JPS5894939A - Automatic screw-fastening machine - Google Patents

Abstract

PURPOSE:To prevent a work and a driver bit from being broken, by prventing the driver bit from being raised until the time period for which electrical charge reaches a value at which a rotary shaft is made free, is elapsed, and by returning the driver bit to its original position after the lapse of the time period, thereby the screw is prevented from being further screwed into. CONSTITUTION:When a screw-fastening starting part 21 is actuated, a power supplying part 38 is operated for initiating the supply of power to a starter drive circuit 45, and timers Ta, Tb initiate time counts. A pulse motor 10 initiates a high speed rotation by an instruction from a logic circuit 42 so that provisional fastening is started. The final fastening is carried out when the screw gets to fit a work after the completion of the provisional fastening and the timer Td counts the time-up. Under the condition of starting the body being returned to its original position, a timer Ti counts the time-up, and therefore, a smoothing condenser contained in the power supplying part 38 discharges. The logic circuit 42 issues an instruction for lifting when the rotary shaft of the motor 10 is made free, and therefore, a lift cylinder 14 initiates the lift movement thereof.

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 against a workpiece, and a torque sensor that detects the shaft torque of the driver pin. The present invention relates to an automatic screw tightening machine configured to issue a final tightening completion signal when the shaft torsion of a driver bit reaches a predetermined final tightening torque value, and at the same time cut off the supply of drive pulses to a buffless motor.

This type of automatic screw tightening machine requires a driver pit.
A torque sensor detects the shaft torque of
The torque value is compared with a predetermined final tightening torque value set on a torque setting device or the like, and torque control is performed by controlling the drive pulse to the motor. Therefore, when the shaft torque of the driver bit r reaches the final tightening torque value, the drive pass to the pulse motor is stopped at 11, the driver bit is stopped, and the stop torque I is restrained. At the same time as cutting off the power supply from the power supply section to the buffless motor drive circuit, the driver bit is raised and returned to its original position. However, since the pulse motor itself requires a relatively stable supply voltage and a relatively large current, the power supply section uses a relatively large capacitor, and this capacitor affects the pulse motor drive circuit. Even if the power supply is cut off, it takes time for the charge stored in the capacitor to be discharged, and due to the voltage drop caused by this discharge transient charge, the pulse motor is still in an excited state, so the driver bit will not reach a certain torque. is in a restrained state. This certain measurement means that if the discharge transient charge is close to the charge during charging, it is close to the stall torque, and if it is close to the charge during discharge, it is close to the free state. Therefore, if the driver bit is raised and returned in this uncertain transient state of restraint, the driver bit will rise with the driver bit and the screw screwed into the workpiece firmly engaged, and at this time the screw will slightly tighten. When screwed in, the shaft Fμ may rise above the set final tightening torque value, or the screw head or workpiece may be damaged, or the driver bit may be damaged.

The present invention aims to eliminate the above-mentioned drawbacks, and embodiments thereof will be described below with reference to the drawings. Figure 11g1 shows a stationary single-axis automatic screw tightening machine as an example of an automatic screw tightening machine. A rod (4) is inserted through the rod (41) so as to be slidable up and down.A @N member (61) for attaching the screw tightening machine main body (5) is inserted into the rod (41) so as to be slidable up and down. A tension spring (to) is connected.Also.

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, there is a catcher (
A support plate (8) supporting the rod (7) is inserted freely and is received by a lug 1191V screwed into the lower end of the rod rod. The net TV #me machine main body (5) includes a pulse motor tIO, a driver bit 01) and a rotational drive source [I
A transmission shaft QZ that transmits rotational power from the driver bit αB to the driver bit αB, and the transmission shaft α2 is provided with a torque sensor Q3 that detects the axis t/I/r of the driver bit. Moreover, this screw tightening machine main body (5) is supported by V-? The vertical movement of the vertical lift cylinder 1141, which is configured to be able to move vertically by the vertical cylinder I provided at +21, is controlled by the catcher (
7), the catcher 171 also moves up and down along with the screw tightening machine body (5), but the amount of descent is determined by the rod (5).
4) The upper end and the upper arm part 13) are regulated by the catcher (7), which can be locked to a nut (16a) provided at the tip of the rod αG of the cylinder serving as the driving means a9. .

The operation of the drive means 05 allows for an upward movement independently of the lift valve t. Although not shown, there is a switch for confirming the return to the original position, such as a limit switch, which is turned on when the screw tightening machine body (51) has risen and returned to the original position. (14° drive means (+9 is controlled by the circuit shown in Figure 1!2, and is designed to perform automatic screw tightening operation.

In Figure 2, (2) is the screw tightening start part, (support) is Fμ
1 is a puffer amplifier that amplifies the detection signal of sensor α3, 1 is a calibration that performs correction gain correction of the detection signal, (2! ■ is the setting device with the final tightening value set, and ■ is the setting device with the lower limit meter set to the final minimum required value for product judgment after final tightening. For each of these setting devices @~ω, for example, a 10-turn potentiometer is used.
A is a comparator that compares the detected lv value and the temporary tightening value set in the setting device @, and a is the detection value and the actual tightening value set in the setting device e. The other is a comparator that compares the detected torque value with the lower limit torque value set in the setting device □□□. ■ is the reset part for poor tightening, and Gu is the limit meter switch for confirming the return of the screw tightening machine to its original position.

(to) is the cycle time over reset section.

Here, the cycle time refers to the time required for one screw tightening when the screw tightening is performed normally. Therefore, if screw tightening takes longer than this cycle time, it means that there is an abnormality on the screw tightening machine side. (Ta)~σC)
is a timer, and timer σa) is set to the cycle time.

The timer (Tb) is set to the charging completion time.

The charging completion time here refers to the time from when the flat capacitor of the power supply unit (described later) that supplies power to the pulse motor starts charging in response to the screw tightening start signal until the charging is completed. (re
) is set to machine time. Machine time refers to the time from the start of tightening force to the completion of wood 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 a screw is being tightened without a screw or whether the screw is loose or not. This is the time that can be used as a guideline to determine whether the screw or workpiece is normal or abnormal. 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 up to the time of completion, the transmission efficiency, the screw This is the time taken into account the transmission delay, etc. until transmission.・0 This running-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 running-in is the time detected at that time. The shaft torque is equal to the shaft torque [lv], and tends to be different from the shaft torque when the final tightening is completed.

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. Due to the effects of the body's unique characteristics, the tightening of the screw gradually changes and takes time to stabilize. Therefore, in such cases, it is necessary to lengthen the break-in time. However, the timer σ for setting the break-in time
Due to the characteristics of the pulse motor that rotates the driver pitch meter, the minimum time in d) may rotate by one pulse, so it should be taken into consideration so that it is at least the time equivalent to this one pulse. .

The timers (Te) and (Tf') each count the time at the same time as the final tightening starts. However, the set time of one of the timers σθ) is
Adjust the setting time of the other timer σ0 to the minimum time required for final tightening when no tightening defects have occurred, and adjust the setting time of the other timer σ0 to the maximum required time for final tightening when no tightening defects have occurred. The minimum and maximum required time for final tightening in the case where no such tightening defects occur can be determined empirically. usually.

Standard tightening time T8 by tightening many screws under the same conditions
(average value) and standard deviation f are determined, T9-36 is set as the minimum required time, and T6+a/ is 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 TS±3t. Of course, the minimum time and the maximum time can be set to T894 (, 51'J). The time has the same meaning as the break-in time after completion of preliminary tightening described above.However, due to the characteristics of the pulse motor, even after final tightening is completed, it may rotate for one extra pulse, so the minimum setting of the timer crN The time corresponds to this 1 pulse.The timer σh) counts the time based on the conversion completion signal of the A-D converter (described later), which starts conversion at the time up of the timer (T). Starting time, the time-up will be considerably slower than when the final tightening is completed.

When this timer σh) times up, the final tightening Fl
A determination is made instantaneously whether the value is higher or lower than the value set by the Lref lower limit meter setter (■).

It is set to the time required for the charge accumulated in the smoothing capacitor to discharge after the supply is cut off. As long as electric charge is accumulated in the smoothing capacitor, the pulse motor is in an excited state and stops [because it is restrained by the loop, when the screw tightening machine body 15) is moved upward in that 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 CI'i), it is possible to lift the screw tightening machine body (51) only after the excitation of the pulse motor is released and the rotating shaft becomes free. Since the timer (Ti) starts counting time in response to the time-up signal of the timer (Th), at the time the timer (Th) times up, the rotating shaft of the pulse motor is restrained by the stall torque, and the lower limit determination section described below Detection by the country is completed instantly. Therefore, the tightening torque of the screw at the time when the timer σh) times up can be detected by the torque sensor 03, and the lower limit determining section □□□ can make a final determination as to whether the screw has been tightened.

(to) is the CYC M time over detection section, and the timer (Ta
) times up, it displays CYC V time over and issues a signal to the outside. (Incorporated) is a machine time over detection section which issues a machine time over signal when the timer σC) times out. 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, pulse motor a
The supply of the pulse train to the drive unit a is stopped, and a drive command for the drive unit a 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 due to 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, the two timers (
're) It is determined that the tightening is defective based on σ0, but it is meaningless to keep the pulse motor running until the determination is made, and it is a waste of electricity, so it is possible to eliminate the meaningless state as soon as possible. The decision was made to issue a machine time-over signal to end the screw tightening work. The time required for final tightening of the can is determined by the timer (To
) and the time set in timer CI'f).
To) is detected when timer Crh) times up)
The lower limit determination unit, which determines whether 71/I is larger or smaller than the 1-lux value set in the lower limit F/I/R setting device ■, is configured to perform each of the above-mentioned determinations. This is a judgment display unit that displays whether the tightening is good or bad based on signals from the Bc151GBl and the time-over detection unit □□□. This judgment display cylinder does not perform a display operation unless the timer O1) times up.

(To) is a power supply section for supplying power to the pulse motor. When the start section □□□ operates, it starts supplying power and the timer ('['h) times up.

Alternatively, when the machine time over detection section □□□ or the final tightening time determination section (to) issues a detection signal, power supply is stopped. cll is a double integral type A-D converter that is resistant to noise, and converts the detected value of the F!lex sensor a3 at the time when the timer (To times up) into a digital quantity and inputs it to the display drive unit. The display drive section (G) is synchronized so that the display timing is the same as that of the above-mentioned foot display section (3), so the display section (G) judges the digital amount inputted from the A-D converter (support). Although it is not shown in the figure, it is output only when the tightening is determined to be normal and is digitally displayed on the display f411.However, the displayed value is determined by the timer described above. 0g) is the detected F/I/value of the )/l/x sensor 113 at the time of time-up. +42 is a logic circuit for processing signals such as the comparison output of the preliminary tightening comparator cylinder and the output of the timer crb (Td) The solenoid valve (circuit) that operates the drive means rotor is energized and de-energized, and also controls the transmission, switching, and stopping of the high-speed and low-speed pulse motor drive circuits (c) that are supplied to the pulse motor drive circuit (c). This switching is done when the temporary tightening is completed, and the stop is performed when the temporary tightening and final tightening are completed, or when the timer (Tc) times out and the machine time exceeds. The transmission of the train is performed by a microcomputer.High-speed pulses refer to pulses having a frequency higher than the self-starting frequency of the pulse motor αG, and low-speed pulses refer to pulses lower than the self-starting frequency of the pulse motor αG.

Next, the automatic screw tightening operation based on the above configuration will be explained according to the flowchart shown in FIG. When the screw tightening start section ell operates, the power supply section (to) operates and starts supplying power to the pulse motor drive circuit (c), and at the same time the % FA/re indicator (41) and the judgment display section (to) operate. ) is reset, and the timer (Ta') Crb) starts counting time. When the smoothing capacitor of the power supply section ■ completes charging and the timer (lrb) times up, the logic circuit issues a command to supply and lower a high-speed pulse train of drive pulses, causing the P/L/N motor [1+1 to rotate at high speed. At the same time, the screw tightening machine main body 15) descends to start the temporary tightening work. Also, at this time, the simultaneous timer ('1'Q) starts counting time. If there is no abnormality in the temporary tightening work, the timer (I'c) 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, , timer Cr) times up during temporary tightening. Then, a machine time-over signal is applied to the logic circuit, power supply section, timer σ1), and judgment display section (9), and the supply of the high-speed pulse train is stopped, and at the same time, the drive means port S
operation command, completion of screw tightening work, and indication of poor tightening. However, the indication of poor tightening is made only after the timer (cri) has timed up.The reason why we decided to issue an operation command for the drive means 05 using this man-time over signal is that this command causes the catcher (7) to By raising the screws in the catcher (71) and discharging the screws in the catcher (71), the purpose is to eliminate the situation where there are two screws in the catcher (7) during the next screw tightening operation. (■ indicates the start of the screw tightening machine body (5) returning to its original position, 0 indicates the timer 01)
(time-up of timer σ1)) indicates the judgment display command, and (2) indicates the display command when the tightening was normal when the timer σ1) time-up [/I/]. When the initial position return operation is started, as shown in FIG. By the time the time is up, the lux sensor detects the lv value.
When the pre-tightening torque value is reached and a pre-tightening completion signal is issued from the comparator cylinder, timer σ starts counting time.

The supply of high-speed pulse trains from the logic circuit has stopped.

At the same time, a drive means activation command is issued. When the supply of the pulse train is stopped, the pulse motor 09 stops rotating, and the drive means 09 is actuated by the drive means operation command. Drive means o
! Since the catcher (7) is raised independently by the operation of 9, even if the head of the screw is held or caught in the catcher when the temporary tightening is completed, after the catcher 17) has been raised, The condition is resolved and t
The lux sensor A can be used to detect only the axial torque that is purely applied to the tightening torque.

After the temporary tightening is completed, the screws will fit into the workpiece and the timer cIld)
When the time has elapsed, a low-speed pulse train drive pulse is emitted from the logic circuit, and final tightening is performed while rotating the pulse motor 0α at a low speed below the self-starting frequency. Then, at the same time as the final tightening starts, two timers (To) C0 start counting time.

In this case, if the timer σC) times out even though the final tightening has not yet been completed due to an abnormality such as loose screws, the pulse motor (low-speed The supply of the pulse train is stopped and the screw tightening work ends at the same time.

Inadequate tightening display ■ will be displayed.

On the other hand, there is no abnormality in screwing, and torque sensor a3 detects F.
When the rect value reaches the final tightening value of the setting device O, the comparator outputs a final tightening completion signal.

Then, based on this signal, the supply of the low-speed pulse train from Giichi Logic Circuit Co., Ltd. is stopped, and the pulse motor (IG) stops rotating counterclockwise.At the same time, the timer σc)C1rf') is reset [and the timer Crg) starts counting time.

In this case, the time when the final tightening completion signal is issued is the time when the zero final tightening completion signal is issued, which determines whether the final tightening completion signal is issued before or after the timer (re)C0 times up. If the time has elapsed before the timer ('rf) has timed up or after the timer ('rf) has timed up, the screw has some kind of abnormality such as diagonal bite or neck skipping, so it is necessary to tighten the screw. The completion and poor tightening display ■ will be displayed. On the other hand, the time when the final tightening completion signal is issued is after the timer σe) has timed up and the timer σe) has expired.
If it is before the time-up of 1, the final tightening has been completed normally, so wait for the timer (7g) to time-up, start the A-D conversion, and set the timing when the timer CI'g) reaches the time-up of 1-. [Detection of jv xensa α3)/
The reflex value is digitally converted and input to the display driver (a). The display drive section holds this input signal at -I, and operates to display when the tightening is normal at the same timing as the judgment display section (To).

The A/D converter (to) operates and the timer ('I'h) starts counting time at the same time as it issues a conversion completion signal. In response to the time-up signal (d) of the timer (Crh), the lower limit determining section (2) performs a determining operation. With this judgment operation,
After the completion of the main tightening, check whether the torque sensor a3 detection value at the time after the timer criIO and (Th) time and the A-D conversion time is higher or lower than the lower limit [/L/ value of the setting device]. It is determined.

The reason why we selected the detected torque value after a considerable amount of time has passed after the completion of the final tightening as the subject of judgment is because we believe that this is equivalent to an extension of the break-in time after the completion of the final tightening. Therefore, in a sense, this time is the same as the break-in time after completion of temporary tightening and final tightening, but by making it a little longer by 1 hour, it will be possible to further relieve stress and reduce tightening pressure. This is in consideration of the fact that the Fjv tends to decrease due to the creep phenomenon, which is promoted by an increase in Fjv or a rise in temperature. If the detected Flv value is lower than the lower limit 11 rec value of the setter ■, the final result is [lref is insufficient, so wait for the timer ('ri) to time up and make a judgment based on the judgment display command ■. Display command indicates poor tightening. On the other hand, if the detected torque value is higher than the lower limit torque value of the setting device ■, wait for the timer ('I'i) to time up, and then the judgment display section ■ will tighten according to the judgment display command ■. The display +411 digitally displays the detected torque value held in the display drive unit by the metered torque display command (2). Furthermore.

When the lower limit determination section (to) makes the above determination, the screw tightening work is completed regardless of whether the determination result is good or bad.

Next, the operation of returning the screw tightening machine main body (5) to its original position will be explained based on the flowchart shown in FIG. Screw tightening machine body (
As mentioned above, the condition for starting 0 for the return to the original position of 51 is when the timer Crh) times up, or when the timer σC)
This is when the machine time exceeds due to time-up, or when an abnormal signal is issued from the final tightening time judgment (reach). According to this start condition, the power supply from the power supply section to the pulse motor drive circuit is stopped, and at the same time, the timer CI'i) starts counting time. Eventually, the timer ('
When ri) times up, the smoothing capacitor included in the power supply section (to) is completely discharged, the voltage applied to the smoothing capacitor becomes zero, and the rotation axis of the pulse motor O becomes free. A rising command is issued and the lifting cylinder a4 starts to move upward. In addition, the judgment display section (support) is
At this time, a command is issued to display whether the tightening is successful or not, and at this time, the cutting judgment display section displays the above-mentioned insufficient tightening or good tightening. At this time, if the torque display command (2) has been issued, the detected torque value held in the display drive section (1) is displayed on the display 111 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 α4, the timer (Ta) is reset, and the logic circuit Yu issues a deactivation command to lower the drive means port 9. As the drive means 05 descends, the catcher (7) descends.

Returns to a state where new screws can be accepted. in this case,
Even if the logic circuit issues a lift command, the screw tightening machine body (
5) does not return to the original position, and therefore the timer cra) times up, the cycle M over detection section (to) displays a cycle time over display. The cycle time over display cannot be performed even if the timer αa) 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. helmet, in the above example.

The time required for detecting shaft torsion after a considerable amount of time has elapsed after the final tightening completion signal is issued is set by three parties: two timers σρ (Th) and an A-D converter ■. However, it can also be done by a single timer. Also,
Although the embodiment shows an example 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. Further, in the embodiment, a pulse motor is used, but a direct current motor can also provide the same effect.As explained above, the automatic screw tightening machine according to the present invention has a
At the same time as the final tightening completion signal is issued, the supply of the vibration path to the pulse motor is cut off, its rotating shaft is stopped, and the motor is restrained to a standstill.

In general, since the configuration is such that the driver pin is raised and returned only after a predetermined period of time has elapsed after the power supply to the pulse motor drive circuit is cut off and the rotating shaft is in the IJ - state, the driver pin is not raised and returned to its original state. The final tightening is completed without having to screw in the screws that were not inserted further! This method has the advantage that not only can the torque value be set to match the actual tightening torque value, but there is no possibility of damage to the screw head or workpiece, or damage to the screw head or workpiece.

[Brief explanation of drawings]

Fig. 1 is a side view of an automatic screw tightening machine showing one embodiment of the present invention. Figure 2 is the electrical circuit diagram of the screw tightening machine, and Figure 3 (a)
Jl/"j is a flow chart explaining the screw tightening operation of the screw tightening machine, and FIG. 4 is a flow chart t explaining the return operation of the screw tightening machine to its original position. αl...Pulse motor, αU −...Driver bit. α3...Torque sensor. Patent applicant Nitto Seiko Co., Ltd.

Claims (1)

[Claims] A pulse motor, a driver pin that is rotationally driven by the motor to tighten a screw to a workpiece, and a lux sensor that detects the shaft torque of the driver bit, and the shaft of the driver bit is set at a predetermined position. In an automatic screw tightening machine that is configured to issue a final tightening completion signal when the final tightening value is reached, and at the same time cut off the supply of drive pulses to the pulse motor, when a single tightening completion signal is issued, the final tightening completion signal is issued. When the power supply from the power supply unit, which is the power supply source, to the pulse motor drive circuit is cut off, the electric charge stored in the smoothing capacitor in the power supply unit starts discharging, and at least the rotating shaft becomes free. An automatic screw tightening machine characterized in that the driver pin is raised and returned to its original position only after a period of time has elapsed until one electric charge is reached.