Screw tightening defect detection device

Abstract

To determine whether a failure has occurred in screw tightening or not even when a tapping screw is used for a soft material.SOLUTION: A PLC (10) includes a determination unit (13) that generates, for a data string of rotation torque consisting of a predetermined number of data points, a data string of a normalized torque serving as an amount of change relative to rotation torque at an initial data point of the data string and that, based on the data string of the normalized torque, determines whether a defect has occurred in screw tightening or not.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a screw tightening defect determination device. [Background technology]

[0002] Patent Document 1 discloses a screw-tightening state detection device for an electric rotating tool, which has a clutch mechanism that includes a cylindrical casing that houses a spring that elastically supports a steel ball that engages with an internal gear of a reduction mechanism, a torque adjustment mechanism that includes an externally operable adjustment screw that adjusts the elasticity of the spring inside the cylindrical casing, and a torque detection element on the outer surface of the cylindrical casing.

[0003] The screw tightening state detection device of an electric rotating tool described in Cited Document 1 can determine whether a screw tightening state is good or bad by converting a detection value of an output signal detected by a torque detection element during a screw tightening operation into a torque value based on the detection value. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-147317 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a tapping screw is used for a soft material (workpiece) such as resin, for example, a phenomenon may occur in which the tip of the tapping screw advances from the bottom of the workpiece during pre-tightening, which is the process until the seating surface of the tapping screw contacts the workpiece, due to an incorrect screw length or poor formation of the workpiece. In this case, for example, the torque value required from pre-tightening of the tapping screw to final tightening, which is the process after the seating surface of the tapping screw contacts the workpiece, differs. However, the torque value varies for each workpiece. For this reason, it was difficult to determine whether the tapping screw had normally reached the bottom by simply judging the quality of the screw tightening state based on the torque value in the screw tightening state detection device for the electric rotating tool described in Patent Document 1.

[0006] One aspect of the present invention aims to provide a screw tightening defect determination device that can determine whether or not a defect has occurred in the screw tightening even when a tapping screw is used on a soft material. [Means for solving the problem]

[0007] In order to solve the above problems, a screw tightening defect determination device according to one embodiment of the present invention generates a data string of normalized torque, which is the amount of change relative to the rotational torque at the first data point in a data string consisting of a predetermined number of data points obtained by sampling the rotational torque of a motor that generates a rotational motion around an axis of a driver for tightening a screw, at a predetermined period, with the data point at the end where the rotational torque is equal to or greater than a predetermined first threshold value, and determines whether a screw tightening defect has occurred based on the data string of normalized torque.

[0008] According to the above configuration, it is possible to determine whether a defect has occurred in the screw tightening by comparing the data string of the normalized torque with, for example, the data string of the torque in an abnormal state. Therefore, for example, when a tapping screw is used for a soft material, even in a situation where the torque value varies for each workpiece, it is possible to determine whether a defect has occurred in the screw tightening.

[0009] In addition, in a screw tightening defect judgment device according to one embodiment of the present invention, it is preferable that the judgment unit judges that a defect has occurred in the screw tightening when the normalized torque at a data point at a predetermined position in the data string of the normalized torque is equal to or greater than a predetermined second threshold value.

[0010] According to the above configuration, it is possible to determine whether a defect has occurred in the screw tightening by determining whether the normalized torque at a data point at a predetermined position in the data string of normalized torque is equal to or greater than the second threshold value.

[0011] In addition, a learning device according to one embodiment of the present invention determines one or more of the specified number, the specified position, and the specified second threshold value in the screw tightening defect judgment device through learning based on learning data including a data string of the normalized torque and a normal or defective judgment result for the normalized torque data string, and outputs the determined specified number, the specified position, or the specified second threshold value to the screw tightening defect judgment device.

[0012] According to the above configuration, it is possible to appropriately determine whether a defect has occurred in the screw tightening based on the predetermined number, the predetermined position, or the second threshold value determined by learning.

[0013] In addition, it is preferable that the learning device of one embodiment of the present invention updates one or more of the specified number, the specified position, and the specified second threshold value through learning based on the data string of the normalized torque in the screw tightening and the judgment result by the judgment unit when a specified number of judgments are made by the judgment unit, a specified period of time has elapsed, or an external instruction is received.

[0014] According to the above configuration, it is possible to more appropriately determine that a defect has occurred in the screw tightening based on the updated predetermined number, the predetermined position, or the second threshold value.

[0015] In addition, in a screw tightening defect judgment device according to one embodiment of the present invention, it is preferable that the judgment unit judges that a defect has occurred in the screw tightening when the sum of the normalized torque at a predetermined range of data points in the data string of the normalized torque is equal to or greater than a predetermined third threshold value.

[0016] According to the above configuration, it is possible to determine whether a defect has occurred in the screw tightening by determining whether the sum of the normalized torques at a predetermined range of data points in the data string of normalized torque is equal to or greater than a third threshold value.

[0017] In addition, a learning device according to one embodiment of the present invention determines one or more of the specified number, the specified range, and the specified third threshold value in the screw tightening defect judgment device through learning based on a data string of the normalized torque and learning data including a normal or defective judgment result for the normalized torque data string, and outputs the determined specified number, the specified range, or the specified third threshold value to the screw tightening defect judgment device.

[0018] According to the above configuration, it is possible to appropriately determine whether a defect has occurred in the screw tightening based on the predetermined number, the predetermined range, or the third threshold value determined by learning.

[0019] In addition, a learning device according to one embodiment of the present invention may update one or more of the specified number, the specified range, and the specified third threshold value through learning based on a data string of the normalized torque in the screw tightening and the judgment result by the judgment unit when a specified number of judgments are made by the judgment unit, a specified period of time has elapsed, or an external instruction is received.

[0020] According to the above configuration, it is possible to more appropriately determine that a defect has occurred in the screw tightening, based on the updated predetermined number, the predetermined range, or the third threshold value. Effect of the Invention

[0021] According to the screw tightening defect determination device according to one aspect of the present invention, it is possible to determine whether or not a defect has occurred in the screw tightening even when a tapping screw is used on a soft material. [Brief description of the drawings]

[0022] [Figure 1] 1 is a block diagram showing an overview of a screw tightening system according to an embodiment of the present invention. [Diagram 2] 1 is a block diagram showing a configuration of a PLC according to an embodiment of the present invention. [Diagram 3] 1 is a diagram showing an example of the appearance of a screw tightening system according to an embodiment of the present invention; [Figure 4] FIG. 4 is a diagram showing a data string of normalized torque according to the embodiment. [Diagram 5] 6 is a flowchart showing an example of a screw tightening defect determination process according to the embodiment. [Figure 6] FIG. 13 is a block diagram showing the configuration of a PLC and a learning device according to a modified example of the present embodiment. [Figure 7] 10 is a flowchart showing an example of a screw tightening defect determination process according to a modified example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment according to one aspect of the present invention (hereinafter also referred to as "the present embodiment") will be described with reference to the drawings.

[0024] §1 Examples of application Fig. 1 is a block diagram showing an overview of a screw fastening system 1 according to this embodiment. As shown in Fig. 1, the screw fastening system 1 includes a PLC (Programmable Logic Controller) 10 (screw fastening defect determination device), a coupler 20, a rotation servo 30 (first motor), and a reciprocating servo 40 (second motor). The screw fastening system 1 performs a screw fastening operation by a rotational motion around an axis and a reciprocating motion in the axial direction of a driver 51 (see Fig. 3), which will be described later. At this time, the PLC 10 controls the screw fastening operation and determines the occurrence of a defect in the screw fastening operation.

[0025] In this specification, a fault in a screw tightening operation refers to bottoming out, which occurs when a screw reaches the bottom of a screw hole before the screw tightening is complete due to the screw being longer than the screw hole or due to poor formation of the workpiece.

[0026] The rotation servo 30 is a motor that generates a rotational motion around the axis of the driver 51. The rotation servo 30 also outputs its own rotation speed (deg. / s), rotation amount (deg.), and rotation torque (proportion (%) of rated torque) to the coupler 20. Specifically, the rotation servo 30 outputs data points obtained by sampling its own rotation speed, rotation amount, and rotation torque at a predetermined period to the coupler 20.

[0027] The reciprocating servo 40 is a motor that generates a reciprocating motion in the axial direction of the driver 51. The reciprocating servo 40 also outputs to the coupler 20 the moving speed (mm / s), moving position (mm), and moving torque (proportion (%) of the rated torque) of the driver 51 caused by its own rotation.

[0028] The coupler 20 connects the PLC 10 with the rotation servo 30 and the reciprocating servo 40. In particular, the coupler 20 transmits a control signal received from the PLC 10 to the rotation servo 30 and the reciprocating servo 40. The coupler 20 also transmits data points obtained by sampling the rotation speed, rotation amount, and rotation torque of the rotation servo 30 at a predetermined period, which are received from the rotation servo 30, to the PLC 10. The coupler 20 also transmits the moving speed, moving position, and moving torque of the driver 51 caused by the rotation of the reciprocating servo 40, which are received from the reciprocating servo 40, to the PLC 10.

[0029] In the following description, the rotation speed, rotation amount, rotation torque, and data string of the rotation torque of the rotation servo 30, as well as the movement speed, movement position, and movement torque of the driver 51 due to the rotation of the reciprocating servo 40, may be collectively referred to as parameters.

[0030] 2 is a block diagram showing the configuration of the PLC 10. The PLC 10 controls the operation of the screw tightening system 1. As shown in FIG. 2, the PLC 10 includes a control unit 11, a communication unit 12, and a determination unit 13.

[0031] The control unit 11 outputs control signals for controlling the rotation servo 30 and the reciprocating servo 40 to the communication unit 12. The communication unit 12 transmits the control signals input from the control unit 11 to the coupler 20. The control signals are transmitted to the rotation servo 30 and the reciprocating servo 40 via the coupler 20, and control the rotation servo 30 and the reciprocating servo 40. The control unit 11 controls the rotation servo 30 and the reciprocating servo 40 in synchronization with each other. The control unit 11 also feeds back parameters of the rotation servo 30 and the reciprocating servo 40 to the control of the rotation servo 30 and the reciprocating servo 40.

[0032] The communication unit 12 receives parameters from the rotation servo 30 and the reciprocation servo 40 via the coupler 20. The control unit 11 and the determination unit 13 acquire parameters from the coupler 20 via the communication unit 12 as necessary.

[0033] The judgment unit 13 judges whether or not a defect has occurred in the screw fastening. The contents of the judgment by the judgment unit 13 will be described later.

[0034] The screw tightening system 1 further includes an alarm device (not shown). When the judgment unit 13 judges that a defect has occurred in the screw tightening, the judgment result is output by the alarm device. The alarm device is, for example, a speaker that outputs a sound indicating the judgment result, or a display that displays an image indicating the judgment result.

[0035] §2 Configuration Example (Screw tightening system 1 configuration) Fig. 3 is a diagram showing an example of the appearance of the screw fastening system 1 according to this embodiment. As shown in Fig. 3, the screw fastening system 1 includes a rotation servo 30, a reciprocating servo 40, a driver unit 50, and a support 60. Although not shown in Fig. 3, the screw fastening system 1 also includes a PLC 10 and a coupler 20 as described above.

[0036] The driver unit 50 is a unit for tightening screws. The driver unit 50 includes a driver 51 and a screw holding portion 52. The driver 51 performs a screw tightening operation by reciprocating in the axial direction while rotating around its axis. In the following description, the direction in the axial direction of the driver 51 that the driver 51 moves in the process of tightening a screw is referred to as downward.

[0037] The rotation servo 30 is disposed above the driver 51, and generates a rotational motion about the axis of the driver 51. In addition, the screw holding part 52 is provided below the driver 51, and holds the screw to be tightened by the driver 51.

[0038] The support 60 supports the driver unit 50 so that it can move up and down. The reciprocating servo 40 is provided on the upper part of the support 60 and is connected to the driver unit 50 via a ball screw (not shown). The rotational motion of the reciprocating servo 40 is converted into linear motion in the vertical direction by the ball screw. As a result, the driver unit 50 reciprocates up and down.

[0039] (Screw tightening operation) The operation of the screw tightening system 1 for tightening a screw is as follows. First, the screw holding unit 52, which holds a screw, lowers the screw to the location of the workpiece (not shown) made of resin, where the screw is to be tightened. However, the workpiece is not limited to resin, as long as it is a soft material. Next, the driver 51 presses the screw against the location where the screw is to be tightened while rotating it, until the screw is provisionally seated. Here, provisional seating refers to a state in which the bearing surface of the screw is in contact with the workpiece.

[0040] The screw tightening system 1 performs final tightening by pressing the screw against the screw while rotating it further from the state where the screw is temporarily seated. In this embodiment, the final tightening is performed until the rotation torque of the rotation servo 30 reaches a predetermined final tightening completion value. When the rotation torque reaches the final tightening completion value, the screw tightening system 1 stops pressing the screw and maintains the state where the rotation torque is equal to or greater than the final tightening completion value for 100 ms.

[0041] Thereafter, the screw fastening system 1 releases the screw by making the rotation torque of the rotation servo 30 0% or less. Furthermore, the screw fastening system 1 completes the screw fastening operation by moving the driver 51 upward and returning it to its original position. Note, however, that the above-mentioned rotation torque and holding time are merely examples and will vary depending on the type of screw and the type of fastening object / object to be fastened.

[0042] (Screw tightening failure judgment operation) Specifically, the determination unit 13 acquires data points of the rotational torque from the coupler 20 via the communication unit 12. Next, the determination unit 13 generates a data string of normalized torque for a data string of rotational torque consisting of a predetermined number of data points, the last of which is a data point at which the rotational torque is equal to or greater than a predetermined first threshold value, among the acquired data points. Here, the data string of normalized torque refers to the amount of change in rotational torque at each data point relative to the rotational torque at the first data point in the data string of rotational torque. The first threshold value is a predetermined value for the rotational torque of the rotation servo 30 when the screw tightening system 1 completes the provisional tightening of the screw and starts the final tightening.

[0043] The determination unit 13 obtains a second threshold value from a storage device (not shown). Here, the second threshold value is a predetermined threshold value for determining that a defect has occurred in the screw fastening for the normalized torque value at a data point at a predetermined position in the data string of the normalized torque.

[0044] The determination unit 13 determines that a defect has occurred in the screw tightening when the normalized torque at a data point at a predetermined position in the data string of the normalized torque is equal to or greater than a predetermined second threshold value. In this way, the determination unit 13 can determine that a defect has occurred in the screw tightening by determining whether the normalized torque at a data point at a predetermined position in the data string of the normalized torque is equal to or greater than the second threshold value.

[0045] The determination unit 13 may obtain the third threshold value from a storage device (not shown). Here, the third threshold value is a predetermined threshold value for determining that a defect has occurred in the screw fastening for the total value of the normalized torque at data points in a predetermined range in the data string of the normalized torque.

[0046] In this case, the determination unit 13 determines that a defect has occurred in the screw tightening when the sum of the normalized torques at data points in a predetermined range in the data string of the normalized torque is equal to or greater than the third threshold value. Thus, the determination unit 13 can determine that a defect has occurred in the screw tightening by determining whether the sum of the normalized torques at data points in a predetermined range in the data string of the normalized torque is equal to or greater than the third threshold value.

[0047] FIG. 4 is a diagram showing a data string of normalized torque according to this embodiment. The horizontal axis of FIG. 4 indicates data points (sampling time), and the vertical axis indicates the value of normalized torque. Th2 on the vertical axis of FIG. 4 indicates a second threshold value. In the example shown in FIG. 4, the number of data points included in the data string of normalized torque is 51, and the predetermined position is the 43rd position from the beginning of the data string. Therefore, when the normalized torque at the 43rd data point is equal to or greater than Th2, the judgment unit 13 judges that a defect has occurred in the screw tightening. In FIG. 4, data on 50 screws that were normally tightened is shown in black, and data on 32 screws that were abnormal is shown in gray. In the data of the normal screws, the normalized torque at the 43rd data point was all less than Th2. On the other hand, in the data of the abnormal screws, the torque increase occurs due to the screw progressing beyond the bottom of the screw hole, so the normalized torque at the 43rd data point was all equal to or greater than Th2. Therefore, according to the above judgment, a defect in the screw tightening can be appropriately judged. In addition, with the non-normalized torque (raw data) before the starting point is aligned, there is a large variation in torque for each workpiece, so it is not possible to distinguish between normal and abnormal conditions using a single threshold value.

[0048] The specific value of the second threshold value may be appropriately set to a value that allows for determining whether the screw tightening is normal or not. The number of data points to be included in the data string of the normalized torque is not limited to 51, and may be appropriately set. The predetermined position is not limited to the 43rd position, and may be appropriately set to a position that allows for determining whether the screw tightening is normal or not using the second threshold value. The same applies to the specific value of the third threshold value and the specific range of data points for calculating the total value of the normalized torque when the determination unit 13 makes a determination using the third threshold value.

[0049] In the above-mentioned example of the screw tightening operation, the screw tightening system 1 tightens a screw into a workpiece in a state where a female thread is not yet cut at the location where the screw is to be tightened (tapping (self-tapping)). However, the screw tightening system 1 can also tighten a screw into a workpiece in a state where a female thread is already cut at the location where the screw is to be tightened (tapping).

[0050] §3 Example of operation 5 is a flow chart showing an example of the screw tightening defect determination process according to the present embodiment. The determination of the occurrence of a defect in the screw tightening operation by the determination unit 13 will be described with reference to FIG.

[0051] As shown in FIG. 5, the determination unit 13 acquires a data string of rotational torque from the coupler 20 via the communication unit 12 (S1). Next, the determination unit 13 generates a data string of normalized torque (S2). Next, the determination unit 13 acquires a second threshold value from the storage device, and determines whether the normalized torque at a data point at a predetermined position in the data string of normalized torque is equal to or greater than the second threshold value (S3). If the normalized torque is equal to or greater than the second threshold value (YES in S3), the determination unit 13 outputs an alarm signal indicating that the screw tightening is defective to the alarm device (S4). If the normalized torque is not equal to or greater than the second threshold value (NO in S3), the determination unit 13 ends the process without executing step S4.

[0052] Note that the determination unit 13 may obtain a third threshold value from the storage device in step S3, and determine whether the sum of the normalized torques at data points in a predetermined range in the data string of normalized torques is equal to or greater than the third threshold value.

[0053] § 4 Variations Although the embodiment of the present invention has been described in detail above, the above description is merely an example of the present invention in every respect. It goes without saying that various improvements and modifications can be made without departing from the scope of the present invention. For example, the following modifications are possible. In the following, the same reference numerals are used for the same components as in the above embodiment, and the description of the same points as in the above embodiment is omitted as appropriate. The following modifications can be combined as appropriate.

[0054] The screw tightening system according to this modification includes a learning unit 70 (learning device) in addition to the components of the screw tightening system 1. The learning unit 70 is configured to be able to perform machine learning, and is, for example, a personal computer, a smartphone, a mobile information terminal, or a server.

[0055] 6 is a block diagram showing the configuration of the PLC 10 and the learning device according to this modification. As shown in FIG. 6, in this modification, the learning unit 70 is connected to the determination unit 13.

[0056] The learning unit 70 determines one or more of the predetermined number, the predetermined position, and the second threshold value in the PLC 10 by learning, based on the learning data including the data sequence of the normalized torque and the result of the determination of normal or defective for the data sequence of the normalized torque. However, the learning unit 70 may determine one or more of the predetermined number, the predetermined range, and the third threshold value in the PLC 10 by learning, based on the learning data including the data sequence of the normalized torque and the result of the determination of normal or defective for the data sequence of the normalized torque. In this embodiment, the learning unit 70 determines all of the predetermined number, the predetermined position, and the second threshold value in the PLC 10 by learning, based on the learning data including the data sequence of the normalized torque and the result of the determination of normal or defective for the data sequence of the normalized torque.

[0057] Here, learning means machine learning, and refers to supervised learning. As an algorithm for supervised learning, for example, a neural network, an isolation forest, or a support vector machine is used. The learning unit 70 may also calculate the anomaly score using a probability density function and a kernelized probability model. The probability density function is, for example, a normal distribution, but is not limited to this.

[0058] The learning unit 70 outputs the determined predetermined number, the determined position, or the second threshold value to the judgment unit 13 included in the PLC 10. As a result, the judgment unit 13 can judge that a defect has occurred in the screw tightening based on the determined predetermined number, the determined position, or the second threshold value. However, the learning unit 70 may output the determined predetermined number, the determined range, or the third threshold value to the judgment unit 13 included in the PLC 10. In this embodiment, the learning unit 70 outputs the determined predetermined number, the determined position, and the second threshold value to the judgment unit 13 included in the PLC 10. As a result, the judgment unit 13 can judge that a defect has occurred in the screw tightening based on the determined predetermined number, the determined position, and the second threshold value learned by the learning unit 70. In the case where the learning unit 70 does not determine one or more of the predetermined number, the determined position, and the second threshold value by learning, the values ​​that are not determined may be stored in advance in the storage device.

[0059] The learning unit 70 updates one or more of the predetermined number, the predetermined position, and the second threshold value by learning based on the data sequence of the normalized torque in screw tightening and the judgment result by the judgment unit when the judgment unit 13 judges a predetermined number of times, a predetermined period has elapsed, or an external instruction is received. This allows the judgment unit 13 to judge that a defect has occurred in the screw tightening based on the updated predetermined number, the predetermined position, or the second threshold value. However, the learning unit 70 may update one or more of the predetermined number, the predetermined range, and the third threshold value by learning based on the data sequence of the normalized torque in screw tightening and the judgment result by the judgment unit when the judgment unit 13 judges a predetermined number of times, a predetermined period has elapsed, or an external instruction is received. In this embodiment, the learning unit 70 updates all of the predetermined number, the predetermined position, and the second threshold value by learning based on the data sequence of the normalized torque in screw tightening and the judgment result by the judgment unit when the learning start condition is satisfied. This enables the determination unit 13 to determine that a defect has occurred in the screw fastening, based on the updated predetermined number, the predetermined position, and the second threshold value.

[0060] FIG. 7 is a flow chart showing an example of a screw tightening defect judgment process according to this modified example. The judgment of the occurrence of a defect in the screw tightening operation by the judgment unit 13 and the learning unit 70 will be described below with reference to FIG. 7. As shown in FIG. 7, the judgment unit 13 performs the processes from S1 to S5. The processes from S1 to S4 by the judgment unit 13 are the same as those described above, and therefore will not be described. If the normalized torque is not equal to or greater than the second threshold value (NO in S3), or after outputting a notification signal indicating that the screw tightening is defective to the notification device (S4), the judgment unit 13 outputs data of the judgment result to the learning unit 70 (S5). Specifically, the judgment unit 13 outputs learning data including a data string of the normalized torque and a judgment result of normal or defective for the data string of the normalized torque to the learning unit 70. Then, the judgment unit 13 ends the process of judging the occurrence of a defect.

[0061] The learning unit 70 determines whether a learning start condition is met (S11). The learning start condition is, for example, (i) immediately after the start of processing by the learning unit 70; (ii) the determination unit 13 performs a predetermined number of determinations; (iii) A specified period of time has elapsed since the last time the condition for starting studies was met; and (iv) Receiving instructions from outside to start learning When any one of these conditions is satisfied, the learning unit 70 determines that the learning start condition is satisfied. However, the learning start conditions are not limited to these. Also, one or more of these conditions may not be set as the learning start condition.

[0062] If the condition for starting learning is not satisfied (NO in S11), the learning unit 70 repeats step S11 until the condition for starting learning is satisfied. If the condition for starting learning is satisfied (YES in S11), the learning unit 70 acquires learning data (S12). If the processing of the learning unit 70 has just started, the learning data is teacher data stored in the storage device. In other cases, the learning data is learning data stored in the storage device by the judgment unit 13 in step S5. Next, the learning unit 70 determines a predetermined number in the PLC 10 by learning based on the learning data, and outputs the predetermined number to the judgment unit 13 (S13). Next, the judgment unit 13 determines a predetermined position and a second threshold value in the PLC 10 by learning based on the learning data, and outputs the predetermined position and the second threshold value to the judgment unit 13 (S14). Then, the learning unit 70 ends the learning process.

[0063] In addition, when the judgment unit 13 makes a judgment based on the third threshold value in S3, the judgment unit 13 may determine a predetermined range and the third threshold value in PLC 10 by learning based on the learning data in S14, and output the predetermined range and the third threshold value to the judgment unit 13.

[0064] [Software implementation example] The control block (particularly the determination unit 13) of the PLC 10 and the learning unit 70 may be realized by a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like, or may be realized by software.

[0065] In the latter case, the PLC 10 includes a computer that executes instructions of a program, which is software that realizes each function. The computer includes, for example, one or more processors, and a computer-readable recording medium that stores the program. The object of the present invention is achieved by the processor reading the program from the recording medium and executing it in the computer. The processor may be, for example, a CPU (Central Processing Unit). The recording medium may be a "non-transient tangible medium," such as a ROM (Read Only Memory), a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like. The computer may further include a RAM (Random Access Memory) that expands the program. The program may be supplied to the computer via any transmission medium (such as a communication network or a broadcast wave) that can transmit the program. Note that one aspect of the present invention may also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.

[0066] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0067] 1 Screw Fastening System 10 PLC (Screw tightening defect judgment device) 30 Rotation servo (first motor) 40 Reciprocating servo (second motor) 51 Driver 70 Learning unit (learning device)

Claims

1. a data string of normalized torque, which is the amount of change in the rotational torque at each data point relative to the rotational torque at the first data point in the data string, is generated for the data string of rotational torque consisting of a predetermined number of data points, the data points being obtained by sampling the rotational torque of a motor that generates a rotational motion around an axis of a screwdriver for tightening a screw, the data string including a data point at which the rotational torque is equal to or greater than a predetermined first threshold value; a determination unit that determines whether or not a defect occurs in the screw tightening based on the data string of the normalized torque, A screw tightening defect judgment device in which the predetermined number is determined by learning based on learning data including a data string of the normalized torque and a judgment result of normal or defective for the normalized torque data string.

2. The screw tightening defect judgment device according to claim 1, wherein the judgment unit judges that a defect has occurred in the screw tightening when the normalized torque at a data point at a predetermined position in the data string of the normalized torque is equal to or greater than a predetermined second threshold value.

3. Based on learning data including the data string of the normalized torque and a normal or defective judgment result for the data string of the normalized torque, one or more of the predetermined number, the predetermined position, and the predetermined second threshold value in the screw tightening defect judgment device according to claim 2 is determined by learning; A learning device that outputs the determined predetermined number, the predetermined position, or the predetermined second threshold value to the screw tightening defect judgment device.

4. The learning device described in claim 3, wherein when a predetermined number of judgments are made by the judgment unit, a predetermined period of time has elapsed, or an external instruction is received, one or more of the predetermined number, the predetermined position, and the predetermined second threshold value are updated through learning based on a data string of the normalized torque in the screw tightening and the judgment result by the judgment unit.

5. The screw tightening defect judgment device according to claim 1, wherein the judgment unit judges that a defect has occurred in the screw tightening when the sum of the normalized torque at a predetermined range of data points in the data string of the normalized torque is equal to or greater than a predetermined third threshold value.

6. Based on the data string of the normalized torque and learning data including a normal or defective judgment result for the data string of the normalized torque, one or more of the predetermined number, the predetermined range, and the predetermined third threshold value in the screw tightening defect judgment device according to claim 5 is determined by learning; A learning device that outputs the determined predetermined number, the predetermined range, or the predetermined third threshold value to the screw tightening defect judgment device.

7. The learning device described in claim 6, wherein when a predetermined number of judgments are made by the judgment unit, a predetermined period of time has elapsed, or an external instruction is received, one or more of the predetermined number, the predetermined range, and the predetermined third threshold value are updated through learning based on the data string of the normalized torque in the screw tightening and the judgment result by the judgment unit.

Images