position where the tips of a male screw and a female screw engage when tightening a male screw into a female screw. [Solution] The screw tightening device 100 comprises a bit 1, a motor 2, a lifting mechanism 3, a first detector 4, a second detector 5, and a control unit. When the motor 2 is rotated in the opposite direction to the screw tightening direction with the male screw 200 in contact with the female screw 201, the control unit determines the lowest point of the lifting mechanism 3 as the meshing position between the male screw 200 and the female screw 201 from the continuous change in position or acceleration of the lifting mechanism 3 detected by the second detector 5. The control unit calculates the screw seating position by adding the amount of rotation of the motor 2 corresponding to the effective length of the male screw 200 to the rotation position of the motor 2 detected by the first detector 4 at the meshing position between the male screw 200 and the female screw 201.

Description

Technical Field

[0001] The present disclosure relates to a screwing device used for screwing a male screw into a female screw.

Background Art

[0002] Conventionally, there is known a screwing device that rotates a male screw by a motor to screw the male screw into a female screw. In the screwing device, when the male screw is fully tightened, if the rotation speed of the motor is high, the motor may overshoot and the male screw may be subjected to more torque than expected. In order to suppress the torque, it is necessary to slow down the rotation speed of the motor when the male screw is fully tightened, but if the rotation speed of the motor is slow, the time required for screwing will become long.

[0003] For example, in the technique disclosed in Patent Document 1, the total screwing amount of the male screw is divided into three sections of 1 / 4, 2 / 4, and 1 / 4. The first 1 / 4 is a weak torque, the next 2 / 4 is a strong torque, and the last 1 / 4 is a weak torque to prevent the motor from being overloaded. In Patent Document 1, when tightening the male screw into the female screw, after the tip of the male screw is brought into contact with the tip of the female screw, the motor is rotated in a direction opposite to the direction of tightening the male screw into the female screw, and the male screw is raised along the helix of the female screw. The position of the male screw is measured every sampling period. The rise and fall of the male screw are detected by the difference between the latest measured value and the value measured one time before. Then, when the tip of the male screw passes through the cut at the upper end of the helix of the female screw, the male screw descends, and from the state where the male screw and the female screw are engaged, the motor is rotated forward by torque control to tighten the male screw into the female screw.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, as in the technology disclosed in Patent Document 1, simply rotating the motor in the opposite direction to the direction in which the male screw is tightened into the female screw, and determining the downward movement of the male screw based on the difference between the most recently measured value and the value measured one measurement earlier, does not provide enough data to determine the position of the male screw. For example, vibrations in the direction of the screw axis may prevent accurate detection of the position where the tips of the male screw and the female screw engage. If the position where the tips of the male screw and the female screw engage cannot be accurately detected, the torque switching may be out of sync with the intended timing, making it impossible to accurately control the motor's torque. This may result in applying more torque than intended to the male screw or increasing the time required to tighten the screw.

[0006] This disclosure has been made in view of the above, and aims to provide a screw tightening device that can accurately detect the position where the tip of a male screw and the tip of a female screw engage when tightening a male screw into a female screw. [Means for solving the problem]

[0007] To solve the above-mentioned problems and achieve the objective, the screw tightening device according to the present disclosure is a screw tightening device used for tightening a male screw into a female screw, and comprises a bit for tightening the male screw, a motor for rotating the bit, a lifting mechanism for raising and lowering the motor, a first detector for detecting the rotational position of the motor, a second detector for detecting the position or acceleration of the lifting mechanism, and a control unit for controlling the motor and the lifting mechanism. The control unit, with the male screw held in the bit in contact with the female screw, rotates the motor in the opposite direction to the screw tightening direction. Based on the continuous change in position or acceleration of the lifting mechanism detected by the second detector, the control unit determines the lowest point of the lifting mechanism as the engagement position between the male and female screws. At the engagement position between the male and female screws, the control unit calculates the screw seating position by adding the amount of motor rotation corresponding to the effective length of the male screw to the motor rotation position detected by the first detector. Based on the value detected by the first detector, the control unit increases the motor rotation speed to high until just before the screw seating position to temporarily tighten the male screw into the female screw, and then controls the motor rotation speed to low to fully tighten the male screw into the female screw. [Effects of the Invention]

[0008] The screw tightening device according to this disclosure has the effect of being able to accurately detect the position where the tip of the male screw and the tip of the female screw engage when tightening a male screw into a female screw. [Brief explanation of the drawing]

[0009] [Figure 1] Perspective view showing a screw tightening device according to an embodiment. [Figure 2] Block diagram of a screw tightening device according to an embodiment. [Figure 3] This diagram illustrates the first step in the procedure for aligning the tip of a male screw with the tip of a female screw using the screw tightening device according to this embodiment. [Figure 4] This diagram illustrates the second step in the procedure for aligning the tip of a male screw with the tip of a female screw using the screw tightening device according to the embodiment. [Figure 5]This diagram illustrates the third step in the procedure for aligning the tip of a male screw with the tip of a female screw using the screw tightening device according to the embodiment. [Figure 6] In the screw tightening device according to the embodiment, this graph shows the waveform of the changes in the detected value obtained by the second detector when the lifting mechanism is driven. [Figure 7] Part VII shown in Figure 6 is a graph showing the moving average line. [Figure 8] A flowchart illustrating the screw tightening process of a screw tightening device according to an embodiment. [Figure 9] This diagram illustrates the periodic interrupt processing performed during the screw tightening process of the screw tightening device according to the embodiment. [Figure 10] A flowchart showing the periodic interrupt process executed in the periodic interrupt processing of the screw tightening device according to the embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, a screw tightening device according to an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0011] Embodiment. Figure 1 is a perspective view showing a screw tightening device according to an embodiment. Figure 2 is a block diagram of the screw tightening device according to an embodiment. As shown in Figure 1, the screw tightening device 100 according to the embodiment is used to tighten a male screw 200 into a female screw 201. As shown in Figures 1 and 2, the screw tightening device 100 comprises a bit 1, a motor 2, a lifting mechanism 3, a first detector 4, a second detector 5, and a control unit 6. The screw tightening device 100 transmits the torque generated by the rotation of the motor 2 to the male screw 200 through the bit 1.

[0012] Bit 1 is attached to motor 2 and rotates when driven by motor 2, thereby rotating the male screw 200. The tip of bit 1 is shaped like, for example, a Phillips screwdriver, a flathead screwdriver, or a hexagonal bolt, and is fitted into a groove formed in the screw head of male screw 200. Motor 2 rotates in the direction that tightens male screw 200 into female screw 201, and in the opposite direction. In the following description, the direction that tightens male screw 200 into female screw 201 may be referred to as the screw tightening direction, and the opposite direction may be referred to as the reverse direction. Motor 2 moves vertically by the lifting mechanism 3. As motor 2 moves vertically by the lifting mechanism 3, bit 1 attached to motor 2 also moves vertically with motor 2. That is, as motor 2 moves downward by the lifting mechanism 3, bit 1 moves downward, pressing male screw 200 against female screw 201. The first detector 4 detects the rotational position of motor 2. The second detector 5 detects the vertical position of the lifting mechanism 3. The first detector 4 is, for example, an encoder. The second detector 5 is, for example, an encoder or a linear scale.

[0013] The control unit 6 controls the motor 2 and the lifting mechanism 3. The control unit 6 is implemented by a processing circuit. The processing circuit may be a circuit comprising a memory for storing a program and a processor for executing the program stored in the memory, or it may be a dedicated circuit.

[0014] Next, the operation of fastening the male screw 200 into the female screw 201 on the mating side using the screw fastening device 100 will be explained. Figure 3 is an explanatory diagram showing the first step in the procedure of aligning the tip of the male screw with the tip of the female screw using the screw fastening device according to the embodiment. Figure 4 is an explanatory diagram showing the second step in the procedure of aligning the tip of the male screw with the tip of the female screw using the screw fastening device according to the embodiment. Figure 5 is an explanatory diagram showing the third step in the procedure of aligning the tip of the male screw with the tip of the female screw using the screw fastening device according to the embodiment. The arrows shown in Figures 4 and 5 indicate the direction of movement of the male screw 200.

[0015] As shown in FIG. 1, with a male screw 200 held at the tip of the bit 1, the elevator mechanism 3 is lowered to lower the bit 1 together with the motor 2. When the detection value of the second detector 5 no longer changes, that is, when the movement of the elevator mechanism 3 stops, as shown in FIG. 3, the control unit 6 determines that the tip of the male screw 200 has contacted almost directly above the tip of the female screw 201. When the control unit 6 determines that the male screw 200 has contacted the female screw 201, as shown in FIG. 4, while pressing the male screw 200 against the female screw 201 by the elevator mechanism 3, the motor 2 is rotated in a direction opposite to the direction of tightening the male screw 200 against the female screw 201. Then, as shown in FIG. 5, at a position where the tip of the helix of the female screw 201 coincides with the tip of the helix of the male screw 200, the male screw 200 descends by one pitch. The control unit 6 continuously acquires the detection value detected by the first detector 4 and stores the detection value when rotating the motor 2 in a direction opposite to the direction of tightening the male screw 200 against the female screw 201.

[0016] FIG. 6 is a graph showing, in a screw tightening device according to an embodiment, the transition of the detection value obtained by the second detector when the elevator mechanism is driven, in the form of a waveform. The vertical axis indicates the current position of the elevator mechanism 3. The horizontal axis indicates time. When the motor 2 is rotated in a direction opposite to the direction of tightening the male screw 200 against the female screw 201, the male screw 200 rises along the helix of the thread of the female screw 201, and the elevator mechanism 3 also rises in conjunction with the rise of the male screw 200. At this time, the detection value detected by the second detector 5 indicates the rise of the elevator mechanism 3. Then, when the tip of the male screw 200 passes through the cut at the upper end of the helix of the female screw 201, it is pushed down by the elevator mechanism 3 and descends. At this time, the detection value detected by the second detector 5 indicates the descent of the elevator mechanism 3. The waveform shown in FIG. 6 is the transition of the position of the elevator mechanism 3 obtained by the second detector 5 during this series of operations. The lowest point A of the waveform shown in FIG. 6 is the position where the male screw 200 and the female screw 201 mesh.

[0017] Next, a method for accurately detecting the lowest point A of the waveform, which is the position where the male screw 200 and the female screw 201 engage, will be described based on the detection value of the second detector 5. In the screw tightening device 100 according to this embodiment, in order to accurately detect the lowest point A of the waveform, the lowest point A of the lifting mechanism 3 is determined as the engagement position of the male screw 200 and the female screw 201 from the continuous change in the position of the lifting mechanism 3 detected by the second detector 5. Specifically, first, the control unit 6 calculates a moving average of the lifting mechanism 3 for a set number of times from the detection value of the second detector 5 detected at each sampling period, and removes fine noise from the waveform. Figure 7 is a graph showing the moving average line in section VII shown in Figure 6. As shown in Figure 7, the control unit 6 acquires n consecutive data from the multiple data that have been moved averaged, and takes any one data excluding the first and nth data as the mth data. That is, m is a number smaller than n. The number n shown in Figure 7 is 9 as an example. However, the number n is not limited to the 9 shown in Figure 7, but can be any other number. Also, in Figure 7, as an example, the 5th data is used as the mth data. The control unit 6 divides the n data into a first region R1 containing data P1 to the mth data P5, and a second region R2 containing data P5 to the nth data P9. In the first region R1, the difference between the first data and the second data is calculated. Then, in the first region R1, the difference between the second data and the third data is calculated. This process of calculating the difference between adjacent data is performed for all data in the first region R1. Similarly, the process of calculating the difference between adjacent data is also performed in the second region R2. As a result, if all the data in the first region R1 are trending downwards and all the data in the second region R2 are trending upwards, the position of the motor 2 when the mth data P5 is acquired will be the position where the male screw 200 and the female screw 201 are engaged. Therefore, by referencing the position of motor 2, which was stored when motor 2 was reversed, at the same timing as when the lowest point A of the lifting mechanism 3 was obtained, the position where the male screw 200 and the female screw 201 engage can be accurately determined.

[0018] Also, it is necessary not to erroneously detect a location different from the meshing position between the male screw 200 and the female screw 201. As described above, based on a plurality of moving-averaged data, the position where the screw changes from a downward trend to an upward trend is determined as the meshing position of the screw. However, as shown in part B of FIG. 6, for example, there may be a case where the trend changes from downward to upward even outside the meshing position of the screw. It is necessary to set a threshold for the difference from the selected data so as not to erroneously detect the position of the screw meshing at the positions of the downward and upward movements of the minute waveform in this part B. Specifically, when the difference D1 between the first data P1, which is the first data in the first region R1, and the m-th data P5, which is the last data, exceeds a preset threshold T1, and when the difference D2 between the m-th data P5, which is the first data in the second region R2, and the n-th data P9, which is the last data, exceeds a preset threshold T2, the control unit 6 determines that the male screw 200 and the female screw 201 are meshed. Thereby, the downward and upward movements of the minute waveform can be ignored, and the lowest point A can be detected more accurately.

[0019] Note that the second detector 5 may be an acceleration sensor that detects the acceleration of the lifting mechanism 3 instead of the means for detecting the position of the lifting mechanism 3. By providing an acceleration sensor as the second detector 5, the screw tightening device 100 becomes less expensive than, for example, an encoder or a linear scale that detects the position of the lifting mechanism 3.

[0020] Next, the screw tightening process in the screw tightening device 100 according to the embodiment will be described with reference to Figures 8 to 10. Figure 8 is a flowchart showing the screw tightening process of the screw tightening device according to the embodiment. Figure 9 is an explanatory diagram showing the periodic interrupt processing performed in the screw tightening process of the screw tightening device according to the embodiment. First, the control unit 6 permits the execution of the periodic interrupt processing (step S101). As shown in Figure 9, periodic interrupt processing is a process that is executed at regular intervals while the main routine is executing. When the execution of periodic interrupt processing is permitted in the main routine, the periodic interrupt processing is executed at regular intervals. When the periodic interrupt processing is executed, the execution of the main routine is temporarily suspended. When the periodic interrupt processing is completed, the main routine resumes from where it was suspended, and after a certain period of time has elapsed, the periodic interrupt processing occurs again. This is repeated until the execution of periodic interrupt processing is prohibited. In Embodiment 1, periodic interrupt processing is performed in order to accurately detect the position where the male screw 200 and the female screw 201 are engaged. As a result, in periodic interrupt processing, the detection value of the second detector 5 can be acquired and calculated at fixed time intervals, regardless of increases or decreases in the processing load of the main routine, thus ensuring the reproducibility of the periodic interrupt process. The periodic interrupt process executed within the periodic interrupt processing will be described later.

[0021] Next, the control unit 6 drives the motor 2 to rotate it in the reverse direction while the tip of the male screw 200 held in bit 1 is in contact with the tip of the female screw 201 (step S102). In other words, the control unit 6 rotates the motor 2 in the opposite direction to the direction in which the male screw 200 is tightened into the female screw 201. Then, the control unit 6 determines whether the tip of the male screw 200 and the tip of the female screw 201 are engaged (step S103). If the control unit 6 determines that the tip of the male screw 200 and the tip of the female screw 201 are engaged (step S103: Yes), it terminates the rotation of the motor 2 in the reverse direction (step S104) and prohibits the execution of the periodic interrupt processing (step S105). The position where the tip of the male screw 200 and the tip of the female screw 201 are engaged is set as the starting position for tightening the male screw 200. On the other hand, if the control unit 6 determines that the tip of the male screw 200 and the tip of the female screw 201 are not engaged (step S103: No), it rotates the motor 2 in the reverse direction until the tip of the male screw 200 and the tip of the female screw 201 engage.

[0022] Next, the control unit 6 calculates a value by adding a rotation amount corresponding to the effective length of the male screw 200 to the rotation position of the motor 2 detected by the first detector 4 at the position where the tip of the male screw 200 and the tip of the female screw 201 are engaged (step S106). This value becomes the seated position of the male screw 200. In this embodiment, seating means that the seating surface of the screw, i.e., the lower surface of the screw head, reaches and contacts the fastened material on which the female screw 201 is formed, and the male screw 200 is tightened against the female screw 201 with a specified torque. Then, the control unit 6 calculates a value by subtracting a certain amount of rotation from the rotation position of the motor 2 which is the seated position of the male screw 200 (step S107). This value is the position at which the rotation speed of the motor 2 is reduced, and it is just before the seated position of the male screw 200.

[0023] Next, the control unit 6 rotates the motor 2 in the screw tightening direction, rotating the male screw 200 that is engaged with the female screw 201 (step S108). At this time, the control unit 6 increases the rotation speed of the motor 2 until just before the seating position of the male screw 200, and rotates the male screw 200 at high speed to temporarily fasten the male screw 200 to the female screw 201. Next, the control unit 6 determines whether or not it has reached a position where the rotation speed of the motor 2 should be reduced based on the detected value of the first detector 4 (step S109). If the control unit 6 determines that it has reached a position where the rotation speed of the motor 2 should be reduced (step S109: Yes), it reduces the rotation speed of the motor 2 to low speed (step S110), rotates the male screw 200 at low speed until it reaches the seating position, and fully fastens the male screw 200 to the female screw 201. On the other hand, if the control unit 6 determines that the motor 2 has not yet reached the position where its rotational speed should be reduced (step S109: No), it continues to increase the rotational speed of the motor 2 and rotates the male screw 200 at high speed. Next, the control unit 6 determines, based on the value detected by the first detector 4, whether or not the male screw 200 has reached its seating position (step S111). If the control unit 6 determines that the male screw 200 has reached its seating position (step S111: Yes), it stops the rotation of the motor 2 (step S112) and ends the screw tightening process. On the other hand, if the control unit 6 determines that the male screw 200 has not yet reached its seating position (step S111: No), it rotates the motor 2 at a low speed until the male screw 200 reaches its seating position.

[0024] Figure 10 is a flowchart showing the periodic interrupt process executed in the periodic interrupt processing of the screw tightening device according to the embodiment. The periodic interrupt process is repeated at a fixed period from the time the execution of the periodic interrupt process is permitted until the execution of the periodic interrupt process is prohibited. In the periodic interrupt process, the control unit 6 obtains the address of the lifting axis of the lifting mechanism 3 and performs a process to find the lowest point A, separately from the scan time of the screw tightening program. First, when the execution of the periodic interrupt process is permitted in step S101 shown in Figure 8, the control unit 6 starts the periodic interrupt process and obtains the detected value of the second detector 5 (step S201). Then, the control unit 6 determines whether the number of detected values ​​of the second detector 5 obtained satisfies the number of samples required for moving average (step S202). If the control unit 6 determines that the number of detected values ​​of the second detector 5 obtained satisfies the number of samples required for moving average (step S202: Yes), it calculates the moving average of the lifting mechanism 3 from the obtained detected values ​​(step S203). On the other hand, if the control unit 6 determines that the number of detected values ​​from the second detector 5 acquired does not meet the number of samples required for moving average calculation (step S202: No), it terminates the periodic interrupt process.

[0025] Next, the control unit 6 determines whether the number of samples in the calculated moving average meets the specified number n (step S204). If the control unit 6 determines that the number of samples in the calculated moving average meets the specified number n (step S204: Yes), it proceeds to step S205. On the other hand, if the control unit 6 determines that the number of samples in the calculated moving average does not meet the specified number n (step S204: No), it terminates the periodic interrupt process.

[0026] Next, the control unit 6 determines whether or not it was able to detect the engagement position between the tip of the male screw 200 and the tip of the female screw 201 based on the moving-averaged data (step S205). Specifically, as shown in Figure 7, the control unit 6 acquires n consecutive data points from the multiple moving-averaged data points and divides the n data points into a first region R1 from the first data point P1 to the mth data point P5, and a second region R2 from the mth data point P5 to the nth data point P9. In the first region R1, the difference between the first data point and the second data point is calculated. Then, in the first region R1, the difference between the second data point and the third data point is calculated. This process of calculating the difference between adjacent data points is performed for all data points in the first region R1. Similarly, the process of calculating the difference between adjacent data points is also performed for the second region R2. As a result, if all the detected values ​​in the first region R1 are on a downward trend and all the detected values ​​in the second region R2 are on an upward trend, the position of motor 2 when the mth data is acquired will be the position where the male screw 200 and the female screw 201 are engaged. When the control unit 6 determines that it has been able to detect the engaged position of the tip of the male screw 200 and the tip of the female screw 201 (step S205: Yes), it stores the current detected value detected by the first detector 4 as the engaged position of the tip of the male screw 200 and the tip of the female screw 201 (step S206) and terminates the periodic interrupt process. On the other hand, when the control unit 6 determines that it has not been able to detect the engaged position of the tip of the male screw 200 and the tip of the female screw 201 (step S205: No), it terminates the periodic interrupt process. When the control unit 6 terminates the periodic interrupt process, it executes the periodic interrupt process again after a certain period of time has elapsed until the execution of the periodic interrupt process is prohibited in step S105 shown in Figure 8.

[0027] In the screw tightening device 100 according to this embodiment, the position where the male screw 200 and the female screw 201 begin to engage can be accurately detected by accurately detecting the lowest point A of the lifting mechanism 3. This reduces the variation in the amount of rotation of the motor 2 required to tighten the male screw 200. Furthermore, when tightening the male screw 200 into the female screw 201, if the male screw 200 becomes jammed into the female screw 201 midway through the tightening process, the amount of rotation of the motor 2 required to tighten the screw will decrease. In this case, the control unit 6 may be configured to determine that a screw tightening defect has occurred, where the male screw 200 became jammed into the female screw 201 midway through the tightening process, if the detected value detected by the first detector 4 is smaller than the seating position of the male screw 200, starting from the position where the male screw 200 and the female screw 201 engage. If the control unit 6 determines that a screw tightening defect has occurred, it may be configured to issue an alarm using a display device or an audio output device to notify the user.

[0028] Furthermore, the detection value of the second detector 5 indicates that the lifting mechanism 3 always moves downward when the male screw 200 is tightened into the female screw 201. Nevertheless, if the detection value of the second detector 5 indicates an upward movement, it indicates that the bit 1 is about to detach from the groove of the screw head of the male screw 200. Therefore, when the motor 2 is rotating to tighten the male screw 200 into the female screw 201, the control unit 6 determines that the bit 1 has detached from the screw head of the male screw 200 if it detects an upward movement of the lifting mechanism 3 based on the detection value of the second detector 5. When the control unit 6 determines that the bit 1 has detached from the screw head of the male screw 200, it may be configured to issue an alarm using a display device or an audio output device to notify the user. Alternatively, when the control unit 6 determines that the bit 1 has detached from the screw head of the male screw 200, it may control the lifting mechanism 3 to increase the pressing force that presses the male screw 200 against the female screw 201. This prevents bit 1 from coming out of the groove on the screw head of male screw 200, thus preventing damage to the groove on the screw head of male screw 200.

[0029] Furthermore, the second detector 5 indicates that if the lifting mechanism 3 is controlled to increase the pressing force that presses the male screw 200 against the female screw 201, it is not possible to prevent the bit 1 from disengaging from the groove in the screw head of the male screw 200. If this operation is repeated, it is highly likely that the bit 1 has spun freely multiple times in the groove in the screw head of the male screw 200, and that the groove in the screw head of the male screw 200 is damaged. In this case, the control unit 6 may determine whether there is a high probability of damage to the male screw 200 based on the value detected by the second detector 5, and if it determines that there is a high probability of damage to the male screw 200, it may be configured to issue an alarm using a display device or audio output device to notify the user.

[0030] As described above, the screw tightening device 100 according to the embodiment includes a bit 1 for tightening a male screw 200, a motor 2 for rotating the bit 1, a lifting mechanism 3 for raising and lowering the motor 2, a first detector 4 for detecting the rotational position of the motor 2, a second detector 5 for detecting the position or acceleration of the lifting mechanism 3, and a control unit 6 for controlling the motor 2 and the lifting mechanism 3. When the motor 2 is rotated in the opposite direction to the screw tightening direction with the male screw 200 held in bit 1 in contact with the female screw 201, the control unit 6 determines the lowest point A of the lifting mechanism 3 as the engagement position between the male screw 200 and the female screw 201 from the continuous change in the position of the lifting mechanism 3 detected by the second detector 5. At the engagement position between the male screw 200 and the female screw 201, the control unit 6 calculates the screw seating position by adding the amount of rotation of the motor 2 corresponding to the effective length of the male screw 200 to the rotation position of the motor 2 detected by the first detector 4. Based on the value detected by the first detector 4, the control unit 6 increases the rotation speed of the motor 2 to high speed until just before the screw seating position to temporarily tighten the male screw 200 into the female screw 201, and then controls the motor 2 to low speed to fully tighten the male screw 200 into the female screw 201.

[0031] Therefore, the screw tightening device 100 according to this embodiment determines the lowest point A of the lifting mechanism 3 as the engagement position between the male screw 200 and the female screw 201 based on the continuous change in the position of the lifting mechanism 3 detected by the second detector 5. This allows for accurate detection of the engagement position between the tip of the male screw 200 and the tip of the female screw 201 when tightening the male screw 200 into the female screw 201. In other words, it is possible to suppress variations in the amount of rotation of the motor 2 from the time the motor 2 starts rotating in the direction of tightening the screw until the male screw 200 seats on the female screw 201. Furthermore, the control unit 6 controls the motor 2 to temporarily tighten the male screw 200 into the female screw 201 by increasing the rotation speed of the motor 2 until just before the screw seating position, and then reduces the rotation speed of the motor 2 to fully tighten the male screw 200 into the female screw 201. This suppresses overshoot of the male screw 200 due to torque exceeding expectations and shortens the time required for screw tightening.

[0032] The configurations shown in the above embodiments are examples and can be combined with other known technologies. Furthermore, it is possible to omit or modify parts of the configuration without departing from the spirit of the invention.

[0033] The various aspects of this disclosure are summarized below as an appendix.

[0034] (Note 1) A screw fastening device used for fastening a male screw into a female screw, A bit for tightening the aforementioned male screw, A motor for rotating the aforementioned bit, A lifting mechanism for raising and lowering the motor, A first detector for detecting the rotational position of the motor, A second detector for detecting the position or acceleration of the lifting mechanism, The system comprises a control unit that controls the motor and the lifting mechanism, The control unit, with the male screw held in the bit in contact with the female screw, rotates the motor in the opposite direction to the screw tightening direction, and determines the lowest point of the lifting mechanism as the engagement position between the male screw and the female screw based on the continuous change in position or acceleration of the lifting mechanism detected by the second detector. The control unit calculates the screw seating position by adding the amount of rotation of the motor corresponding to the effective length of the male screw to the rotation position of the motor detected by the first detector at the engagement position between the male screw and the female screw. Based on the value detected by the first detector, the control unit increases the rotation speed of the motor to high speed to temporarily tighten the male screw into the female screw until just before the screw seating position, and then controls the motor to low speed to fully tighten the male screw into the female screw. A screw tightening device characterized by the following features. (Note 2) The control unit calculates a moving average of the lifting mechanism from the detected values ​​of the second detector detected at each sampling period, obtains n consecutive data points from the multiple moving-averaged data points, divides the n data points into a first region from the first data point to the mth data point which is a value less than n, and a second region from the mth data point to the nth data point. If the difference between adjacent data points in the first region is all on a downward trend, and the difference between adjacent data points in the second region is all on an upward trend, the control unit determines that the position of the motor when the mth data point is obtained is the position where the male screw and the female screw are engaged. The screw tightening device described in Appendix 1, characterized by the features described herein. (Note 3) The control unit determines that the male screw and the female screw are engaged only if the difference between the first data and the last data in the first region exceeds a preset threshold, and the difference between the first data and the last data in the second region also exceeds a preset threshold. The screw tightening device described in Appendix 2, characterized by the features described herein. (Note 4) The control unit determines that if the detected value from the first detector is smaller than the seating position of the male screw, starting from the position where the male screw and the female screw engage, a screw tightening defect has occurred where the male screw has jammed into the female screw during the tightening process. A screw tightening device as described in any one of the appendices 1 to 3, characterized by the features described herein. (Note 5) When the control unit rotates the motor to screw the male screw into the female screw, and the second detector detects an upward movement of the lifting mechanism, the control unit determines that the bit has detached from the screw head of the male screw. A screw tightening device as described in any one of the appendices 1 to 4, characterized by the features described herein. (Note 6) When the control unit determines that the bit has detached from the screw head of the male screw, it controls the lifting mechanism to increase the pressing force that presses the male screw against the female screw. The screw tightening device described in Appendix 5, characterized by the features described herein. [Explanation of Symbols]

[0035] 1 bit, 2 motor, 3 lifting mechanism, 4 first detector, 5 second detector, 6 control unit, 100 screw tightening device, 200 male screw, 201 female screw.

Claims

1. A screw fastening device used for fastening a male screw into a female screw, A bit for tightening the aforementioned male screw, A motor for rotating the aforementioned bit, A lifting mechanism for raising and lowering the motor, A first detector for detecting the rotational position of the motor, A second detector for detecting the position or acceleration of the lifting mechanism, The system comprises a control unit that controls the motor and the lifting mechanism, The control unit, with the male screw held in the bit in contact with the female screw, rotates the motor in the opposite direction to the screw tightening direction. Based on the continuous change in position or acceleration of the lifting mechanism detected by the second detector, the control unit determines the lowest point of the lifting mechanism as the engagement position between the male screw and the female screw. At the engagement position between the male screw and the female screw, the control unit calculates the screw seating position by adding the amount of rotation of the motor corresponding to the effective length of the male screw to the rotation position of the motor detected by the first detector. Based on the value detected by the first detector, the control unit increases the rotation speed of the motor to a high speed to temporarily tighten the male screw into the female screw until just before the screw seating position, and then controls the motor to a low speed to fully tighten the male screw into the female screw. A screw tightening device characterized by the following features.

2. The control unit calculates a moving average of the lifting mechanism from the detected values ​​of the second detector detected at each sampling period for a set number of times, acquires n consecutive data points from the multiple moving-averaged data points, divides the n data points into a first region from the first data point to the mth data point which is a value less than n, and a second region from the mth data point to the nth data point, and determines that the position of the motor when the mth data point is acquired is the position where the male screw and the female screw are engaged. The screw tightening device according to feature 1.

3. The control unit determines that the male screw and the female screw are engaged only if the difference between the first data and the last data in the first region exceeds a preset threshold, and the difference between the first data and the last data in the second region also exceeds a preset threshold. The screw tightening device according to feature 2.

4. The control unit determines that if the detected value from the first detector is smaller than the seating position of the male screw, starting from the position where the male screw and the female screw engage, a screw tightening defect has occurred where the male screw has jammed into the female screw during the tightening process. A screw tightening device according to any one of claims 1 to 3.

5. When the control unit rotates the motor to screw the male screw into the female screw, if it detects an upward movement of the lifting mechanism based on the detected value from the second detector, it determines that the bit has detached from the screw head of the male screw. A screw tightening device according to any one of claims 1 to 3.

6. When the control unit determines that the bit has detached from the screw head of the male screw, it controls the lifting mechanism to increase the pressing force that presses the male screw against the female screw. The screw tightening device according to feature 5.

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