JPS6047073B2 - automatic screw tightening machine - Google Patents

Description

[Detailed Description of the Invention] The present invention temporarily tightens a screw to a workpiece, starts the final tightening after the temporary tightening is completed, and issues a final tightening completion signal when the shaft torque of the driver bit reaches a predetermined final tightening torque. This invention relates to an automatic screw tightening machine that completes screw tightening.

When tightening a screw onto a workpiece using this type of screwdriver, there is a certain probability that the screw will bite diagonally, the screw will come loose, or the screw will pop.

However, such a screw tightening failure cannot be detected as a tightening failure as long as the tightening torque reaches a predetermined final tightening torque. The method for detecting such defects as tightening defects is to look at temporal changes in tightening torque,
A possible method is to compare the change with the change over time when tightening is performed normally.

In other words, in general, the tightening torque of a screw changes over time as shown by the solid line in Figure 1 during normal tightening, but it may cause tightening defects such as diagonal biting of the screw or thread lifting. If the problem occurs, it will start up with a sudden change in time as shown by the broken line A in the same figure, and if the screw is abnormal and causes the neck to jump, etc., it will start up with a gradual change in time as shown in the broken line. Therefore, by detecting the temporal change in the tightening torque of a screw, it is possible to determine whether the screw has been tightened properly or not. However, in order to prevent this, the detection method becomes extremely complicated and the adjustment becomes difficult.

As a result, there is a drawback that the cost of the control device and the like increases. As a method to eliminate the above drawbacks,
There is an apparatus described in Japanese Patent No. 58. In addition to a configuration that detects temporal changes in the tightening torque of screws, this device is equipped with two timers, so that the time when screw tightening is completed is determined after a predetermined period of time has elapsed from the start of screw tightening. It is configured to determine whether or not the time has elapsed within a predetermined time, and to determine whether the tightening of the screw is good or bad based on the determination based on this time in addition to determining the temporal change in the tightening torque. Although this device eliminates the above-mentioned drawbacks, since the timer starts counting the time at the beginning of screw tightening, if the driver bit does not engage properly when fitting into the screw, it may actually cause the screw to tighten. Since the timing to start tightening differs for each task, the time required to fit the driver bit into the screw was evaluated in addition to the time required to actually tighten the screw. The time width of the timer setting time must be made extra wide, and as a result, new drawbacks arise, such as a decrease in determination accuracy. Therefore, the present invention provides a new means that can determine whether tightening is necessary with a low cost and simple configuration, instead of the method of looking at changes over time.

That is, the present invention is configured such that the motor is stopped and screw tightening is completed when the shaft torque of the driver bit that rotates in response to the rotation of the motor reaches a predetermined final tightening torque. Two timers having different set times are arranged to determine whether or not the screw tightening completion time is within a predetermined time, thereby determining whether the screw tightening is good or bad. The gist is that a comparator is provided to compare the torque with a temporary tightening torque lower than the actual tightening torque, and the timer is configured to start counting time based on the output of this comparator.

Next, one embodiment of the present invention will be described based on the drawings.

Fig. 2 shows a stationary single-axis automatic screw tightening machine as an example of an automatic screw tightening machine. ni rod 4
is inserted so that it can slide up and down. It is. A mounting member 6 for mounting a screw tightening machine main body 5 is inserted into the rod 4 so as to be slidable up and down, and a tension spring 46 connects the two. Further, this rod 4 is provided with a retaining ring (not shown), and the upper end of the rod 4 and the attachment member 6 are held at a constant distance. Further, a support plate for supporting a catcher 7 is slidably inserted into the rod 4, and is received by a nut 9 screwed into the lower end of the rod. The screw tightening machine main body 5 includes, for example, a pulse motor 10 and a driver bit 11 as a rotational drive source, and a driver bit 1 from the rotational drive source.
1 and a transmission shaft 12 that transmits rotational power, and the transmission shaft 12 is provided with a torque sensor 13 that detects the shaft torque of the driver bit. Further, this screw tightening machine main body 5 is configured to be able to move up and down by a lifting cylinder 14 provided on the support plate 2.
The lifting and lowering motion of the lifting cylinder 14 is also transmitted to the catcher 7 via the rod 4, so the catcher 7 also moves up and down together with the screw tightening machine body 5, but the amount of descent is determined by the upper end of the rod 4 and the upper arm. It is regulated by 3. Further, the catcher 7 can be locked to a nut 16a provided at the tip of a rod 16 of a cylinder serving as a driving means 15, and can be moved upwardly independently of the driver bit 11 by the operation of the driving means 15. It is. Although not shown, a switch for confirming return to the original position, such as a limit switch, which is turned on when the screw tightening machine main body 5 has been raised and returned to the original position is provided. The cylinder 14 and the driving means 15 are controlled by a circuit shown in FIG. 3, so as to perform an automatic screw tightening operation.

In FIG. 3, 21 is a screw tightening start part, 22 is a buffer amplifier that amplifies the detection signal of the torque sensor 13, 23 is a calibration that performs zero correction and gain correction of the detection signal, and 24 is a predetermined temporary tightening torque. A setter 25 is set with a predetermined final tightening torque value, and a lower limit torque setter 26 is set to the minimum required torque value when the final tightening is completed. Each of these setting devices 2
4 to 26 are, for example, 10-turn potentiometers. 27 is a comparator that compares the torque value detected by the torque sensor 13 and the temporary tightening torque value set in the setting device 24, and its output is counted by timers Te and Tf, which will be described later, via a timer m, which will be described later. Each is connected to the start terminal.

28 is a comparator for comparing the detected torque value and the main tightening torque value set in the setting device 25; 29 is a comparator for comparing the detected torque value and the lower limit torque value set in the setting device 26.

30 is a tightening defect reset section, 31 is a limit switch for confirming return of the screw tightening machine main body to its original position, and 32 is a cycle time over reset section.

Here, the cycle time refers to the time required for one screw tightening when screw tightening is normally performed. Therefore, if it takes more than this cycle time to tighten a screw, it means that there is something wrong with the screw tightening machine. Ta-Ti is a timer, and timer Ta is set to the cycle time. Timer n is set to the charging completion time.
Here, the charging completion time refers to the time from when a smoothing capacitor of a power supply unit (described later) that supplies power to the pulse motor 10 starts charging in response to a screw tightening start signal until charging is completed. This timer n is necessary because a pulse motor is used as the rotational drive source for the driver bit, and is unnecessary when using another motor. Timer Tc is set to machine time. Machine time is the time required to complete the final tightening when screws are tightened normally. While the cycle time was used as a guide to determine whether the screw tightening machine is normal or abnormal, the machine time is used to determine whether the screw is being tightened without any screws present or whether the screw is loose or not. This is the time that can be used as a guideline to determine whether the screw or workpiece is normal or abnormal. The timer Td is set to a break-in time after completion of temporary tightening.
The break-in time refers to the shaft torque detected by the torque sensor 13, including the initial detection error due to the material or abnormality of the workpiece or screw until completion, the transmission efficiency, and the transmission delay until it is transmitted to the screw. This refers to the time taken into consideration. It is necessary to adjust the length of this break-in time depending on the material of the workpiece or screw, and as a result, the tightening torque of the screw after break-in becomes equal to the shaft torque detected at that time. For example, when using urethane rubber as the workpiece, the transmission efficiency is poor and it takes time for the screw to adjust to the workpiece. The tightening torque of the screw changes gradually due to the effects of the body's unique characteristics, and it takes time until it becomes stable.
Therefore, in such cases, it is necessary to lengthen the break-in time. However, when a pulse motor is used as the rotational drive source, the minimum time of the timer Td for setting the running-in time should be determined by one pulse, because due to the characteristics of the pulse motor, it may rotate by one pulse. It is designed to take more than the corresponding amount of time. Te and Tf are two timers that are essential components of the present invention, and each counts the time at the same time as the main tightening starts. However, the setting time of one timer Te is the minimum required time for final tightening when no tightening defects have occurred, and the setting time of the other timer Tf is the minimum time required for final tightening when no tightening defects have occurred. Each is adjusted to the maximum required time for final tightening. The minimum and maximum required time for final tightening when no such tightening defects occur can be determined empirically. Normally, a large number of screws are tightened under the same conditions to find the standard final tightening time Ts (average value) and standard deviation σ, and TS-3σ is the minimum required time and TS+3σ is the maximum required time. Good. Statistically speaking, if the final tightening is done correctly, most of the tightening will be Ts±.
This is because it is included in the 3σ range. Of course, the minimum time and maximum time may be set to Ts±4σ, 5σ, etc. The timer Tg is set to a break-in time after the final tightening is completed. This break-in time has the same meaning as the break-in time after completion of temporary tightening described above. However, due to the characteristics of the pulse motor, even after the main tightening is completed, it may rotate for an extra pulse, so the minimum setting time of the timer Tg should be taken into consideration so that it is the time equivalent to this one pulse. There is. The timer Th starts counting time with a conversion completion signal from an AD converter (described later) which starts conversion when the timer Tg times out, and the time up is considerably delayed from the time when the main tightening is completed. This timer Th determines whether the final tightening torque is higher or lower than the set torque value of the lower limit torque setter 26. The timer Ti is set to the time required for the charge accumulated in the smoothing capacitor of the power supply section to be discharged after the power supply to the pulse motor drive circuit is cut off.

As long as electric charge is accumulated in the smoothing capacitor, the pulse motor is in an excited state and is restrained by the stop motion torque, so if the screw tightening machine main body 5 is moved upward in this state,
If the driver bit separates from the screw while torque is applied to the screw, damage to the workpiece may occur. Therefore, by providing the timer Ti, the screw tightening machine main body 5 can be raised after the pulse motor is de-energized and the rotating shaft becomes free.
Reference numeral 33 denotes a cycle time over detection section, which displays a cycle time over and issues a signal to the outside when the timer Ta times up. Reference numeral 34 denotes a machine time over detection section, which issues a machine time over signal when the timer Tc times out.

As will be described later, if this machine time-over signal is issued before the final tightening is completed, the screw tightening operation is terminated and a poor tightening signal is issued, regardless of the stage of the screw tightening operation. At the same time, the supply of the pulse train to the pulse motor 10 is stopped, and an operation command for the drive means 15 is issued. Completion of the screw tightening work means stopping the power supply to the pulse motor and returning the screw tightening machine to its original position. Since a machine time over is caused by an abnormality on the screw or workpiece side, such as the absence of a screw or a loose screw, the two timers Te. T
It is determined that the tightening is defective based on f, but it is meaningless to keep the pulse motor running until this determination is made, and it will be a waste of electricity, so the meaningless situation should be ended as soon as possible. In this sense, it was decided to issue a machine time-over signal and terminate the screw tightening work.
35 is a final tightening time determination unit that determines whether the time required for final tightening is between the time set in the timer Te and the time set in the timer Tf; 36 is a final tightening time determination unit that determines whether the time required for final tightening is between the time set in the timer Te and the time set in the timer Tf; A lower limit determining section 37 determines whether the detected torque is larger or smaller than the torque value set in the lower limit torque setting device 26, and the lower limit determining section 37 determines whether the detected torque is larger or smaller than the torque value set in the lower limit torque setting device 26. This is a judgment display section that displays whether the tightening is good or bad based on the results.

This display section 437 does not perform a display operation unless the timer Ti times up. 38 is a power supply unit for supplying power to the pulse motor 10, and when the screw tightening start unit 21 operates, it starts supplying power and starts the timer T.
When h times out, or the machine 3 time-over detection section 34 issues a detection signal, or the final tightening time judgment section 35 issues a judgment signal, power supply is stopped.

Reference numeral 39 denotes a double integral type AD converter that is resistant to noise, which converts the detected torque value when the timer Tg times up into a digital quantity and inputs it to the display drive unit 40.

Here, the detected torque value is set to A without going through the peak hold circuit.
-The reason why the input is directly input to the D converter 39 is because, in the case of a pulse motor, the rotating shaft under excitation and stop of supply pulses is in a stopped rotation state and is restrained by stall torque. Because there is. Therefore, when a motor other than a pulse motor is operated, the rotating shaft becomes free when rotation is stopped, so it is necessary to temporarily hold the detected torque value in a peak hold circuit and then input it to the AD converter. Since the display driving section 40 is synchronized to have the same display timing as the judgment display section 37, the A-D converter 39
(display on the display section 37 for determining the digital quantity input from)
It is outputted at the same timing as , and digitally displayed on the display 41. 42 is a preliminary tightening comparator 27 and a final tightening comparator 28
A solenoid valve 43, which operates the lifting cylinder 14 and the driving means 15 according to the output signal of a microcomputer, for example, is used as a logic circuit for calculating and processing signals such as the comparison output of , the output of timers TO, Td, and Ti, etc. 44 is controlled to be energized or de-energized, and the pulses supplied to the pulse motor drive circuit 45 are switched between high speed and low speed and are supplied.

This switching is performed at the stage when temporary tightening is completed. A high-speed pulse is a pulse that is higher than the self-starting frequency of the pulse motor 10, and a low-speed pulse is a pulse that is lower than the self-starting frequency. When a high-speed pulse is applied, the pulse motor 10 rotates at high speed,
When a slow pulse is applied, it rotates at a slow speed. The reason why the pulse motor 10 is rotated at high speed until the temporary tightening stage is to shorten the screw tightening time.
The reason why it is set to rotate at a low speed at the stage of starting the final tightening is to enable highly accurate torque control. Next, the automatic screw tightening operation with the above configuration will be explained according to the flowchart shown in FIG.

The power supply unit 38 that operates the screw tightening start unit 21 operates and starts supplying power to the pulse motor drive circuit 45, and at the same time, the torque indicator 41 and the judgment display unit 37 are reset, and the timers Ta and Tb start counting time. Start. When the smoothing capacitor of the power supply unit 38 is fully charged and the timer Tb times out, the logic circuit 42 issues a command to supply a high-speed pulse train and lower the pulse, and the pulse motor 10 starts rotating at high speed, and the screw tightening machine main body 5 descends and starts temporary tightening work. Also, at the same time, the timer Tc starts counting time. If there is no abnormality in the temporary tightening work, the timer Tc will not time out during the work, but if there is an abnormality, such as a screw being twisted in the catcher, and the temporary tightening is not completed, Timer Tc times out during temporary tightening. Then,
A machine time over signal is applied to the logic circuit 42, the power supply section 38, and the timer Til judgment display section 37, and the supply of the pulse train is stopped, and at the same time, the operation command of the drive means 15, the end of the screw tightening work, and the indication of poor tightening are given. will be carried out. However, the indication of poor tightening is not made until the timer Ti times out. The reason for issuing the operation command for the drive means 15 using this machine time-over signal is that this command raises the rickshaw 7 and ejects the screws in the catcher 7, thereby allowing the next screw tightening operation to be performed. This is to avoid a situation where two screws are present in the catcher 7. In the flowchart, 1 indicates a tightening failure indication, 2 indicates the start of returning the screw tightening machine main body 5 to its original position, and 3 indicates a display command due to time-up of the timer Ti. Note that when the second home position return operation is started, the fifth
As shown in the figure, power supply to the pulse motor 10 is also stopped at the same time. On the other hand, there was no abnormality in the temporary tightening work.
When the detected torque value of the torque sensor reaches the pre-tightening torque value of the setter 24 by the time the timer Tc times up and a pre-tightening completion signal is issued from the comparator 27, the timer Td starts counting time and the logic circuit 42 The supply of the high-speed pulse train is stopped from then, and at the same time, a driving means activation command is issued. The pulse motor 10 stops rotating by stopping the supply of the pulse train, and the driving means 15 is activated by the driving means activation command. Since the catcher 7 is raised independently by the operation of the drive means 15, even if the head of the temporarily tightened screw is held or caught in the catcher when the temporary tightening is completed, the catcher 7 will not move up. After rising, this condition is resolved, and the torque sensor 13 can now detect only the shaft torque that is purely involved in the tightening torque. After the temporary tightening is completed, the screw becomes familiar with the workpiece and the timer Td times out, a low-speed pulse train supply pulse is emitted from the logic circuit 42, and the final tightening is performed while rotating the pulse motor 10 at a low speed below the self-starting frequency. .
Also, at the same time as the main tightening starts, two timers are activated. Tf
starts counting time. In this case, if the timer Tc times out even though the final tightening has not yet been completed due to an abnormality such as loose screws, the supply of the pulse train to the pulse motor 10 is stopped, as in the case of the temporary tightening failure described above. At the same time, the screw tightening work is completed and a tightening failure indication 1 is displayed. On the other hand, if there is no abnormality in the screw and the detected torque value of the torque sensor 13 reaches the final tightening torque value of the setting device 25, the comparator 28
A final tightening completion signal is issued.

Then, based on this signal, the supply of the low-speed pulse train from the logic circuit 42 is stopped, and the pulse motor 10 stops rotating. At the same time, timers Tc and Tf are reset, and timer Tg starts counting time. In this case, the quality of the tightening is determined depending on whether the final tightening completion signal is issued before or after the timers Te and Tf time up. If the final tightening completion signal is issued before the timer Te has timed out or after the timer Tf has timed out, the screw may be jammed diagonally, the neck may be skipped, or some other abnormality may occur. Since this has occurred, the screw tightening work is completed and a tightening failure indication 1 is displayed. On the other hand, the time when the final tightening completion signal is issued is after the timer Te times out.
If it is before the timer Tf times out, the final tightening has been completed normally, so wait until the timer Tg times out, operate the A-D converter 39, and start the timer T.
The torque value detected by the torque sensor 13 at the time when g times out is digitally converted and input to the display drive section 40. The display driving section 40 temporarily holds this input signal and operates to display it at the same timing as the judgment display section 37.
When the A/D converter 39 operates and outputs a conversion completion output, the timer Th starts counting time.

The lower limit determining section 36 performs a determining operation based on the time-up signal of the timer Th. Through this judgment operation,
After the final tightening is completed, the timers Tg and Th. It is determined whether the torque value detected by the torque sensor 13 at the time after the time and the A-D conversion time is higher or lower than the lower limit torque value of the setter 26. In this way, we selected the detected torque value after a considerable amount of time has passed after the completion of the final tightening as the subject of judgment, considering that this is equivalent to an extension of the break-in time after the completion of the final tightening. It is a last resort and a message. Therefore, this time has the same meaning as the break-in time after completion of temporary tightening and final tightening, and if the time is made a little longer, stress relaxation, tightening torque becomes larger, or temperature increases. It is also taken into consideration that the tightening torque tends to decrease due to the creep phenomenon, etc., which is accelerated by this process. If the detected torque value is lower than the lower limit torque value of the setting device 26, the torque is insufficient, so wait for the timer Ti to time up and use the display command 3 to display the judgment display section 37.
indicates poor tightening. On the other hand, if the detected torque value is higher than the lower limit torque value of the setter 26, the timer T
After waiting for the time of i to elapse, the judgment display section 37 displays the indication that the tightening is good according to the display command 3, and the display drive section 40
The display 41 digitally displays the detected torque values held in the respective positions. Further, when the lower limit determining section 36 makes the above determination, the screw tightening work is completed regardless of whether the result of the determination is good or bad. Next, the operation of returning the screw tightening machine main body 5 to its original position will be explained based on the flowchart shown in FIG.

As mentioned above, the condition for starting 2 for returning the screw tightening machine body 5 to its original position is when the timer Th times up, or when the timer Tc times up and exceeds the machine time, or when the main tightening time determination unit 35 This is when an abnormal signal is issued. According to this start condition, the power supply from the power supply section 38 to the pulse motor drive circuit 45 is stopped,
At the same time, timer Tj starts counting time. Eventually timer T
When i becomes time-fast and the rotating shaft of the pulse motor 10 becomes free, a rising command is issued from the logic circuit 42 and the lifting cylinder 14 starts moving upward. Further, a command 3 for displaying a tightening pass/fail judgment on the judgment display section 37 when the timer Ti times up. is issued, and at this point the judgment display section 37 displays the aforementioned indication of poor tightening or good tightening. At this time, the detected torque value held in the display drive section 40 is simultaneously displayed on the display 41. The screws are tightened by the upward movement of the lifting cylinder 14. - When the machine body 5 eventually returns to its original position, the timer Ta is reset, and the logic circuit 42 issues a deactivation command to lower the drive means 15.

The catcher 7 is lowered by the lowering of the drive means 15, returning to a state in which it can accept a new screw. in this case,
Even if the logic circuit 42 issues a raise command, the screw tightening machine main body 5 does not return to its original position, and therefore, when the timer Ta times out, the cycle time over detection section 33 displays a cycle time over display. In addition, when the cycle time is over, the screw tightening start section 21 operates and the screw tightening machine main body 5
This is performed no matter when the timer Ta times out after the has descended from the original position. This cycle time over display indicates that there is an abnormality on the screw tightening machine side.
Appropriate repair work can be carried out. Although the present embodiment has been described with respect to a stationary single-shaft type automatic screw tightening machine, similar effects can be obtained with a stationary multi-shaft type automatic screw tightening machine.

In addition to the determination based on temporal changes in tightening torque, the present invention
Since the structure is configured to judge the quality of screw tightening by determining whether the screw tightening is completed within a predetermined time after the actual tightening starts after reaching the preliminary tightening torque, Not only is it possible to reliably detect tightening defects such as diagonal chamfering and thread lifting, but even when the timing of chamfering when the driver bit fits into the screw may differ for each job, it is possible to accurately detect the timing of the chamfering when screw tightening is completed. The timer that makes the determination is configured to start counting the time after starting the final tightening, so the time is counting from the time when the driver bit and the screw are securely engaged, so the initial mating timing This has the advantage that it is possible to make a time-based judgment based on the time required for actual screw tightening, regardless of the difference in the number of screws, and that extremely accurate judgment can be made.

[Brief explanation of the drawing]

Figure 1 is a diagram showing temporal changes in screw tightening torque, Figure 2
The figure is a side view of an automatic screw driver showing an embodiment of the present invention, FIG. 3 is an electric circuit diagram of the screw driver, and FIG. Flowchart FIG. 5 is a flowchart illustrating the operation of returning the screw tightening machine to its original position. 11...Driver bit, Te, Tf...
...Two timers.

Claims (1)

[Claims] 1. The driver bit is rotationally driven by a motor, the shaft torque of the driver bit is detected by a torque converter, and a comparator is provided to compare a set value corresponding to a desired tightening torque value with the detection output of the torque converter, When the detection voltage of the torque converter matches the set value, the motor is stopped and screw tightening is completed, while two timers with different set times are provided with a predetermined time width to complete screw tightening. In an automatic screw tightening machine configured to determine whether screw tightening is good or bad based on the output state of the timer at the time of completion,
A comparator is installed to compare the detection output of the torque converter with a set value corresponding to a temporary tightening torque lower than the desired tightening torque, and the output of this comparator is connected to the time counting start terminal of each of the two timers. An automatic screw tightening machine characterized in that the timer starts counting time at the same time as the main tightening starts.