JPS6325896B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention emits a temporary tightening completion signal when the shaft torque of the driver bit reaches a predetermined temporary tightening torque,
This invention relates to an automatic screw tightening machine that performs final tightening after that point. Temporary tightening here means temporary tightening of a screw to a workpiece. Therefore, the screw may not be completely pushed out from the catcher during the temporary tightening stage. Therefore, even if the screw tightening torque has not reached the temporary tightening torque, it may be detected that the temporary tightening torque has been reached because the screw head is held in the catcher. Even if the screw is not tightened to the workpiece at all, it may be detected that the temporary tightening torque has been reached because the screw head is caught in the catcher. In such a case, if the final tightening is performed as it is, accurate torque control will not be possible, and problems such as diagonal biting of the screws and floating of the screws will occur.

The present invention provides a novel means that can eliminate such adverse effects at the stage of completion of temporary tightening, and the gist thereof is as follows:
In an automatic screw tightening machine that issues a temporary tightening completion signal when the shaft torque of the driver bit reaches a predetermined temporary tightening torque, and then performs the final tightening from that point on,
The gist of the present invention is to provide a driving means for moving a catcher holding a screw upwardly and independently from the driver bit, and to operate the means based on a preliminary tightening completion signal after the preliminary tightening is completed and before starting the final tightening. .

Next, one embodiment of the present invention will be described based on the drawings. Fig. 1 shows a stationary single-shaft type automatic screw driver as an example of an automatic screw driver. A rod 4 is inserted into the holder so as to be slidable up and down. An attachment member 6 for attaching a screw tightening machine 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 driver bit 1 as a rotational drive source, for example.
1 and a transmission shaft 12 for transmitting rotational power, and the transmission shaft 12 is provided with a torque sensor 13 for detecting 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 operation of the lifting cylinder 14 is carried out by the catcher 7 via the rod 4.
The catcher 7 also moves up and down together with the screw tightening machine main body 5, but the amount of descent is the same as that of the rod 4.
It is regulated by the upper end of and the upper arm part 3. Further, the catcher 7 is 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. . Although not shown, a switch such as a limit switch that is turned on when the screw tightening machine main body 5 has been raised and returned to the original position is provided to confirm the return to the original position.

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 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. 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 24 to 2
6 is a 10-turn potentiometer, for example. A first comparator 27 compares the torque value detected by the torque sensor 13 with the temporary tightening torque value set in the first setting device 24 and issues a temporary tightening completion signal.
8 is a second comparator that compares the detected torque value and the main tightening torque value set in the second setter 25 and issues a main tightening completion signal; 29 is a set between the detected torque value and the third setter 26; This is a third comparator that compares the lower limit torque value. 30 is a reset part due to poor tightening; 3
Reference numeral 1 indicates a limit switch for confirming return of the main body of the screw tightening machine to its original position, and reference numeral 32 indicates 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 the smoothing capacitor used in the power supply section 38 that supplies power to the pulse motor 10 starts charging in response to the screw tightening start signal until the charging is completed. This timer Tb 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 refers to the time it takes to complete the final tightening when screws are normally tightened.
While the cycle time was used as a guide to check 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 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 is the initial detection error due to the material or abnormality of the workpiece or screw that was included in the shaft torque detected by the torque sensor 13 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 become familiar with 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 a case, it is necessary to lengthen the break-in time. However, there is a timer for setting the break-in time.
When a pulse motor is used as a rotational drive source, the minimum time of Td is 1 due to the characteristics of the pulse motor.
Since there is a case where the rotation is made for an extra pulse, the time is taken into consideration so that it is longer than the time corresponding to one pulse. The timer Te is set to the minimum required time from the start of the final tightening to the completion in a normal case where the screw does not bite diagonally or is floating, and the timer Tf is set to the minimum time required from the start to the completion of the final tightening in the same case. is set to the maximum required time. This setting time is the standard final tightening time Ts (average value) when tightening many screws under the same conditions.
and the standard deviation σ can be determined from this Ts and σ. Normal timer Te is Ts−3σ
, timer Tf is set to Ts+3σ. This 2
The two timers Te and Tf determine whether there is any abnormality in the tightening condition from the start of the final tightening to the completion of the final tightening. In other words, if the final tightening time is abnormally short and the final tightening is completed before the timer Te times up, it can be determined that the screw is sticking diagonally or is floating, and conversely, the final tightening time is is abnormally long and the timer
If the final tightening is not completed even after Tf has timed out, it can be determined that the screw has skipped its neck or the like. The timer Tg is set to the break-in time after the main 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, it may rotate one pulse more even after the final tightening is completed, so the timer described above may rotate.
The minimum setting time of Tg is considered to be a time corresponding to one pulse. Timer Th
starts counting time at the conversion completion signal of the 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. 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 38 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 when the screw tightening machine body 5 moves upward in this state, torque is applied to the screw. In this situation, the driver bit may 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. However, if a motor other than a pulse motor is used, this timer Ti is unnecessary.

33 is a cycle time over detection section which, when 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. 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, and 36 is the detected torque when time-Th is up. a lower limit determination unit 37 that determines whether the torque value 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 display section 37 does not perform a display operation unless the timer Ti times up. Reference numeral 38 denotes a supply unit for supplying power to the pulse motor 10, which starts supplying power when the start unit 21 operates, and when the timer Th times up or the machine time-over detection unit 34
Alternatively, when the main tightening time determination section 35 issues a detection signal, power supply is stopped. 39 is strong against noise 2
A double integral type AD converter converts the detected torque value when the timer Tg times up into a digital quantity and inputs it to the display drive section 40. here,
The detected torque value is A without going through the peak hold circuit.
- This is because the input is directly to the D converter 39, so in the case of a pulse motor, the rotating shaft under excitation/stopped pulse supply is in a stopped rotation state and is restrained by stall torque. It is. Therefore,
In the case of motors other than pulse motors, the rotating shaft becomes free when rotation is stopped, so it is necessary to 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 digital amount inputted from the converter 39 is output at the same timing as the display on the judgment display section 37, and is digitally displayed on the display 41. 42 is the output of the first comparator 27 and the second comparator 28, the timer Tb,
This is a logic circuit, such as a microcomputer, that processes signals such as Td and Ti outputs. After receiving the signal from the screw tightening start section 21, this logic circuit 42 receives the output of the timer Tb.
A high-speed pulse train supply command is issued to the pulse motor drive circuit 45 to rotate the pulse motor 10, and a command to lower the lifting cylinder 14 is issued to energize the solenoid valve 43 to supply air to the lifting cylinder 14 from a fixed direction. It is configured. The logic circuit 42 issues a high-speed pulse train stop command in response to the temporary tightening completion signal from the first comparator 27, and then, upon receiving the output of the timer Td, commands the pulse motor drive circuit 45 to supply a low-speed pulse train. It is configured to emit a signal and switch between high speed and low speed. Further, the logic circuit 42 issues a high-speed pulse train stop command to the pulse motor drive circuit 45 based on the output of the timer Tc or the temporary tightening completion signal from the first comparator 27, and then energizes the solenoid valve 44 to stop the command. While operating the actuator 15 to supply air from a certain direction to the drive means 15, the solenoid valve 44 is de-energized in response to an output signal from the limit switch 31 for confirming the return of the screw tightening machine body 5 to its original position. is configured to reverse the air supply direction. Moreover, when this logic circuit 42 receives the output of the timer Tc or the timer Ti, it de-energizes the solenoid valve 43, reverses the air supply direction, and returns the lifting cylinder 14. 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 a high speed, and when a low speed pulse is applied, the pulse motor 10 rotates at a low speed. The reason why the pulse motor 10 is rotated at high speed during the temporary tightening stage is to shorten the screw tightening time, and the reason why the pulse motor 10 is rotated at low speed during the final tightening stage is to ensure high precision. This is to enable torque control.

Next, the automatic screw tightening operation with the above configuration will be explained according to the flowchart shown in FIG. When the start section 21 operates, the power supply section 38 operates,
At the same time as starting power supply to the pulse motor drive circuit 45, the torque indicator 41 and the judgment display section 37
is reset, and timers Ta and Tb start counting time. When the smoothing capacitor of the power supply unit 38 has completed charging and the timer Tb has timed out, a high-speed pulse train supply command is issued from the logic circuit 42 to the pulse motor drive circuit 45, the pulse motor 10 rotates, and the driver bit 11 rotates at high speed. do. At the same time, the logic circuit 42 issues a command to lower the lifting cylinder 14, energizes the solenoid valve 43, supplies air to the lifting cylinder 14 from a certain direction, and lowers the rod, so that the screw tightening machine holding the driver bit 11 The main body 5 is lowered and the temporary tightening work is started. Also, the timer Tc starts counting time at the same time and detects a temporary tightening abnormality.

For example, if this timer Tc is set to
If there is an abnormality such as a screw being twisted inside, the shaft torque of the driver bit 11 does not reach the temporary tightening torque value during temporary tightening, and the timer Tc times up. Therefore, the logic circuit 42 issues a high-speed pulse train stop command to the pulse motor drive circuit 45 to stop the pulse motor 10, and at the same time, the solenoid valve 44 is energized to supply air to the drive means 15 from a certain direction, thereby causing the drive means 15 to stop. Activate and catcher 7
is increased independently for driver bit 11. Therefore, the driver bit 11 protrudes from the catcher 7, and the screws retained in the catcher 7 are removed. After that, the logic circuit 12 waits for the timer Ti to time up, and the logic circuit 12 operates the lift cylinder 14.
A raising/lowering command is issued, and the screw tightening machine main body 5 returns to its original position in accordance with an operation for returning the screw tightening machine main body 5 to its original position, which will be described later. Further, in parallel with these operations, due to the time-up of the timer Tc, a signal instructing poor tightening is input to the determination display section 37, and the defective tightening is displayed. However, even if the signal is input to the judgment display section, the failure indication will not be made until the timer Ti times up. In the flowchart, indicates a signal indicating poor tightening, indicates the start of returning to the original position, and indicates a display command due to time-up of timer Ti.

On the other hand, there is no abnormality in the temporary tightening work, and the detected torque value of the torque sensor reaches the temporary tightening torque value of the first setting device 24 before the timer Tc times out, and the first comparator 27 issues a temporary tightening completion signal. Then, the timer Td starts counting time, and the supply of the high-speed pulse train from the logic circuit 42 is stopped.
At the same time, a drive 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 driving 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 pure tightening torque.

After the temporary tightening is completed, the screws will fit into the workpiece and the timer will start.
When Td times up, a low-speed pulse train supply 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. Also, at the same time as the main tightening starts, timers Tc and 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 screw looseness, the supply of the low-speed pulse train from the logic circuit 42 is stopped, the pulse motor 10 stops rotating, and the above-mentioned As in the case of defective temporary tightening, a defective tightening signal is issued and the operation of returning the screw tightening machine body 5 to its original position is started.

On the other hand, there is no problem with the screw, and the torque sensor 13
The detected torque value reaches the final tightening torque value of the second setter 25, and the second comparator 28 issues a final tightening completion signal. Based on this signal, the logic circuit 42
From then on, the supply of the low-speed pulse train is stopped, and the pulse motor 10 stops rotating. Also, at the same time the timer
Tc and Tf are reset, and timer Tg starts counting time. In this case, it is determined whether the final tightening state is normal or abnormal 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 the timer Te has timed up or after the timer Tf has timed up, the screw may bite diagonally or cause some kind of abnormality such as neck skipping. Therefore, as in the case of the temporary tightening failure described above, a tightening failure signal is issued, and the operation of returning the screw tightening machine main body 5 to its original position is started. On the other hand, if the time when the final tightening completion signal is issued is after timer Te has timed up and before timer Tf has timed up, there is no abnormality in the screw and the final tightening has been completed normally, so timer Tg times up. After that, the A/D converter 39 is activated, and the torque value detected by the torque sensor 13 at the time when the timer Tg times out 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 displays the judgment display section 3.
It operates to display at the same timing as 7.

The A/D converter 39 operates and outputs a conversion completion output, and at the same time, 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. By this judgment operation, the timers Tg and Th are set after the main tightening is completed.
It is determined whether the torque value detected by the torque sensor 13 at the time after the time and the AD 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 had passed after the completion of the main tightening as the subject of judgment, as we considered this to be equivalent to an extension of the break-in time after the completion of the main tightening, and used this as the final means of determining whether the tightening was successful. This is for Tosenga. Therefore, this time has the same meaning as the break-in time after completion of temporary tightening and final tightening, and by making the time a little longer, stress relaxation, tightening torque increases, 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 third setter 26, it means that the torque is insufficient, so wait until the timer Ti times up, and then the determination display section 37 displays a failure display in accordance with the display command.

On the other hand, if the detected torque value is higher than the lower limit torque value of the third setter 26, wait for the timer Ti to time up, and in response to the display command, the judgment display section 37 will display a display indicating that the tightening is good. A display 41 digitally displays the detected torque value held in the section 40. Furthermore, once the lower limit determination unit 36 makes the above determination, the screw tightening operation is finally completed, so whether the determination result is good or bad, the operation of returning the screw tightening machine body 5 to its original position is started. It will be done.

Next, the operation of returning the screw tightening machine main body 5 to its original position will be explained based on the flowchart of FIG. 4. As mentioned above, the conditions for starting the return of the screw tightening machine 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 signal is generated from the main tightening time determination section. It's time to do 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 the timer Ti
starts counting time. Eventually, when the timer Ti times up and the rotation axis of the pulse motor 10 becomes free, the logic circuit 42 activates the lift cylinder 14.
issues a lift command, de-energizes the solenoid valve 43 and reverses the air supply direction of the lifting cylinder 14;
The lifting cylinder 14 is returned to its original position, and the screw tightening machine main body 5 is raised and returned to its original position. When the limit switch 31 for confirming return to the original position outputs an output due to the upward return of the screw tightening machine body 5, the logic circuit 42 activates the solenoid valve 44.
is de-energized, the direction of air supply to the drive means 15 is reversed, and this is returned to the catcher 7.
Return to the original position and prepare for the next work.

Further, when the timer Ti times up, a command is issued to the judgment display section 37 to display a tightening pass/fail judgment, and at this point, the judgment display section 37
displays the above-mentioned poor or good tightening. At the same time, the detected torque value held in the display drive section 40 is displayed on the display 41. In this case, even if the logic circuit 42 issues an ascending 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 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 up at any point after the screw tightening start section 21 is activated and 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 performed.

Although the present embodiment has been described with respect to a stationary single-shaft type automatic screwdriver, similar effects can be obtained with a stationary multi-shaft type automatic screwdriver.

As explained above, the automatic screw tightening machine according to the present invention is provided with a drive means for lifting the catcher that holds the screw separately and independently from the driver bit, and the drive means is activated after the temporary tightening is completed based on the temporary tightening completion signal. Since it is configured to operate before the start of tightening, it has the following effects. That is, if the tightening torque of the screw has not reached the temporary tightening torque, but it is detected that the screw head has reached the temporary tightening torque because the screw head is held in the catcher, the driving means Due to the upward movement of the catcher during operation, the screw head is released from being held, and subsequent final tightening can be performed purely while detecting the tightening torque of the screw. Therefore, highly accurate torque control is possible.
In addition, if the screw head is not tightened at all and reaches the temporary tightening torque due to the screw head being caught in the catcher, the catch will be resolved by the upward movement of the catcher by the operation of the drive means. and the screw is ejected. This prevents diagonal biting of the screws and screw floating, which tend to occur during the final tightening stage, and also prevents the screws from becoming stuck inside the catcher when tightening new screws. I have never known it to exist.

[Brief explanation of the drawing]

FIG. 1 is a side view of an automatic screw driver showing an embodiment of the present invention, FIG. 2 is an electric circuit diagram of the screw driver, and FIG.
Figures A, B, and C 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. 7... Catcher, 11... Driver bit, 15... Driving means.

Claims (1)

[Scope of Claims] 1. A lift cylinder 14 is provided which lowers the driver bit 11, which rotates in response to the rotation of the motor, and the catcher 7, which holds the screw on its moving path, to a predetermined position together, and the catcher 7 is moved by the driver. A driving means 15 is provided for upwardly moving the bit 11 separately from the bit 11, and a torque sensor 1 for detecting the shaft torque of the driver bit 11 is provided.
In addition, a first setting device 24 and a second setting device 25 are provided for setting the temporary tightening torque value and the main tightening torque value, respectively.
A first comparator 27 and a second comparator 2 compare the shaft torque of No. 1 with the temporary tightening torque value and the actual tightening torque value.
8 is provided, and when the shaft torque of the driver bit 11 reaches a predetermined temporary tightening torque value, a temporary tightening completion signal is issued from the first comparator 27, and from that point on, the final tightening is performed, and the shaft torque reaches the predetermined final tightening torque value. In an automatic screw tightening machine configured to issue a final tightening completion signal from a second comparator 28 and finish the screw tightening operation when a specified torque value is reached, an electromagnetic valve that operates an output of the first comparator 27 to actuate the drive means 15 is used. An automatic screw tightening machine characterized in that it is connected to a circuit for controlling energization and de-energization of 44, and is provided with means for independently raising the catcher 7 in response to a temporary tightening completion signal.