JPS6357171B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a pulse motor, a driver bit that is rotationally driven by the pulse 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 issue a final tightening completion signal when the shaft torque reaches a predetermined final tightening torque value, and at the same time cut off the supply of drive pulses to the pulse motor.

In this type of automatic screw tightening machine, the shaft torque of the driver bit is detected by a torque sensor.
Torque control is performed by controlling the drive pulses to the pulse motor while comparing this detected torque value with a predetermined final tightening torque value set in a torque setting device or the like. Therefore, when the shaft torque of the driver bit reaches the final tightening torque value, the supply of drive pulses to the pulse motor is stopped, the driver bit is stopped, the driver bit is restrained to the stall torque, and the power supply section is At the same time, the power supply to the pulse motor drive circuit is cut off and the driver bit is raised to return to its original position. However, the power supply section uses a capacitor with a relatively large capacity because the pulse motor itself requires a relatively stable supply voltage and a relatively large current, and this capacitor affects the power supply to the pulse motor drive circuit. Even if the supply is cut off, it takes time for the charge charged in the capacitor to be discharged, and the pulse motor is still in an excited state due to the voltage caused by this discharge transient charge, so the driver bit is constrained to a certain torque. in a state. This certain torque is close to the stall torque if the discharge transient charge is close to the charge during charging, and close to the free state if it is close to the charge during discharge. Therefore, if the driver bit is raised and returned to its original position in this uncertain transient state of restraint, the driver bit will rise with the screw screwed into the work piece firmly engaged, and at this time the screw will However, there are disadvantages in that the screw is slightly screwed in, causing the shaft torque to rise above the set final tightening torque value, causing damage to the screw head or workpiece, or damage to the driver bit.

The present invention aims to eliminate the above-mentioned drawbacks, and embodiments thereof will be described below with reference to the drawings. Fig. 1 shows a stationary single-shaft automatic screw tightening machine as an example of an automatic screw tightening machine. A rod 4 is inserted into the holder so as to be slidable up and down. 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 is assembled from a pulse motor 10, a driver bit 11, and a transmission shaft 12 that transmits rotational power from the rotational drive source 10 to the driver bit 11. A torque sensor 13 is provided to detect the torque. 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.
Although the main body 5 of the screw tightening machine moves up and down, the amount of descent thereof is regulated by the upper end of the rod 4 and the upper arm 3. In addition, the catcher 7 is driven by a drive means 15.
The driving means 1 can be locked to a nut 16a provided at the tip of the rod 16 of the cylinder.
By the operation 5, the upward movement is possible independently of the driver bit 11. 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 pulse motor 10, the lifting cylinder 14, and the driving means 15 are controlled by a circuit shown in FIG. 2 to perform an automatic screw tightening operation. In Figure 2, 21
22 is the screw tightening start part, and 22 is the torque sensor 13.
a buffer amplifier for amplifying the detection signal; 23, a calibration for correcting and gain correction of the detection signal; 24, a setting device in which a predetermined temporary tightening torque value is set; and 25, a predetermined final tightening torque value. The setting device 26 is a lower limit torque setting device that is finally set to the minimum required torque value as a product judgment when the main tightening is completed. 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. 3
0 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,
Cycle time refers to the time required for one screw tightening when screw tightening is performed normally. 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 (Tc) are timers, and the timer (Ta) is set to the cycle time. The 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. The 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. The 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 screw tightening torque after break-in is equal to the shaft torque detected at that time, and is equal to the shaft torque when the final tightening is completed. 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 become familiar with the workpiece. The tightening torque of the screw changes gradually due to the influence of its unique characteristics, and it takes time for it to become stable.
Therefore, in such cases, it is necessary to lengthen the break-in time. However, due to the characteristics of the pulse motor that rotates the driver bit, the minimum time of the run-in time setting timer (Td) may exceed the time equivalent to one pulse, as it may rotate by one pulse. This is taken into consideration.

The timers (Te) and (Tf) each count the time at the same time as the final 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 time is adjusted to the maximum required time for final tightening in cases where there is no actual tightening. The minimum and maximum required time for final tightening when no such tightening defects occur can be determined empirically. usually,
Tighten a large number of screws under the same conditions to find the standard final tightening time T _S (average value) and standard deviation σ, and calculate T _S −3σ
may be set as the minimum required time, and T _S +3σ may be set as the maximum required time. This is because if the final tightening is performed statistically normally, most of the tightening will be within the range of T _S ±3σ. Of course, the minimum time and maximum time may be set to T _S ±4σ, 5σ, etc. The timer (Tg) is a timer set for 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 after the final tightening is completed, it may rotate for an extra pulse, so the minimum setting time of the timer (Tg) takes into account the time equivalent to this one pulse. .
The timer (Th) is an A-D converter (described later) that starts conversion when the timer (Tg) times up.
Time counting starts at the conversion completion signal, and the time-up is considerably delayed from when the main tightening is completed. When the timer (Th) times out, 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. 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 stall torque, so if the screw tightening machine body 5 is moved upward in this state, torque will be applied to the screw. In this state, the driver bit will separate from the screw, causing damage to the workpiece. Therefore, by providing this timer (Ti), the screw tightening machine main body 5 can be raised after the excitation of the pulse motor is released and the rotating shaft is in a free state. As is clear from the drawing, this timer (Ti) starts counting time in response to the time-up signal of the timer (Th), so at the time the timer (Th) times up, the pulse motor 10
The rotating shaft is restrained by a stall torque, and detection by a lower limit determining section 36, which will be described later, is completed instantaneously. Therefore, the tightening torque of the screw at the time when the timer (Th) times up can be detected by the torque sensor 13, and the lower limit determination section 36 can make a final determination of the tightening torque.

33 is a cycle time over detection section which, when the timer (Ta) times up, displays a cycle time over and issues a signal 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. If this machine time-over signal is issued before the final tightening is completed, the screw tightening operation is terminated and a tightening failure 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 are caused by abnormalities on the screw or workpiece side, such as missing screws or loose screws, so even if the machine time over signal is not issued after temporary tightening is completed, two timers (Te) will eventually be activated. (Tf), it is determined that the tightening is defective, but it is pointless to keep the pulse motor running until such a determination is made, and it is a waste of electricity, so it is necessary to eliminate this pointless condition as soon as possible. The decision was made to issue a machine time-over signal to signal the end of the screw tightening work. 35
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 that determines whether the detected torque at the time of time-up is larger or smaller than the torque value set in the lower limit torque setting device 26 includes the respective determining sections 35 and 36.
and a determination display unit that displays the quality of tightening based on the signal from the machine time-over detection unit 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. When the start unit 21 is activated, power supply is started, and the timer (Th) times up.
Alternatively, when 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 that is resistant to noise.
-D converter converts the detected torque value of the torque sensor 13 at the time when the timer (Tg) times up into a digital quantity and inputs it to the display drive section 40. 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. , and although not shown, the output is output only when the tightening is determined to be normal, and is digitally displayed on the display 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 logic circuit, for example, a microcomputer, which processes 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) (Ti), and uses the output signals thereof. The electromagnetic valves 43 and 44 that operate the lifting cylinder 14 and the driving means 15 are controlled to be energized and de-energized, and the transmission, switching, and stopping of high-speed and low-speed pulse trains supplied to the pulse motor drive circuit 45 are controlled. This switching is done when the temporary tightening is completed, and the stopping is done when the temporary tightening and final tightening are completed, or when the timer (Tc) times up and exceeds the machine time. It is done on a computer. 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.

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, at the same time the torque indicator 41 and judgment display section 37 are reset, and the timer (Ta) is reset.
(Tb) starts counting time. Power supply section 38
When the smoothing capacitor (Tb) completes charging and the timer (Tb) times up, the logic circuit 42 issues a command to supply and lower a high-speed pulse train drive pulse, the pulse motor 10 starts rotating at high speed, and the screw tightening machine main body 5 starts rotating. Descend and start temporary tightening work. 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 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 timer (Tc) times up during tightening. Then, a machine time-over signal is applied to the logic circuit 42, the power supply section, the timer (Ti), and the judgment display section 37, and the supply of the high-speed pulse train is stopped. At the same time, the operation command of the drive means 15 is issued and the screw tightening operation is completed. , a tightening failure is displayed. However, the indication of poor tightening is not made until the timer (Ti) times out. 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 an indication of poor tightening, indicates the start of returning the screw tightening machine body 5 to its original position, indicates a judgment display command based on the timer (Ti) time-up, or indicates whether tightening is normal when the timer (Ti) times up. Indicates the torque display command depending on the case. 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 up, and the comparator 27 issues a preliminary tightening completion signal,
As the timer (Td) starts counting time, 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 when the temporary tightening is completed, the catcher 7 will not move up after the catcher 7 has been raised. The condition is resolved and torque sensor 1
3 makes it possible to detect only the shaft torque that is purely involved in the tightening torque.

After the temporary tightening is completed, the screws become familiar with the workpiece and when the timer (Td) times up, a low-speed pulse train drive 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. Ru. Then, at the same time as the main tightening starts, two timers (Te) (Tf) start counting time. In this case, if the timer (Tc) times up even though the final tightening has not yet been completed due to an abnormality such as loose screws, the low speed The supply of the pulse train 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 message indicating that the final tightening is complete. Then, based on this signal, the supply of the low-speed pulse train from the logic circuit 42 is stopped, and the pulse motor 1
0 stops rotating. Also, at the same time, the timer (Tc)
(Tf) is reset and the 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 timer (Te) (Tf) times up. If the final tightening completion signal is issued before the timer (Te) times up or after the timer (Tf) times up, the screw may bite diagonally, skip the neck, etc. Since an abnormality has occurred, the screw tightening work is completed and a tightening failure is displayed. On the other hand, if the time when the final tightening completion signal is issued is after the timer (Te) times up and before the timer (Tf) times up, then the final tightening has been completed normally and the timer (Tg) times up. Wait for me, A.
The -D converter 39 is activated, and the torque value detected by the torque sensor 13 at the time when the timer (Tg) times up is converted into a digital value and inputted to the display drive section 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).
This judgment operation determines whether the torque value detected by the torque sensor 13 at the time after the timer (Tg) and (Th) and the A-D conversion time after the completion of the final tightening is higher or lower than the lower limit torque value of the setting device 26. It is determined how. 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, in a sense, this time is the same as the break-in time after completion of preliminary tightening and final tightening, but by making the time a little longer, stress relaxation, tightening torque becomes larger, or temperature increases. This takes into consideration the fact that the tightening torque tends to decrease due to the creep phenomenon promoted by. If the detected torque value is lower than the lower limit torque value of the setting device 26, the torque is ultimately insufficient, so wait for the timer (Ti) to time up, and then the judgment display section 37 will display a tightening failure indication based on the judgment display command. Do this. On the other hand, if the detected torque value is higher than the lower limit torque value of the setting device 26,
After waiting for the timer (Ti) to time up, the judgment display section 37 displays a good tightening condition according to the judgment display command, and the display 41 digitally displays the detected torque value held in the display drive section 40 according to the torque display command. Display each. 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 condition for starting the return of 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 final tightening time judgment 3
This is when an abnormal signal is issued from 5. According to this start condition, the power supply from the power supply unit 38 to the pulse motor drive circuit 45 is stopped, and at the same time, the timer (Ti) starts counting time. Eventually, the timer (Ti) times up and the power supply section 38
When the smoothing capacitor included in the smoothing capacitor is completely discharged and the voltage applied to the smoothing capacitor becomes zero, 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 1
4 moves back, and the screw tightening machine main body 5 rises together with the driver bit 11. At this time, the driver bit 11 that fits into the screw tightened to the workpiece is in a free state, so the driver bit 11 does not lift the workpiece as it rises, and the screw head is not damaged. , it can be smoothly removed from the screw. Further, when the timer (Ti) times up, a command is issued to the judgment display section 37 to display a judgment on whether the tightening is successful or not.
At this point, the judgment display section 37 indicates that the tightening is defective as described above.
Displays whether the tightening is good. If a torque display command is issued at this time, the detected torque value held in the display drive section 40 is displayed on the display 41 at the same time.

When the screw tightening machine main body 5 eventually returns to its original position due to the upward movement of the elevating cylinder 14, the timer (Ta) is reset, and the logic circuit 42 issues an operation release command to lower the drive means 15. The catcher 7 is lowered by the lowering of the drive means 15,
Returns to a state where new screws can be accepted. 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 up, the cycle over detecting section 33 displays a cycle time over display. Incidentally, the cycle time over display is performed even if the timer (Ta) times up 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. In the above embodiment, the time required to detect the shaft torque after a considerable amount of time has elapsed after the main tightening completion signal is issued is determined by the two timers (Tg) (Th) and the A-D converter 39. 3
This can also be done by a single timer that is set by the operator. In addition, although the example shows an example in which the present invention is applied to a single-shaft type screw tightening machine,
Of course, the present invention can also be applied to a multi-shaft type screw tightening machine. Furthermore, although the embodiment is limited to a pulse motor, a direct current motor can also provide similar effects.

As explained above, in the present invention, when the driver bit is raised after completion of main tightening, the pulse motor is held in an excited state by the voltage of the smoothing capacitor built in the power supply section of the pulse motor, and the driver bit is in a free state. As a means to prevent the driver bit's lifting cylinder from moving back before the power supply is reached, a timer is provided that counts the time at the same time as the power supply is cut off, and the time set for this timer is set to be longer than the discharge time of the smoothing capacitor. When the driver bit starts to rise, the transmission system including the driver bit is in a free state, and the driver bit does not lift the workpiece when the driver bit rises, and the screw head or the driver bit itself is not damaged. Not only can the screw be removed smoothly from the workpiece, there is no need to rotate the screw that has been tightened to the workpiece in the direction of further tightening, but only one additional timer is required.
There are advantages such as being able to provide an extremely inexpensive device.

[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.

Claims (1)

[Scope of Claims] 1. A pulse motor 10, a driver bit 11 which is rotationally driven by the pulse motor 10 to tighten a screw to a workpiece and can be raised and lowered by the operation of an elevating cylinder 14, and an axial torque of this driver bit 11. A final tightening comparator 28 is provided, which has a torque sensor 13 to detect the final tightening and outputs a final tightening completion signal when the shaft torque of the driver bit 11 reaches a predetermined final tightening torque. A control unit is provided that cuts off the supply of drive pulses to the pulse motor 10 and restrains the transmission shaft 12 of the pulse motor 10 with a stall torque while continuing power supply, and starts counting time in response to the final tightening completion signal. In an automatic screw tightening machine, a timer (Tg) is provided to shut off the power supply section in response to a time-up signal, and the elevating cylinder 14 is moved back after receiving this time-up signal. A timer (Ti) is provided which starts time counting by a signal and moves the lifting cylinder 14 backward by a time-up signal, and the set time of this timer (Ti) is set to be longer than the discharge time of the smoothing capacitor in the power supply unit 38. An automatic screw tightening machine characterized by being set to.