Fastening device and fastening method

Abstract

To provide a fastening device and a fastening method which monitor displacement of a fastening torque, and can perform fastening while preventing twisted breakage of workpiece.SOLUTION: A fastening device 10 having a motor 12 for rotating a socket 20 with which workpiece can be mounted includes: torque measurement means 31 for acquiring a fastening torque of the workpiece for each predetermined time; difference calculation means 43 for sequentially calculating a difference between a plurality of fastening torques acquired by the torque measurement means; difference monitoring means 44 for monitoring the difference sequentially calculated by the difference calculation means, and issuing a stop command of the motor when determining that the difference satisfies a predetermined condition; and motor control means 42 for receiving the stop command of the difference monitoring means, and stopping the motor.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a device and method for fastening a workpiece such as a bolt or a screw, and more specifically to a device and method for fastening a workpiece that can prevent thread stripping of the workpiece. [Background technology]

[0002] Powered tightening devices such as electric torque wrenches are used to tighten workpieces (fastening members) such as bolts, nuts, and screws. Known tightening methods for these tightening devices include the torque method and the angle method.

[0003] In the torque method, the tightening device is equipped with a torque measuring means, and when the tightening torque reaches a preset control torque, the motor is stopped and tightening is completed (for example, see Patent Document 1).In the angle method, the tightening device is further equipped with an angle detection means such as an encoder, and tightening is performed by the torque method until the snug point after tightening starts, and thereafter the motor is rotated by a preset control rotation angle to complete tightening (for example, see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 60-14675 [Patent Document 2] Special Publication No. 61-5857 Summary of the Invention [Problem to be solved by the invention]

[0005] Regardless of whether the tightening method is the torque method or the angle method described above, if there is an abnormality in the workpiece itself, such as a decrease in the torque coefficient value, the axial force may increase before the specified control torque or control rotation angle is reached, causing the workpiece to break (fracture).

[0006] An object of the present invention is to provide a tightening device and a tightening method capable of monitoring the change in the tightening torque and performing tightening while preventing the workpiece from being stripped. [Means for solving the problem]

[0007] The tightening device of the present invention comprises: A fastening device having a motor that rotates a socket to which a workpiece can be attached, a torque measuring means for acquiring the fastening torque of the workpiece at predetermined time intervals; A difference calculation means for sequentially calculating a difference between the plurality of tightening torques acquired by the torque measurement means; a difference monitoring means for monitoring the difference successively calculated by the difference calculation means, and issuing a command to stop the motor when it is determined that the difference satisfies a predetermined condition; a motor control means for stopping the motor upon receiving the stop command from the difference monitoring means; Contains:

[0008] The fastening device of the present invention further comprises: A fastening device having a motor that rotates a socket to which a workpiece can be attached, A torque measuring means for acquiring a fastening torque of the workpiece; An angle measuring means for acquiring a rotation angle of the workpiece is provided, The torque measuring means obtains the tightening torque for each predetermined angle obtained by the angle measuring means after the obtained tightening torque reaches a predetermined snug point, a difference calculation means for sequentially calculating a difference between the plurality of tightening torques obtained by the torque measurement means for each predetermined angle obtained by the angle measurement means; a difference monitoring means for monitoring the difference successively calculated by the previous difference calculation means, and issuing a command to stop the motor when it is determined that the difference satisfies a predetermined condition; a motor control means for stopping the motor upon receiving the stop command from the difference monitoring means; Contains:

[0009] The difference calculation means may be configured to calculate a moving average value of the acquired fastening torque as the difference.

[0010] The predetermined condition for the difference monitoring means may be that the difference is within a predetermined threshold for a predetermined period of time.

[0011] The fastening method of the present invention comprises the steps of: a torque acquisition step of acquiring a fastening torque of the workpiece at predetermined time intervals; a difference calculation step of sequentially calculating differences between the plurality of acquired fastening torques for the fastening torque; a stop step of stopping the fastening of the workpiece when it is determined that the sequentially calculated difference satisfies a predetermined condition; Contains:

[0012] The tightening method of the present invention further comprises the steps of: A torque acquisition step for acquiring the fastening torque of the workpiece; an angle acquisition step of acquiring a rotation angle of the workpiece at predetermined time intervals when the fastening torque reaches a predetermined snug point; a difference calculation step of acquiring the tightening torque for each predetermined angle acquired in the angle acquisition step, and sequentially calculating the difference between the acquired tightening torques; a stop step of stopping the tightening when it is determined that the sequentially calculated difference satisfies a predetermined condition; Contains:

[0013] The difference calculation step may be configured to calculate a moving average value of the acquired fastening torque as the difference.

[0014] The predetermined condition for the stopping step may be that the difference is within a predetermined threshold for a predetermined time. Effect of the Invention

[0015] According to the tightening device of the present invention, the difference in the tightening torque is calculated for each predetermined time or each predetermined rotation angle of the work while tightening the work, and if the difference remains within a predetermined threshold for a predetermined time before reaching the control torque or control rotation angle, tightening is stopped. This makes it possible to prevent the tightening torque from acting on the work and the axial force from increasing and causing the work to break when there is an abnormality in the work, such as a decrease in the torque coefficient value. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a block diagram of a fastening device according to the present invention. [Diagram 2] FIG. 2 is a control flowchart. [Diagram 3] FIG. 3 is a graph showing the change over time in the tightening torque and the difference therebetween. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a fastening device 10 and a fastening method thereof according to one embodiment of the present invention will be described with reference to the drawings.

[0018] FIG. 1 is a block diagram of a fastening device 10 according to an embodiment of the present invention, and FIG. 2 is a control flowchart.

[0019] The fastening device 10 is an electric tool having a socket 20 on the tip of a casing 11 to which a bolt, a screw, or the like is attached. The fastening device 10 includes a motor 12 for rotating the socket 20 inside the casing 11, and the socket 20 can be detachably attached to a rotating shaft connected to the motor 12 via a reduction mechanism (not shown). For example, the reduction mechanism can be a planetary gear mechanism, and the rotating shaft can be a two-shaft drive shaft consisting of an inner shaft and an outer shaft that can rotate in opposite directions. In this case, a torque acquisition step can be performed in which the socket 20 is attached to the inner shaft and the reaction force receiver 21 is attached to the outer shaft. Of course, the present invention can also be applied to a single-shaft fastening device.

[0020] The motor 12 of the tightening device 10 is connected to a power source such as a commercial power source or a battery via a control device 40. The motor 12 is driven by the operation of a forward / reverse changeover switch 14 for switching between forward and reverse rotation, and an on / off switch 13 such as a trigger switch. Note that the switches 13 and 14 are shown in the figure only as configurations.

[0021] The tightening device 10 also detects the tightening torque acting on the workpiece. For example, torque detection can be performed by a torque sensor 30, such as a strain gauge, provided on the inner or outer shaft, and a torque measuring means 31 that detects torque as a change in current, voltage, resistance, etc. of the torque sensor 30. The torque measuring means 31 can be provided in the control device 40 described above. Note that the torque measuring means 31 may be configured to detect the tightening torque from an electrical system in the control device 40, for example, a change in current supplied to the motor 12, etc.

[0022] The control device 40 is disposed at an appropriate position within the casing 11. In Fig. 1, the control device 40 shows only the main components necessary for the control of the present invention. The control device 40 has a control unit 41 composed of a CPU, memory, etc., and controls the fastening device 10 by executing various programs stored in the memory. Note that, in Fig. 1, representative functions realized by linking these are illustrated as functional blocks, but these functional blocks can be realized by hardware only, software only, or a combination of both.

[0023] For example, the control device 40 has a motor control means 42 for the motor 12, and controls the driving and stopping of the motor 12 by the switch 13, or the stopping of the motor 12 under a predetermined condition. As an example, in the control of the fastening device 10, as shown in the flowchart in Fig. 2, the motor 12 is driven by the operation of the switch 13 (step S1) to start fastening (step S2). Then, the fastening torque is measured by the torque sensor 30 or the torque measurement means 31 (step S3: torque acquisition step), and the driving of the motor 12 is continued until the fastening torque reaches a preset control torque. When the fastening torque reaches the control torque (YES in step S3), the motor control means 42 stops the driving of the motor 12 (step S4).

[0024] In the fastening device 10 and fastening method of the present invention, in addition to the above general control, the fastening torque of the workpiece detected by the torque sensor 30 or torque measuring means 31 is referenced, and the difference in the obtained fastening torque is monitored to check whether the workpiece is being fastened normally, or if there is an abnormality in the workpiece such as a decrease in the torque coefficient value, the fastening is stopped before the workpiece is twisted off (steps S3 to S11).

[0025] As a specific embodiment for realizing the above function, the torque measuring means 31 measures the fastening torque at predetermined time intervals, for example, every 10 msec (step S3: torque acquisition step). The measured fastening torque can be recorded in the memory of the control unit 41 and can also be used as fastening torque data for each workpiece.

[0026] The difference calculation means 43 acquires the obtained fastening torque (step S5). The difference calculation means 43 sequentially receives the fastening torques from the torque measurement means 31, or sequentially acquires the fastening torques stored in the memory. The difference calculation means 43 then appropriately calculates the difference from the multiple obtained fastening torques (step S5: difference calculation step). For example, the difference calculation means 43 calculates the difference between chronologically adjacent fastening torques, the difference between fastening torques separated by a predetermined time or a predetermined section, or the moving average value of the fastening torques included in a predetermined time or a predetermined section. The calculated difference is sent to the difference monitoring means 44 described below, or stored in the memory.

[0027] For example, the calculation formula for the difference between the moving average values ​​in a predetermined interval performed by the difference calculation means 43 is shown in the following formula 1. In formula 1, the interval M can be set to 10, for example.

[0028]

number

[0029] Then, the difference calculated by the difference calculation means 43 is acquired by the difference monitoring means 44 (step S6). The difference monitoring means 44 judges whether or not the obtained multiple differences satisfy a predetermined condition, and if the predetermined condition is satisfied (YES in steps S6 to S9 described below), it judges that there is an abnormality in the fastening, and transmits a command to stop the motor 12 to the motor control means 42 (step S10: stop step).

[0030] When the difference monitoring means 44 judges that the difference does not satisfy the predetermined condition (step S6 NO ), this is normal tightening and the tightening torque gradually increases, so the motor control means 42 continues to drive the motor 12 until the tightening torque reaches the control torque (YES in step S3, step S4). The tightening torque of the workpiece during normal tightening and the difference therebetween are shown in "Invention example (normal): tightening torque" and "Invention example (normal): difference" in Figure 3. Details of Figure 3 will be described later.

[0031] The above-mentioned predetermined condition may be, for example, that the difference calculated by the difference calculation means 43 is within a predetermined threshold (for example, ±3 Nm) for a predetermined time (for example, 3 seconds). Specifically, the difference calculation means 43 includes a monitoring timer, and when the calculated difference falls within the predetermined threshold (YES in step S6), the monitoring timer is started, or if the monitoring timer has already been started, the timer is counted up (step S7). When the state within the predetermined threshold continues for a predetermined time (for example, 3 seconds), it is determined that there is an abnormality in the fastening (YES in step S9). The cause of the abnormality may be, for example, a decrease in the torque coefficient value of the workpiece. In this case, the difference monitoring means 44 sends a stop command for the motor 12 to the motor control means 42 (step S10: stop step), and the motor 12 is stopped due to an abnormality. The fastening torque of the workpiece during abnormal fastening and the difference therebetween are shown in "Invention example (abnormal): fastening torque" and "Invention example (abnormal): difference" in FIG. 3. Details will be described later.

[0032] When the motor 12 is stopped abnormally by a stop command of the difference calculation means 43 (step S10), the workpiece has not been tightened by the control torque, so it is desirable for the control device 40 to notify the worker of the abnormal stop. For example, in the case of an abnormal stop, the motor 12 cannot be driven even if the switch 13 is operated again, and it is desirable to require a reset operation, such as disconnecting the commercial power supply or operating a specified switch (step S11).

[0033] As described above, by monitoring the tightening torque and the difference between them, tightening abnormalities can be detected early. If an abnormality is detected, the motor 12 is immediately stopped to prevent the workpiece from being unscrewed, and measures such as removing the workpiece can be taken early.

[0034] A workpiece was actually fastened using the fastening device 10 and fastening method of the present invention. In the examples, there were an example of the invention (normal) in which the workpiece was normally fastened using the fastening device 10 of the present invention, an example of the invention (abnormal) in which an abnormality occurred in the fastening of the workpiece, and, for comparison, a comparative example (abnormal) in which the difference was not calculated and fastening was continued for a workpiece with a fastening abnormality.

[0035] The actual tightening torque values ​​measured for the example (normal), example (abnormal), and comparative example (abnormal) as well as the difference between them were measured and calculated, and these were visualized as a graph (Figure 3) with the vertical axis representing time (seconds) and the horizontal axis representing time.

[0036] 3, in the example of the invention (normal), the tightening torque reaches the control torque (800 Nm ±10%) about 2.3 seconds after tightening starts, and tightening is completed. At this time, the tightening torque difference reaches the predetermined threshold value (±3 Nm) just before tightening is completed, but it can be seen that tightening is completed about 0.3 seconds before the predetermined time count (3 seconds) by the monitoring timer has elapsed.

[0037] In the example of the invention (abnormal), after the tightening starts, the tightening progresses slowly, and the difference in the tightening torque itself becomes within the threshold (±3 Nm) in about 1.8 seconds, and as shown in the figure, the timer to monitor thread breakage is activated. The difference then decreases slightly while remaining within the threshold, and after 3 seconds, the motor 12 stops (abnormal stop) due to the passage of a predetermined time. This makes it possible to stop tightening the work before the thread breaks. Also, because the motor 12 stops before the thread breaks, measures such as removing the work can be taken early.

[0038] On the other hand, in the comparative example (abnormal), after the start of tightening, tightening proceeded slowly, the tightening torque stopped increasing in about 3 to 5 seconds, and tightening continued like this for about 5 seconds (actual measurement: up to about 10 seconds), after which the workpiece was unscrewed (broken). If the abnormality is detected after the workpiece is unscrewed, not only will it take time to detect, but it will also be time-consuming to remove the workpiece, significantly reducing work efficiency.

[0039] In the above, the difference in fastening torque is detected at predetermined time intervals to stop the motor 12 before the workpiece breaks. However, it is also possible to obtain the rotation angle of the workpiece, rotating shaft, motor, etc. after reaching the snug point and monitor the difference in fastening torque for each rotation angle to detect abnormalities in the workpiece.

[0040] In this case, the torque measuring means 31 is a mechanism capable of detecting a snag point, and in addition to the torque measuring means 31, the rotation angle of the workpiece or the like is detected by an angle measuring means such as an angle sensor (angle acquisition step). After the torque measuring means 31 detects the snug point, the torque measuring means 31 acquires the fastening torque for each predetermined angle detected by the angle measuring means, and the difference in the fastening torque obtained is acquired by the difference calculating means 43 to sequentially calculate the difference in the fastening torque (difference calculation step), and the difference is monitored by the difference monitoring means 44. If the difference in the fastening torque monitored by the difference monitoring means 44 satisfies a predetermined condition, for example, within a predetermined threshold for a predetermined time, before the rotation angle reaches a predetermined control rotation angle, it is determined that an abnormality has occurred in the fastening of the workpiece, and the motor 12 is stopped due to an abnormality.

[0041] In this case, the fastening torque, the workpiece rotation angle, and the difference in fastening torque for each predetermined angle can be expressed as a T-θ curve with the horizontal axis representing angle in the graph shown in Figure 3. If the horizontal axis represents time, the rotation angle of the motor 12 becomes a disturbance to the torque gradient, and the rotation speed is affected by the applied voltage of the motor 12 and the level of the fastening torque. However, since the workpiece rotation angle is not affected by these factors, by calculating and monitoring the difference in fastening torque with respect to the workpiece rotation angle, the accuracy of preventing thread breakage can be significantly improved compared to monitoring the difference in fastening torque with respect to time.

[0042] The above description is for the purpose of explaining the present invention, and should not be interpreted as limiting the invention described in the claims or restricting the scope of the invention. Furthermore, the configuration of each part of the present invention is not limited to the above embodiment, and various modifications are possible within the technical scope described in the claims.

[0043] For example, the configuration of the fastening device 10 is not limited to the above embodiment. Also, it should be understood that the above-mentioned fastening torque values ​​and times are merely examples and can be modified in various ways. [Explanation of symbols]

[0044] 10 Fastening device 12 Motor 20 Sockets 30 Torque Sensor 31 Torque measuring means 40 Control device 42 Motor control means 43 Difference calculation means 44 Differential monitoring means

Claims

1. A fastening device having a motor that rotates a socket to which a workpiece can be attached, a torque measuring means for acquiring the fastening torque of the workpiece at predetermined time intervals; A difference calculation means for sequentially calculating a difference between the plurality of tightening torques acquired by the torque measurement means; a difference monitoring means for monitoring the difference successively calculated by the difference calculation means, and issuing a command to stop the motor when it is determined that the difference satisfies a predetermined condition; a motor control means for stopping the motor upon receiving the stop command from the difference monitoring means; Contains The predetermined condition is that a state in which the difference is within a predetermined threshold range continues for a predetermined time while the motor is driven, and the predetermined time is a time that is longer than a time during which the difference calculated while the motor is driven during normal fastening remains within the predetermined threshold range and is shorter than a time until the workpiece breaks. Fastening device.

2. The difference calculation means calculates a moving average value of the acquired tightening torque as the difference. The fastening device of claim 1.

3. A method for fastening a workpiece using a fastening device having a motor that rotates a socket to which the workpiece can be attached, comprising: a torque acquisition step of acquiring a fastening torque of the workpiece at predetermined time intervals; a difference calculation step of sequentially calculating differences between the plurality of acquired fastening torques for the fastening torque; a stop step of stopping the fastening of the workpiece when it is determined that the sequentially calculated difference satisfies a predetermined condition; Contains The predetermined condition is that a state in which the difference is within a predetermined threshold range continues for a predetermined time while the motor is driven, and the predetermined time is a time that is longer than a time during which the difference calculated while the motor is driven during normal fastening remains within the predetermined threshold range and is shorter than a time until the workpiece breaks. Fastening method.

4. The difference calculation step calculates a moving average value of the acquired fastening torque as the difference. The fastening method according to claim 3.

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