JPS635228B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a pulse motor, a driver bit that is rotationally driven by the motor to tighten a screw to a workpiece, and a torque sensor that detects the shaft torque of the driver bit. The present invention relates to an automatic screw tightening machine configured to cut off the supply of drive pulses to a pulse motor when the detected shaft torque reaches a predetermined final tightening torque.

This type of automatic screw tightening machine detects the axial torque of the driver bit with a torque sensor, and compares this detected torque value with a predetermined main tightening torque while supplying drive pulses to the pulse motor or stopping the torque. control is in place. Therefore, even if the shaft torque detected by the torque sensor is not separately displayed at the time when the final tightening is completed, the tightening torque of the screw should theoretically match the predetermined final tightening torque. However, in reality, there is some time delay before the axial torque of the driver bit is transmitted to the screw due to the material of the screw or workpiece or its abnormality, and especially when an elastic body such as urethane rubber is used as the workpiece. Due to the inherent characteristics of the elastic body, the tightening torque of the screw gradually changes after the pulse motor stops when the final tightening is completed, so the actual tightening torque of the screw in a stable state may differ from the predetermined final tightening torque value. There is a tendency for the value to be low. Furthermore, since the driver bit is rotated by a pulse motor, due to the characteristics of the pulse motor, even after the final tightening is completed, the pulse motor may rotate for one extra pulse until it stops. The tightening torque of the screw increases by an amount corresponding to the rotation angle. For the above reasons, in practice, the tightening torque of a screw often does not match the specified final tightening torque value, not only at the time of completion of final tightening, but also after that. The disadvantage is that it is not possible to adequately control the quality of the product.

In this respect, the present invention maximizes the characteristic of a pulse motor that even if the supply of drive pulses to the pulse motor is stopped and the rotation is stopped, the drive shaft is held at stall torque as long as it is energized. This new automatic screw screw is designed to separately display the torque value detected by the torque sensor after a certain period of time after cutting off the supply of drive pulses when the final tightening is completed. The company provides a tightening machine.

That is, the present invention is configured such that the supply of drive pulses to the pulse motor is stopped when the shaft torque of the driver bit, which rotates in response to the rotation of the pulse motor, reaches a predetermined final tightening torque. The gist of this invention is to provide a timer that starts counting the time from , and a display that displays the shaft torque value based on the time-up signal of this timer. When implementing the present invention, in order to shorten the time from the start of screw tightening to the completion of final tightening, a torque value slightly lower than the actual tightening torque value is set as the temporary tightening torque, and the shaft torque is set as the temporary tightening torque. It is desirable to rotate the pulse motor at high speed until the torque is reached. However, in the final tightening operation after the shaft torque reaches a predetermined pre-tightening torque and the pre-tightening is completed, it is preferable to rotate the pulse motor at a low speed. This is because it is desirable to perform torque control as accurately as possible during final tightening. Also, the display of the shaft torque value at the time the timer expires is as follows:
Although it may be done at the same time as the timer times up, it is preferable to do it after the screw tightening operation is finally completed. Furthermore, although the shaft torque may be displayed in an analog quantity, it may also be displayed in a digital quantity. Incidentally, the break-in time taken into consideration in the setting time of the timer will be explained in the embodiment.

Next, one embodiment of the present invention will be described based on the drawings. Figure 1 shows a stationary single-shaft type automatic screw tightening machine as an example of an automatic screw tightening machine.
Reference numeral 2 denotes a support plate attached to the support column, and a rod 4 is inserted into arm portions 3, 3 at the upper and lower ends of the support plate so as to be vertically slidable. 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. Furthermore, a support plate 8 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 a pulse motor 10, a driver bit 11, and a transmission shaft 12 that transmits rotational power from the driver bit 11 to the driver bit 11.
The transmission shaft 12 is equipped with a torque sensor 13 that detects the shaft torque of the driver bit.
is provided. In addition, this screw tightening machine main body 5
is the lifting cylinder 14 provided on the support plate 2.
It is configured to be able to move up and down. The vertical movement 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 3. regulated by. The catcher 7 is connected to a nut 16 provided at the tip of a rod 16 of a cylinder serving as a driving means 15.
a, and can be moved upwardly independently of the driver bit 11 by the operation of the drive means 15. Although not shown, a switch for confirming return to the original position is provided, such as a limit switch, which is turned on when the screw tightening machine main body 5 is raised and returned to the original position. The pulse motor 10, the lifting cylinder 14, and the driving means 15 are the second
It is controlled by the circuit shown in the figure to perform an automatic screw tightening operation. In FIG. 2, 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. 25 is a setting device where a predetermined final tightening torque value is set, 26 is a lower limit set to the final minimum required torque value as a product judgment after final tightening is completed. It is a torque setting device. For each of these setting devices 24 to 26, for example, a 10-turn potentiometer is used. 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; 28 is a comparator that compares the detected torque value and the actual tightening torque value set in the setting device 25; A comparator 29 is a comparator that compares the detected torque value and the lower limit torque value set in the setting device 26. 30 is a reset part for poor tightening, 31 is a limit switch for confirming the return of the screw tightening machine body to its original position, 3
2 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 to Ti are timers, and timer Ta is set to the cycle time. Timer Tb is set to the charge completion time. Here, the charge 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. Timer Tc is set to machine time. Machine time refers to the time from the start of tightening to the completion of final tightening when screw tightening is performed 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 tightening operation is being performed without any screws present or whether the screws are loose or not. This is the time that can be used as a guide to determine whether the screw or workpiece is normal or abnormal. timer
Td is set to the 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 account. This break-in time needs to be adjusted 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, and the shaft torque at the time of completion of tightening. tend to be different. 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. Due to the effects of the body's unique characteristics, the tightening torque of the screw changes gradually and takes time to stabilize. Therefore, in such cases, it is necessary to lengthen the break-in time.
However, the minimum time of timer Td for setting the break-in time is
Due to the characteristics of the pulse motor that rotates the driver bit, it may rotate for one pulse more than the other, so consideration is given to the time being longer than the time equivalent to this one pulse.

Timers Te and Tf each count the time at the same time as the main tightening starts. However, the setting time of one timer Te is
The setting time of the other timer Tf is adjusted to the minimum time required for final tightening when no tightening defects have occurred, and the setting time of the other timer Tf is adjusted to the maximum required time for final tightening when no tightening defects have occurred. It has been done. The minimum and maximum required time for final tightening when no such tightening defects occur can be determined empirically. Normally, the standard final tightening time Ts (average value) is obtained by tightening many screws under the same conditions.
and the standard deviation δ, and set Ts−3δ as the minimum required time and Ts+3δ as the maximum required time. This is because if the final tightening is done statistically normally, most of the tightening will be within the range of Ts±3δ.
Minimum time, maximum time Ts±4δ, 5δ
Of course, it is also possible to set the value to . Timer Tg
is a timer which is an essential component of the present invention, and is set to the 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 if the final tightening is completed, there may be an additional rotation of one pulse, so the minimum setting time of the timer Tg is as follows:
The time corresponding to this one pulse is also taken into consideration. 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 up, and the time up is considerably delayed from the time when the main tightening is completed. When the timer Th times up, it is instantly determined 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 pulse motor drive circuit to be discharged after the power supply to the pulse motor drive circuit is cut off. As long as charge is stored in the smoothing capacitor, the pulse motor is in an excited state and is restrained by stall torque.
When the screw tightening machine body 5 is moved upward in this state,
The driver bit will separate from the screw while torque is applied to the screw, resulting in damage to the workpiece. Therefore, by providing this timer Ti, the screw tightening machine body 5 can be raised after the excitation of the pulse motor is released and the rotating shaft is in a free state.

33 is a cycle time over detection section, which is a timer
When Ta times up, a cycle over is displayed and a signal is sent to the outside. Reference numeral 34 denotes a machine time over detection section, which issues a machine time over signal when the timer Tc times up. 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 a drive 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. Machine time overs occur because there are no screws,
Since this is an abnormality on the screw or workpiece side called screw looseness, even if the machine time over signal is not issued after temporary tightening is completed, the two timers Te
Tf determines that the tightening is defective, but it is pointless to keep the pulse motor running until such a determination is made, and it would be a waste of electricity.
It was decided to issue a machine time-over signal and end the screw tightening work in order to end the process as quickly as possible without making any sense. 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 timer
a lower limit determination unit 37 that determines whether the detected torque when Th times up is larger or smaller than the torque value set in the lower limit torque setter 26;
is a determination display section that displays the quality of tightening based on the signals from each of the determination sections 35 and 36 and the machine time-over detection section 34. This judgment display section 37
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 a start unit 2
When 1 is activated, power supply starts and timer Th
When the time has expired or the machine time over detection section 34 or the final tightening time determination section 35 issues a detection signal, power supply is stopped. 39 is a double integral type A-D converter that is resistant to noise, and the torque sensor 13 at the time when timer Tg times up.
The detected torque value is converted into a digital quantity and input to the display driving section 40. Here, the detected torque value is input directly to the A-D converter 39 without going through the peak hold circuit. In the case of a pulse motor, the rotating shaft that is under excitation and when the drive pulse supply is stopped is in the stopped rotation state. This is because, at the same time, it is restrained by stall torque. Since the display driving section 40 is synchronized to display at the same timing as the judgment display section 37, the display drive section 40 displays the digital quantity input from the A-D converter 39 at the same timing as the display on the judgment display section 37. Although not shown, the output is output only when the tightening is determined to be normal, and is digitally displayed on the display unit 41. However, the displayed value is the torque value detected by the torque sensor 13 at the time when the above-mentioned timer Tg times out. 42 is a microcomputer, for example, as a logic circuit for processing signals such as the comparison outputs of the temporary tightening comparator 27 and the final tightening comparator 28, and the outputs of timers Tb, Td, and Ti.
The output signal controls the energization and de-energization of the solenoid valves 43 and 44 that operate the lifting cylinder 14 and the driving means 15, and also transmits, switches, and stops high-speed and low-speed pulse trains supplied to the pulse motor drive circuit 45. is controlled. This switching is performed when temporary tightening is completed, and the stop is performed when temporary tightening and final tightening are completed, or when the timer Tc times up and exceeds the machine time.The transmission of high-speed and low-speed pulse trains is performed by a microcomputer. It is done. 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 automatic frequency.

Next, the automatic screw tightening operation with the above configuration will be explained according to the flowchart shown in FIG. When the screw tightening start section 21 operates, the power supply section 3
8 operates and starts supplying power to the pulse motor drive circuit 45, the torque indicator 41 and judgment display section 37 are reset, and the timers Ta,
Tb starts counting time. When the smoothing capacitor of the power supply unit 38 has completed charging and the timer Tb has timed up, the logic circuit 42 issues a command to supply and lower the drive pulses of the high-speed pulse train, 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, timer Tc starts counting time. If there is no abnormality in the temporary tightening work, the timer Tc will not time up 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, the temporary tightening will not be completed. During this time, timer Tc times up. Then, a machine time-over signal is applied to the logic circuit 42, power supply section, timer Ti, and judgment display section 37,
The supply of the high-speed pulse train is stopped, and at the same time, a command to operate the drive means 15, completion of the screw tightening operation, and an indication of poor tightening are given. However, the indication of poor tightening is not made until the timer Ti times up. The reason for issuing an operation command for the drive means 15 using this machine time-over signal is that this command raises the catcher 7 and ejects the screws inside the catcher 7, so that the next screw tightening operation can be performed. This is to avoid a situation where two screws are present in the catcher 7. In the flowchart, indicates the tightening defect display, indicates the start of returning the screw tightening machine body 5 to its original position, indicates the judgment display command due to the time-up of the timer Ti, and indicates the timer
This shows the torque display command when the tightening was normal at the time of Ti time-up. Incidentally, when the operation of returning to the original position is started, the power supply to the pulse motor 10 is also stopped at the same time as shown in FIG. On the other hand, if there is no abnormality in the temporary tightening work, and the detected torque value of the torque sensor reaches the preliminary tightening torque value of the setting device 24 before the timer Tc times out, and the comparator 27 issues a temporary tightening completion signal, the timer Td is activated. At the same time as time counting begins, the supply of the high-speed pulse train from the logic circuit 42 is stopped, 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 screw is held or caught in the catcher 7 when the temporary tightening is completed, the catcher 7 will not be raised. After that, this condition will be resolved, and the torque sensor 13 will be able to detect only the shaft torque that is purely involved in the tightening torque.

After the temporary tightening is completed, the screw will fit into the workpiece and the timer will start.
When Td times up, a low-speed pulse train drive pulse is issued from the logic circuit 42, and final tightening is performed while rotating the pulse motor 10 at a low speed below the self-starting frequency. Then, at the same time as the main tightening starts, two timers Te and Tf start 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 low-speed pulse train to the pulse motor 10 will be activated, as in the case of poor tightening at the temporary tightening stage described above. The supply is stopped, and at the same time, the screw tightening work is completed and a tightening failure is displayed.

On the other hand, when there is no abnormality in the screw and the torque value detected by the torque sensor 13 reaches the final tightening torque value of the setting device 25, the comparator 28 issues a final tightening completion signal. 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, timer Tc,
Tf is 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 time when the final tightening completion signal is issued before timer Te times up or after timer Tf times up, the screw may bite diagonally or cause some kind of abnormality such as neck skipping. Therefore, the screw tightening work is completed and a tightening failure is displayed. On the other hand, the time when the final tightening completion signal is issued is after the timer Te has timed up and
If it is before the time-up of Tf, since the final tightening has been completed normally, the A-D converter 39 is activated as soon as the timer Tg times-up.
The torque value detected by the torque sensor 13 at the time when the timer Tg times out is digitally converted and inputted to the display drive unit 40. The display drive section 40 temporarily holds this input signal and operates to display it at the same timing as the judgment display section 37 and when the tightening is normal.

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 determination operation, it is determined whether the torque value detected by the torque sensor 13 at the time after the timer Tg and Th time and the A-D conversion time after the completion of main tightening is higher or lower than the lower limit torque value of the setting device 26. . The reason why we selected the detected torque value after a considerable amount of time had passed after the completion of the final tightening as the subject of judgment was because we considered this to be equivalent to an extension of the break-in time after the completion of the final tightening, and used this as the final means of determining whether the tightening was successful. This is for the purpose of writing. 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, the stress relaxation and tightening torque will become larger, or the temperature will increase. 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 setter 26, the torque is ultimately insufficient, so the timer Ti
After waiting for the time to elapse, the determination display section 37 displays an indication of poor tightening in accordance with the determination display command. On the other hand, if the detected torque value is higher than the lower limit torque value of the setting device 26, wait for the timer Ti to time up, and in response to the judgment display command, the judgment display section 37 will display the indication that the tightening is good, and also display the torque. The display 41 digitally displays the detected torque value held in the display drive unit 40 according to the command. Furthermore, 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 screw tightening machine main body 5 returns to its original position in the fourth step.
The explanation will be based on the flowchart shown in the figure. As mentioned above, the conditions for starting the return of the screw tightening machine main body 5 to its original position are when the timer Th times up, or when the timer Tc times up and exceeds the machine time, or when an abnormality occurs from the main tightening time determination section 35. That's when I did it. With this starting condition,
From the power supply section 38 to the pulse motor drive circuit 45
The power supply to is stopped, and at the same time, timer Ti starts counting time. When the timer Ti eventually expires 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 begins to move upward. In addition, the judgment display section 3
At step 7, a command is issued to display a judgment on whether the tightening is successful or not, and at this point, the judgment display section 37 displays the above-mentioned insufficient tightening or good tightening. At this time, if a torque display command is issued, the detected torque value held in the display drive unit 40 is displayed on the display 41 at the same time.

When the screw tightening body 5 eventually returns to its original position due to the upward movement of the lifting cylinder 14, the timer starts.
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 an ascending command, the screw tightening machine body 5 does not return to its original position, and therefore the timer
When Ta times up, the cycle time over detection section 33 displays a cycle time over display. Incidentally, the cycle time over display is performed even if the timer Ta times out at any point after the screw tightening machine main body 5 is lowered from the original position. This cycle time over display indicates that there is an abnormality on the screw tightening machine side, and appropriate repair work can be carried out.

As explained above, the automatic screw tightening machine according to the present invention is provided with a timer that stops supplying drive pulses to the pulse motor when the shaft torque of the driver bit reaches the main tightening torque, and starts counting time from this point. Since it is configured to display the shaft torque based on the time-up signal of this timer, it may take some time for the shaft torque to be transmitted to the screw depending on the material of the screw or workpiece, or even after the final tightening is completed. The tightening torque of the screw gradually fluctuates,
In stable conditions, the screw tightening torque may differ from the specified main tightening torque, and after the final tightening is complete, the pulse motor rotates one extra pulse for control purposes, which increases the screw tightening torque. However, the timer Tg will display the shaft torque as the screw tightening torque at the time when these factors are considered. Therefore, the most important data for quality control of finished products can be obtained, thereby contributing to improving the reliability of finished products and the product price. In addition, since a pulse motor is used to rotate the driver bit, even if the drive pulses are stopped upon completion of final tightening, the pulse motor will continue to operate as long as power is being supplied to the pulse motor drive circuit. The rotating shaft is restrained by stall torque in a stopped state. Therefore, the shaft torque, which is the actual tightening torque of the screw at the time when the timer Tg times up, can be directly led to and displayed on the display section, which has the advantage of being able to perform torque management that is more product-oriented. Furthermore, the peak hold circuit required to display the maximum value of shaft torque is not required, and the number of parts can be reduced accordingly.
Although the embodiments show examples in which the present invention is applied to a single-shaft type screw tightening machine, it goes without saying that the present invention can also be applied to a multi-shaft type screw tightening machine.

[Brief explanation of the drawing]

FIG. 1 is a side view of an automatic screw tightening machine showing an embodiment of the present invention, FIG. 2 is an electric circuit diagram of the screw tightening machine,
3A, 3B, and 3C are flowcharts for explaining the screw tightening operation of the screwdriver, and FIG. 4 is a flowchart for explaining the return operation of the screwdriver to its original position. 10...Pulse motor, 11...Driver bit, 13...Torque sensor, Tg...Timer.

Claims (1)

[Scope of Claims] 1. A pulse motor, a driver bit rotationally driven by the pulse motor, and a detection sensor that detects the shaft torque of the driver bit, and the shaft torque detected by the torque sensor reaches a predetermined value. In an automatic screw tightening machine configured to cut off the supply of drive pulses to the pulse motor when the tightening torque is reached, a timer is installed that starts counting the time when the shaft torque of the driver bit reaches the main tightening torque. An automatic screw tightening machine characterized by being equipped with a display that displays the shaft torque value based on a time-up signal.