Cam-out detection system, bit wear detection system, and computer program

Abstract

To assist abrasion of a bit to more easily let a user know.SOLUTION: A controller 4 for detecting coming out of a bit mounted on an output shaft of a screw fastening device is provided with: a torque rate calculation part 401 for acquiring fastening torque in a fastening period during which the output shaft fastens a screw as an object to be fastened through a bit, and its torque rate on the basis of a torque detection signal 61 and an angle detection signal 62; and a coming out discrimination part 404 for discriminating that coming out occurs, when the torque rate exceeds a second rate threshold of 0 or more and there is no timing when the fastening torque is equal to or more a torque threshold, in a monitoring period until the output shaft rotates at a predetermined angle after the torque rate becomes equal to or less than a first rate threshold of 0 or less.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to detection of the state of a bit of a screw tightening device.

Background Art

[0002] A screw tightening device is used for tightening screws of workpieces on a factory production line. The screw tightening device is provided with bits having various tip shapes, and a bit corresponding to the screw standard is selectively mounted.

[0003] The bit gradually wears at the tip due to friction with the screw head. When the wear progresses considerably, the fitting between the bit and the screw becomes loose, and the tip of the bit is likely to separate from the screw head and escape outside the screw head. That is, cam-out is likely to occur on the screw head.

[0004] Therefore, when a bit with considerably advanced wear is used, tightening failure or a temporary stop of the production line due to bit replacement (so-called choco stop) is likely to occur, which causes deterioration of production efficiency.

[0005] In addition, cam-out may damage the hole of the screw head, which may cause a decrease in the function of the screw and prevent proper tightening.

[0006] Furthermore, when cam-out occurs, the screw head may be shaved and become metal powder. The metal powder causes so-called contamination problems in electrical mounting parts and precision instruments. For example, the metal powder may cause a short circuit in an electronic circuit. In particular, as the circuit integration rate improves year by year, the influence of the metal powder becomes greater. Or it may damage the product.

[0007] Therefore, technologies have been proposed to suppress the occurrence of cam-out. The control device described in Patent Document 1 includes a storage means for storing data relating to the tightening torque pattern and the corresponding pressing force pattern, a tightening torque detection means, a means for detecting the occurrence of cam-out of the driver bit when a torque fluctuation larger than a predetermined value is detected by monitoring the tightening torque, a means for storing the tightening torque pattern at that time, and a means for correcting the pressing force near the cam-out occurrence position to a value larger than the reference pressing force, and then storing it as the corrected pressing force pattern. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 6-304827 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, completely preventing cam-out is difficult. Therefore, to reduce short stoppages and contamination, it is important to inform the user in advance about bit wear.

[0010] In view of these problems, the present invention aims to help users be more easily notified of bit wear than before. [Means for solving the problem]

[0011] A cam-out detection system according to one embodiment of the present invention is a cam-out detection system for detecting cam-out of a bit mounted on the output shaft of a screw tightening device, comprising: a torque acquisition means for acquiring the tightening torque during a tightening period in which the output shaft tightens a screw to be tightened via the bit; a torque rate acquisition means for acquiring the torque rate of the tightening torque during the tightening period; and a cam-out determination means for determining that cam-out has occurred if, during a monitoring period from when the torque rate falls below a first rate threshold of 0 or less until the output shaft rotates by a predetermined angle, there is no timing in which the torque rate exceeds a second rate threshold of 0 or more and the tightening torque is equal to or greater than the torque threshold.

[0012] Preferably, the system includes a suspected cam-out detection means that detects suspected cam-out when the torque rate falls below the first rate threshold, and the cam-out determination means starts monitoring the tightening torque and torque rate when suspected cam-out is detected by the suspected cam-out detection means, determines that cam-out has occurred if there is no timing during the monitoring period and terminates the monitoring, terminates the monitoring if there is timing during the monitoring period, and the suspected cam-out detection means stops detecting suspected cam-out while the tightening torque and torque rate are being monitored by the cam-out determination means. [Effects of the Invention]

[0013] According to the present invention, bit cam-out can be detected more easily than in the conventional method. This makes it easier to inform the user of bit wear than in the conventional method. [Brief explanation of the drawing]

[0014] [Figure 1] This figure shows an example of the overall configuration of a screw fastening system. [Figure 2] This diagram shows examples of the hardware configurations for the screw tightening device and the personal computer. [Figure 3]This diagram shows examples of the functional configurations of the controller and the personal computer. [Figure 4] This figure shows examples of the transitions between tightening torque and torque rate. [Figure 5] This flowchart illustrates an example of the overall processing flow by the controller and personal computer. [Modes for carrying out the invention]

[0015] [Overall structure] Figure 1 shows an example of the overall configuration of the screw tightening system 1. Figure 2 shows an example of the hardware configuration of the screw tightening device body 3 and the personal computer 5.

[0016] The screw tightening system 1 shown in Figure 1 consists of a screw tightening device 2 and a personal computer 5, and performs screw tightening on a workpiece. For example, a Phillips screw 291 is tightened into a predetermined part 28a of a product 28.

[0017] The screw tightening device 2 tightens and loosens screws such as Phillips screws, Torx screws, nuts, or bolts. Devices primarily used for automatically tightening and loosening screws are sometimes commonly called "nut runners" or "automatic fasteners." "Torx" is a registered trademark.

[0018] The screw tightening device 2 consists of a screw tightening device body 3 and a controller 4. A set of multiple bits 39 (391, 392, 393, ...) with different tip shapes and sizes is also provided. These bits 39 are detachable and are used selectively depending on the size and shape of the screw head being tightened. For example, when tightening a Phillips screw 291, bit 391 is attached to the screw tightening device body 3 and used.

[0019] As shown in FIG. 2, the screw tightening device main body 3 is composed of a motor 31, a reduction gear 32, an output shaft 33, a torque sensor 34, an angle sensor 35, and the like.

[0020] The motor 31 is a rotational drive source that rotates the output shaft 33 via the reduction gear 32 by the current supplied from the controller 4.

[0021] At the tip of the output shaft 33, a bit 39 corresponding to the tightening target among the plurality of bits 39 is attached. A screw is fitted into the bit 39, and the output shaft 33 rotates together with the bit 39 by the motor 31 to rotate the screw. In the example of FIG. 1, the bit 391 corresponding to the plus screw 291 is attached, and the plus screw 291 rotates.

[0022] During the operation of the motor 31, the torque sensor 34 constantly detects the tightening torque TQ of the screw by the motor 31, and transmits a torque detection signal 61 indicating the detected tightening torque TQ to the controller 4. In the present embodiment, among the torques output by the motor 31, the torque generated on the output shaft 33, that is, the torque for tightening the screw which is the load, is directly detected as the tightening torque TQ.

[0023] During the operation of the motor 31, the angle sensor 35 constantly detects the rotation angle θ by which the output shaft 33 has rotated, and transmits an angle detection signal 62 indicating the detected rotation angle θ to the controller 4. The torque detection signal 61 and the angle detection signal 62 are transmitted to the controller 4 synchronously. Or they are synchronized in the controller 4.

[0024] Returning to FIG. 1, the controller 4 is a device that supplies current to the screw tightening device main body 3 and controls the screw tightening device main body 3 based on data given from the personal computer 5 or feedback from the screw tightening device main body 3, etc. Further, it discriminates cam-out based on the torque detection signal 61 and the angle detection signal 62, and notifies the personal computer 5. The method for discriminating cam-out will be described later.

[0025] The personal computer 5 is a device that allows the user to provide setting values ​​to the screw tightening device body 3 to the controller 4 and to check the current or past state of the screw tightening device body 3. In this embodiment, it is also used to detect wear on the bit 39 and notify the user.

[0026] As shown in Figure 2, the personal computer 5 consists of a main arithmetic unit 51, main memory 52, auxiliary storage device 53, input / output interface 54, display 55, keyboard 56, and pointing device 57, among others.

[0027] Main memory 52 is the main RAM (Random Access Memory) of the personal computer 5. Auxiliary storage device 53 contains the operating system, setting programs for various values, and computer programs such as a bit wear detection program 50. The bit wear detection program 50 is a program for detecting and notifying of bit wear 39. These computer programs are loaded into RAM 52 as needed.

[0028] The main processing unit 51 is a processor such as a CPU (Central Processing Unit) that executes computer programs loaded into the main memory 52.

[0029] The input / output interface 54 is a communication board conforming to the same specifications as the input / output interface of the controller 4, and communicates with the controller 4. The display 55 displays various screens, which will be described later. The keyboard 56 and pointing device 57 are used by the user to input settings and commands.

[0030] [Wear detection process] Figure 3 shows examples of the functional configurations of the controller 4 and the personal computer 5. Figure 4 shows examples of the transitions between the tightening torque TQ and the torque rate TR.

[0031] Next, we will explain the process by which the controller 4 and the personal computer 5 detect wear on bit 39.

[0032] According to the bit wear detection program 50, functions such as the counting unit 501, wear detection unit 502, wear notification unit 503, and tightening completion notification unit 504 shown in Figure 3 are implemented in the personal computer 5. The controller 4 also has functions such as a torque rate calculation unit 401, a seating detection unit 402, a suspected cam-out detection unit 403, a cam-out discrimination unit 404, and a tightening completion detection unit 405. These functions may be implemented by a program or by a circuit. The processing by each unit shown in Figure 3 will be explained below, along with the operation of the screw tightening device body 3, using the case of tightening a Phillips screw 291 (see Figure 1) to part 28a of product 28 as an example.

[0033] In the screw tightening device body 3, a bit 39, or bit 391, corresponding to the Phillips screw 291, is mounted on the output shaft 33 (see Figure 1). When the Phillips screw 291 is fitted into the bit 391 and a command to start tightening is input, the motor 31 (see Figure 2) rotates the output shaft 33 at high speed and performs preliminary tightening until the Phillips screw 291 is seated. After seating, final tightening begins. Tightening in impact mode corresponds to final tightening. The output of the output shaft 33 may be temporarily suspended when switching from preliminary tightening to final tightening.

[0034] As described above, the controller 4 receives the torque detection signal 61 and the angle detection signal 62.

[0035] The torque rate calculation unit 401 calculates the tightening torque TQ for each rotation angle θ based on the torque detection signal 61 and the angle detection signal 62, and further calculates the torque rate TR as the ratio of the increment ΔTQ of the tightening torque TQ to the increment Δθ of the rotation angle θ. The following explanation will use the case where F(θ) and G(θ) shown in Figure 4 are calculated as the tightening torque TQ and torque rate TR for each rotation angle θ as an example.

[0036] The seating detection unit 402 detects that the Phillips screw 291 has seated and that preliminary tightening is complete when the tightening torque TQ reaches the seating torque TQs. In the example in Figure 4, seating is detected at a rotation angle θ1. The seating torque TQs is preset for each bit 39. Therefore, in this example, the seating torque TQs of bit 391 is used.

[0037] The suspected cam-out detection unit 403 monitors the torque rate TR after the seating detection unit 402 detects that the Phillips screw 291 has seated. If the torque rate TR falls below the trigger torque rate TRg, the unit detects a suspected cam-out. In other words, it determines that there is a suspicion of cam-out. In the example in Figure 4, suspected cam-out is detected at rotation angle θ2 and rotation angle θ4. The trigger torque rate TRg may be zero, but it is preferable to have a negative value to reduce false detections. In the latter case, the trigger torque rate TRg is experimentally determined and set for each bit 39. In this example, the trigger torque rate TRg of bit 391 is used.

[0038] However, during the period when the cam-out determination unit 404 is monitoring whether the non-cam-out confirmation conditions described later are met (hereinafter referred to as the "monitoring period"), the suspected cam-out detection unit 403 stops monitoring the torque rate TR. In other words, during the monitoring period, even if the torque rate TR falls below the trigger torque rate TRg, it is ignored. Then, once the determination by the cam-out determination unit 404 is complete, monitoring of the torque rate TR is resumed.

[0039] When a suspected camout is detected by the suspected camout detection unit 403, the camout determination unit 404 determines whether the cause of the detected suspected camout, i.e., the reason why the torque rate TR fell below the trigger torque rate TRg (hereinafter referred to as the "suspected camout cause"), is the camout of bit 391, as follows:

[0040] The cam-out determination unit 404 monitors whether the non-cam-out confirmation conditions are met to determine whether the suspected cam-out cause is the cam-out of bit 391.

[0041] The condition for confirming non-cam-out is that the tightening torque TQ exceeds the monitored effective torque TQy as the tightening torque TQ increases. In other words, the conditions TR>0 and TQ>TQy are both satisfied simultaneously. The monitored effective torque TQy is preset for each bit 39, and in this example, the monitored effective torque TQy of bit 391 is used. Furthermore, it is desirable that the monitored effective torque TQy is a value that allows us to estimate that the final tightening has been successfully resumed. Therefore, it is set to the same value as the seating torque TQs or a value around it. Note that in order to reduce false detections, TR>TRy may be used instead of TR>0. TRy is a positive value detected during final tightening and can be set arbitrarily.

[0042] Monitoring to determine whether the non-cam-out confirmation conditions are met begins from the moment a suspected cam-out is detected and, in principle, continues until the output shaft 33 has rotated by the monitoring interval angle θw from that point. The monitoring interval angle θw is determined and set experimentally in advance for each bit 39. Alternatively, it is determined and set experimentally in advance for each combination of bit 39 and the screw to be fastened. It may also be determined and set experimentally in advance taking into account other environmental factors (e.g., rotational speed). In this example, the monitoring interval angle θw corresponding to bit 391 is used. When using bit 39 for Phillips screws, i.e., a cross bit (Phillips bit), the monitoring interval angle θw is set to 45 degrees. However, as mentioned above, it may be set to an angle greater than or less than 45 degrees depending on other conditions such as the object to be fastened. The significance of the monitoring interval angle θw will be explained later.

[0043] If the output shaft 33 rotates by the monitoring interval angle θw without satisfying the non-cam-out confirmation condition, the cam-out determination unit 404 determines that the suspected cam-out cause is cam-out, as indicated by bit 391. Then, it terminates monitoring.

[0044] In the example in Figure 4, after a suspected cam-out is detected at rotation angle θ2, the output shaft 33 rotates by the monitoring interval angle θw without a timing occurring where both TR>0 and TQ>TQy are satisfied. Therefore, the cam-out determination unit 404 does not detect that the non-cam-out confirmation condition is met during the monitoring period, and determines that the cause of this suspected cam-out is the cam-out of bit 391.

[0045] On the other hand, if the cam-out determination condition is found to be met before the output shaft 33 rotates by the monitoring interval angle θw, the cam-out determination unit 404 determines that the suspected cam-out cause is not the cam-out of bit 391 and terminates monitoring. Then, the suspected cam-out monitoring is restarted by the suspected cam-out detection unit 403.

[0046] For example, the period immediately before rotation angle θ4 is not a monitoring period. At rotation angle θ4, the torque rate TR becomes less than or equal to the trigger torque rate TRg. Therefore, the suspected cam-out detection unit 403 detects suspected cam-out at rotation angle θ4.

[0047] The cam-out determination unit 404 then begins monitoring whether the non-cam-out confirmation condition is met. At rotation angle θ5, that is, before the output shaft 33 has finished rotating by the monitoring interval angle θw from rotation angle θ4, the non-cam-out confirmation condition is met. Therefore, the cam-out determination unit 404 determines that the suspected cause of cam-out in this case is not cam-out (bit 391) and terminates monitoring.

[0048] Thus, when the cam-out detection unit 404 detects a suspected cam-out, it monitors the tightening torque TQ and torque rate TR for the monitoring period immediately following the detection to detect the cam-out of bit 391. The principle is as follows.

[0049] When the torque rate TR falls below the trigger torque rate TRg, if the cause (suspected cam-out cause) is not a cam-out, the non-cam-out confirmation condition is immediately met. The non-cam-out confirmation condition is that the tightening torque TQ exceeds the monitored effective torque TQy, and the torque rate TR is positive, both of which are met simultaneously. In other words, for example, when the friction generated on the output shaft 33 changes from static friction to dynamic friction, the torque rate TR may momentarily fall below the trigger torque rate TRg (i.e., less than zero), but the tightening torque TQ immediately rises and the non-cam-out confirmation condition is met. The rotation angle of the output shaft 33 during the period from the detection of the suspected cam-out cause to the meeting of the non-cam-out confirmation condition (hereinafter referred to as the "non-cam-out rotation angle") is small, for example, (θ5-θ4).

[0050] On the other hand, if the cause is cam-out, the output shaft 33 rotates more than in the case of non-cam-out during the period from when the torque rate TR becomes less than or equal to the trigger torque rate TRg until the bit 391 re-engages with the Phillips screw 291 and the non-cam-out condition is met. The rotation angle of the output shaft 33 during this period (hereinafter referred to as the "cam-out rotation angle") is sufficiently larger than the non-cam-out rotation angle.

[0051] In light of the above properties, in this embodiment, the cam-out rotation angle is experimentally determined in advance and set as the monitoring interval angle θw. Alternatively, an angle slightly smaller than the cam-out rotation angle (for example, an angle obtained by subtracting a predetermined value) is set as the monitoring interval angle θw. However, an angle larger than the non-cam-out rotation angle is set. The non-cam-out rotation is also determined experimentally. The cam-out determination unit 404 then determines that the cause of suspected cam-out is cam-out if the non-cam-out determination condition is not met for at least the period until the output shaft 33 has rotated by the monitoring interval angle θw (i.e., the monitoring period), and determines that it is not cam-out if the condition is met.

[0052] When the cam-out detection unit 404 determines that the cause of the suspected cam-out is a cam-out, it notifies the personal computer 5 of the cam-out.

[0053] In the personal computer 5, the counting unit 501 is equipped with counters CT (CT1, CT2, CT3, ...) for each of the 39 bits (391, 392, 393, ...). Whenever a cam-out is detected by the cam-out detection unit 404 of the controller 4, the counter CT of bit 39 attached to the screw tightening device body 3 is incremented. That is, "1" is added. In this example, bit 391 is attached, so each time a cam-out is detected, counter CT1 is incremented. In the example in Figure 4, the counter is incremented once at a rotation angle θ3.

[0054] The counting unit 501 only needs to recognize which bit 39 is attached to the output shaft 33 by having the user input it in advance (for example, at the time of attachment).

[0055] The wear detection unit 502 detects that the wear of bit 39 having counter CT has reached a considerable degree if the value of the counted-up counter CT is equal to or greater than the wear threshold α. Hereinafter, this considerable degree of wear will be referred to as "permissible limit wear". In this example, if the value of counter CT1 is equal to or greater than the wear threshold α, the permissible limit wear of bit 391 is detected.

[0056] The wear notification unit 503 notifies the wear detection unit 502 of the wear limit wear of the bit 39 when the wear detection unit 502 detects that the wear limit wear has been reached. For example, it notifies the wear by displaying text such as "The bit currently in use is worn out. Please replace it with a new bit." on the display 55 (see Figure 2) as the wear message 65.

[0057] In the controller 4, the tightening completion detection unit 405 detects that tightening is complete when the tightening torque TQ reaches the target torque TQp, and notifies the personal computer 5 of the completion of tightening.

[0058] In the personal computer 5, if the tightening completion notification unit 504 receives notification from the controller 4 that tightening is complete without the wear detection unit 502 detecting the permissible limit wear, it will notify the controller 4 of a message 66 indicating that bit 391 is good. Alternatively, if the tightening completion is notified without the counter CT1 being counted up, it may notify the controller 4 of a message 67 indicating that no cam-out occurred. Messages 66 and 67 may be notified by the controller 4.

[0059] In addition, the cam-out detection unit 404 may detect multiple cam-outs during a single tightening operation. In such cases, it can be estimated that wear has reached a considerable degree without processing by the personal computer 5. Therefore, if the cam-out detection unit 404 detects a predetermined number of cam-outs (for example, 2 or more) during a single tightening operation, it can be estimated that wear has reached a considerable degree at that point, and a wear message 65 may be output. Alternatively, multiple cam-outs may be detected due to malfunctions other than wear, such as a malfunction in the positional relationship between the bit 391 and the Phillips screw 291. Therefore, an error message may be output if a predetermined number of cam-outs are detected during a single tightening operation.

[0060] Figure 5 is a flowchart illustrating an example of the overall processing flow by the controller 4 and the personal computer 5.

[0061] Next, the overall process flow for detecting the permissible limit wear of bit 39 by the controller 4 and personal computer 5 will be explained with reference to a flowchart, using the case where bit 391 is used as an example.

[0062] When the tightening of bit 391 is started by the screw tightening device body 3, the controller 4 receives a torque detection signal 61 and an angle detection signal 62 sequentially, and begins calculating the tightening torque TQ and torque rate TR for each rotation angle θ (Figure 5, #101).

[0063] Controller 4 monitors the seating of bit 391 by monitoring whether the tightening torque TQ has reached the seating torque TQs (#102). When seating of bit 391 is detected (Yes in #103), it monitors for the occurrence of suspected cam-out by monitoring whether the torque rate TR is less than or equal to the trigger torque rate TRg (#104). If the tightening torque TQ reaches the target torque TQp without detecting suspected cam-out (Yes in #105), the bit wear detection program 50 terminates its processing.

[0064] If suspected cam-out is detected before the tightening torque TQ reaches the target torque TQp (No in #105, Yes in #106), the controller 4 monitors whether the non-cam-out condition is met during the period from the time of detection until the output shaft 33 rotates by the monitoring interval angle θw, i.e., during the monitoring period (No in #107) (#108). In other words, it monitors whether both TR>0 and TQ>TQy are met simultaneously. If it detects that the non-cam-out condition is met (Yes in #109), it determines that the cause of the suspected cam-out in this case is not cam-out (#110).

[0065] On the other hand, if the monitoring period expires without detecting that the non-cam-out confirmation conditions are met (No in #109), controller 4 determines that the suspected cause of the cam-out is indeed a cam-out (#111). In other words, it detects a cam-out.

[0066] When controller 4 detects cam-out, personal computer 5 increments counter CT1, which is bit 391 (#112). Based on counter CT1, it determines whether or not there is wear at the permissible limit (#113), and if wear at the permissible limit is detected (Yes in #114), that is, if the value is greater than or equal to the wear threshold α, it broadcasts a wear message 65 (#115).

[0067] Until the tightening torque TQ reaches the target torque TQp (No in #116), the controller 4 performs the processes in steps #104 to #111 as appropriate, and the personal computer 5 performs the processes in steps #112 to #115 as appropriate. Then, when the target torque TQp is reached (Yes in #116), the series of processes for detecting bit wear ends.

[0068] According to this embodiment, it is possible to easily detect the cam-out of the bit 39 and to detect when the wear of the bit 39 has reached the permissible limit.

[0069] [Variations and application examples] In this embodiment, the controller 4 detects suspected cam-out when the torque rate TR falls below the trigger torque rate TRg, but it may also detect suspected cam-out when the tightening torque TQ falls below a predetermined value. Alternatively, it may detect suspected cam-out when the tightening torque TQ decreases by a predetermined amount. Furthermore, if the tightening torque TQ reaches the effective monitoring torque TQy during the monitoring period, it may be determined that the cause of the suspected cam-out is not cam-out, and if it does not reach that level, it may be determined that it is cam-out.

[0070] In this embodiment, the conditions TR>0 and TQ>TQy were used as the non-cam-out determination conditions, but conditions relating only the tightening torque TQ may also be used. For example, only TQ>TQy may be used as the non-cam-out determination condition.

[0071] In this embodiment, the controller 4 performs the determination of whether the suspected cam-out is actually a cam-out (i.e., cam-out detection), and the personal computer 5 performs wear detection based on the number of cam-outs. However, a single device may perform both functions. For example, the controller 4 may perform both functions.

[0072] In this embodiment, the personal computer 5 determines whether or not bit 39 has reached its permissible limit of wear, but it may also detect the progress of wear on bit 39. For example, as a measure of the progress of wear, if the value of counter CT is less than the threshold α1, "wear level 1" may be detected; if the value is between α1 and α2, "wear level 2" may be detected; if the value is between α2 and α3, "wear level 3" may be detected; and if the value is α3 or greater, "wear level 4" may be detected. Note that α1 < α2 < α3 < α4.

[0073] In this embodiment, the presence or absence of wear at the permissible limit of bit 39 was determined based on the value of counter CT, i.e., the total number of cam-outs of bit 39. However, it may also be determined based on the frequency of cam-outs.

[0074] In this case, for example, the personal computer 5 records how many screw tightenings it took to detect each cam-out. Then, if cam-out occurs at a predetermined frequency, that is, in the most recent predetermined number of screw tightenings (for example, the most recent 100 screw tightenings), with a threshold value (for example, 3 times), it is detected that wear has reached a considerable degree. Note that the predetermined frequency can be set arbitrarily.

[0075] For each combination of workpiece and bit 39, the time until permissible wear limit is reached or the number of tightening cycles may be recorded. Alternatively, the number of bit 39 replacements per unit period or unit number of tightening cycles may be recorded. Based on this information, the timing of bit 39 replacement can be predicted without detecting cam-out, allowing for proactive replacement of the bit 39 and implementation of preventive maintenance.

[0076] The threshold values ​​used in the bit wear detection program 50, such as the seating torque TQs, the monitored effective torque TQy, the trigger torque rate TRg, and the monitored interval angle θw, may be set for each combination of workpiece and bit 39 and used accordingly.

[0077] In this embodiment, the controller 4 detects cam-out in parallel with the screw tightening by the screw tightening device body 3, that is, in near real-time, and the personal computer 5 performs processing using the bit wear detection program 50. However, the torque detection signal 61 and the angle detection signal 62 may be temporarily stored in storage, and the controller 4 and personal computer 5 may perform their respective processing after the screw tightening is completed.

[0078] In this embodiment, the counting unit 501, wear detection unit 502, wear notification unit 503, and tightening completion notification unit 504 are implemented by the personal computer 5, but they may also be implemented by a PCL (Programmable Logic Controller). Alternatively, each function of the controller 4 and each function of the personal computer 5 shown in Figure 3 may be executed by a single computer through a program, or they may be implemented by a single PCL.

[0079] In this embodiment, various setting values ​​such as the monitoring interval angle θw were experimentally determined in advance, but values ​​calculated by a simulator or the like may also be used.

[0080] Furthermore, the overall configuration or individual parts of the screw tightening system 1, screw tightening device 2, screw tightening device body 3, controller 4, and personal computer 5, as well as the content of processing and the sequence of processing, can be appropriately modified in accordance with the spirit of the present invention. [Explanation of Symbols]

[0081] 1. Screw tightening system (cam-out detection system) 3. Screw tightening device body 33 Output shaft 34 Torque sensor (torque acquisition means) 39 bit 4 controllers 5. Personal Computers 401 Torque rate calculation unit (torque rate acquisition means) 403 Suspected Cam-Out Detection Unit (Suspected Cam-Out Detection Means) 404 Cam-out detection unit (cam-out detection means) 502 Wear detection unit (wear discrimination means)

Claims

1. A cam-out detection system for detecting cam-out of a bit mounted on the output shaft of a screw tightening device, Torque acquisition means that acquires the tightening torque during the tightening period in which the output shaft tightens the screw to be tightened via the bit, Torque rate acquisition means for acquiring the torque rate of the tightening torque during the tightening period, A cam-out determination means determines that a cam-out has occurred if, during the monitoring period from when the torque rate falls below a first rate threshold of 0 or less until the output shaft rotates by a predetermined angle, there is no timing when the torque rate exceeds a second rate threshold of 0 or more and the tightening torque is equal to or greater than the torque threshold. A cam-out detection system characterized by having the following features.

2. A suspected cam-out detection means for detecting a suspected cam-out when the torque rate falls below the first rate threshold, It has, The cam-out determination means starts monitoring the tightening torque and torque rate when the suspected cam-out is detected by the suspected cam-out detection means, determines that the cam-out has occurred if the timing is not present during the monitoring period and terminates the monitoring, and terminates the monitoring if the timing is present during the monitoring period. The suspected cam-out detection means stops detecting the suspected cam-out while the tightening torque and torque rate are being monitored by the cam-out determination means. The cam-out detection system according to claim 1.

3. The predetermined angle is greater than a first angle at which the output shaft rotates from the time the tightening torque decreases due to an event other than the cam-out until the tightening torque exceeds a predetermined value, and simultaneously satisfies the condition that the torque rate is positive, and less than or equal to a second angle at which the output shaft rotates from the time the cam-out occurs until it is resolved. The cam-out detection system according to claim 1 or claim 2.

4. A cam-out detection system according to claim 1 or claim 2, A wear determination means determines that the wear of the bit has reached a certain level when the number of times or frequency at which the cam-out has occurred, as determined by the cam-out determination means, reaches a predetermined number or frequency. Having, Bit wear detection system.

5. A cam-out detection system for detecting cam-out of a bit mounted on the output shaft of a screw tightening device, Torque acquisition means that acquires the tightening torque during the tightening period in which the output shaft tightens the screw to be tightened via the bit, A cam-out determination means that determines that cam-out has occurred if the tightening torque does not exceed a second threshold during the monitoring period from when the tightening torque falls below a first threshold until the output shaft rotates by a predetermined angle, A cam-out detection system characterized by having the following features.

6. A cam-out detection system for detecting cam-out of a bit mounted on the output shaft of a screw tightening device, Torque acquisition means that acquires the tightening torque during the tightening period in which the output shaft tightens the screw to be tightened via the bit, Torque rate acquisition means for acquiring the torque rate of the tightening torque during the tightening period, A cam-out determination means determines that a cam-out has occurred if the tightening torque does not exceed the torque threshold during the monitoring period from when the torque rate falls below a rate threshold of 0 or less until the output shaft rotates by a predetermined angle, A cam-out detection system characterized by having the following features.

7. A computer program used in a computer that detects cam-out of a bit attached to the output shaft of a screw tightening device, To the aforementioned computer, The output shaft executes a torque acquisition process to acquire the tightening torque during the tightening period in which it tightens the screw to be tightened via the bit. A torque rate acquisition process is executed to acquire the torque rate of the tightening torque during the aforementioned tightening period. A cam-out detection process is executed if, during the monitoring period from when the torque rate falls below a first rate threshold of 0 or less until the output shaft rotates by a predetermined angle, there is no timing when the torque rate exceeds a second rate threshold of 0 or more and the tightening torque is equal to or greater than the torque threshold. A computer program characterized by the following features.

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