JPH0258068B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a drive stop control method for a power screw tightening device such as a nut line, and in particular, after the completion of tightening one screw pair, the next screw pair is stopped. The present invention relates to a drive stop control method for a power screw tightening device that repeatedly tightens a plurality of pairs of screws of the same type.

[Prior Art] A power screw tightening device such as Nutline tightens a pair of screws by rotationally driving a screw tightening tool using a rotary actuator such as a pneumatic rotary actuator or an electric motor. There is. When the drive of the rotary actuator is stopped, the power-powered screw tightening device stops the rotation of the screw tightening tool and finishes tightening the screw pair, but in reality, the rotating part of the power-powered screw tightening device Due to inertia, the screw fastener continues to rotate a little even after the rotary actuator is stopped, and tightens the screw pair. Therefore, in order to finish tightening a screw pair at a predetermined target tightening torque, the tightening torque must be adjusted to the predetermined target tightening torque, taking into account the increase in tightening torque due to overrun of the screw tightener as described above. When the tightening torque reaches the tightening torque obtained by subtracting the increase in tightening torque due to overrun from the applied torque, it is necessary to stop driving the rotary actuator.

[Problem to be solved by the invention] However, the amount of increase in tightening torque due to overrun of a screw fastener depends on variations in physical and mechanical properties such as friction coefficient, hardness, and elastic deformation rate between the screw and the pair. The amount of overrun of the screw fastener also changes due to variations in drive stop control of the rotary actuator, variations in rotational power loss in the reduction gear mechanism or joint between the rotary actuator and the screw fastener, etc. . Therefore, the tightening torque that should stop the drive of the rotary actuator, that is, the rotational drive stop torque, is a constant value obtained by subtracting the increase in tightening torque due to overrun of the screw fastener, which has been determined in advance through experiments, from the predetermined target tightening torque. Once the value of is fixed in advance, the value of the threaded pair will be adjusted according to variations in the physical and mechanical properties of the threaded pair, the drive stop control of the rotary actuator, and the rotational power loss in the reduction gear mechanism and joint. The tightening completion torque varies, and it is not possible to finish tightening a screw pair with a predetermined tightening torque.

The inventor of the present application has investigated variations in the physical and mechanical properties of a screw pair, the drive/stop control characteristics of the rotary actuator of a power screw tightening device, and the power loss in the power transmission section of a power screw tightening device. As a result of a detailed study of the phenomena of variation in the number of screws, it was found that these phenomena have a certain tendency over time due to changes in performance over time due to the manufacturing conditions of screw pairs and the usage environment of power-powered screw tightening equipment. I found out.

As mentioned above, the present invention focuses on the fact that variations change with a certain tendency over time, and by correcting the target drive stop torque to increase or decrease in response to changes in variations that occur over time, the present invention constantly It is an object of the present invention to provide a drive stop control method for a power screw tightening device that is improved so that tightening of a pair of screws can be completed with an appropriate tightening torque.

[Means for Solving the Problems] According to the present invention, this object is a power-driven method that repeatedly tightens a plurality of screw pairs of the same type to the next screw pair after completion of tightening one screw pair. A drive stop control method for a screw tightening device that measures the tightening torque during tightening and stops the screw tightening device when the tightening torque reaches the target drive stop torque within a predetermined time after the start of tightening. stop the drive, measure the tightening completion torque after the completion of tightening, calculate the deviation between the average value of the tightening completion torque over a predetermined number of times in the past and the predetermined target tightening torque, and calculate the deviation. The next target drive stop torque is corrected to be reduced or increased depending on the magnitude and sign of This is achieved by a drive stop control method for a power screw tightening device, which is characterized by stopping the drive and not correcting the target drive stop torque.

[Operation of the invention] If the physical and mechanical properties of each screw pair are constant and the operating conditions of the powered screw tightening device do not change, the amount of increase in tightening torque due to overrun of the screw tightener For example, as shown by the solid line A in Fig. 4, the tightening torque T reaches the target drive stop torque Tc within a predetermined time t ₁ to _{t 2} after the start of tightening. If the drive of the tightening device is stopped at this time, the tightening of the paired screws will continue due to overrun of the screw tightener until the tightening torque reaches the tightening end torque T _F which is substantially equal to the target tightening torque To. As a result, each screw pair can be tightened with a torque substantially equal to the target tightening torque To.

However, if the physical and mechanical properties of each screw pair change or the operating conditions of the screw tightening device change, the amount of increase in tightening torque due to overrun of the screw tightening tool will also change. The tightening torque T reaches the target drive stop torque within a predetermined time t ₁ to _{t 2} after the start.
Even if the drive of the tightening device is stopped when Tc is reached, the target tightening torque T
It cannot be tightened with a torque equal to . For example, as shown by solid line B in Figure 4,
If the tightening torque reaches the target drive stop torque relatively early within the predetermined time _t1 to _t2 , the tightening end torque T _F will be higher than the target tightening torque To, and conversely As shown by the solid line C in Fig. 4, if the tightening torque reaches the target drive stop torque at a relatively late point within the predetermined time _t1 to _t2 , the tightening is completed. The torque T _F has a value lower than the target tightening torque To.

According to the method of the present invention, the deviation between the average value of the tightening end torque over a predetermined number of times in the past and the target tightening torque is calculated, and the next target drive stop is determined depending on the magnitude and sign of the deviation. The torque is corrected to be reduced or increased, so that the amount of increase in tightening torque due to overrun of the screw fastener is reduced or increased, respectively, depending on the magnitude and sign of the deviation. Therefore, even if the physical and mechanical properties of the screw pair or the operating conditions of the screw tightening device change,
Each screw pair can be tightened with a torque substantially equal to the target tightening torque.

For example, when the tightening torque changes as shown by the solid line B in Fig. 4, the target drive stop torque is corrected to be reduced as shown by Tc' in Fig. 4, and the drive of the screw fastener is stopped. By performing this at an early stage, the amount of increase in tightening torque due to overrun of the screw fastener is reduced, so the tightening torque after the drive of the screw fastener is stopped is at one point in Figure 4. The torque changes as shown by the chain line, and finally becomes approximately equal to the target tightening torque To. Conversely, when the tightening torque changes as shown by the solid line C in Fig. 4, the target driving and stopping torque is corrected to increase as shown by Tc'' in Fig. 4. By stopping the drive at a relatively late stage, the amount of increase in tightening torque due to overrun of the screw fastener is increased, so the tightening torque after the drive of the screw fastener is stopped is The tightening torque changes as shown by the dashed line in FIG. 4, and in this case as well, it ultimately becomes approximately equal to the target tightening torque To.

Furthermore, according to the method of the present invention, the tightening torque T changes as shown by the broken line D or E in FIG. Tightening torque T within ₁ ~ t ₂
When does not reach the target drive stop torque Tc,
Since the next target drive stop torque is not corrected, it is reliably avoided that the target drive stop torque is corrected based on an abnormal tightening result.

The invention will now be described in detail by way of example embodiments with reference to the accompanying drawings.

[Example] FIG. 1 is a schematic configuration diagram showing a power screw tightening device and its control device used to implement the drive stop control method according to the present invention. In the figure, reference numeral 1 indicates a power screw tightening device, which is, for example, a nut runner, and includes a pneumatic rotary actuator 2, a reduction gear device 3, a joint 4, and a screw such as a wrench. The screw fastener 5 is adapted to be rotationally driven by the pneumatic rotary actuator 2. The pneumatic rotary actuator 2 is rotated by being selectively supplied with air pressure from a pneumatic source (not shown) via an electromagnetic switching valve 6.

The electromagnetic switching valve 6 is configured to switch in response to an electric signal output from the control device 10, and supplies pneumatic pressure from a pneumatic source (not shown) to the actuator 2, for example, when an on signal is applied.

The control device 10 is an electric type including a digital microcomputer, a shift register, a timer, etc., and is supplied with information regarding tightening torque from a torque sensor 7 attached to the power screw tightening device 1. Input information regarding the target tightening torque To predetermined by the formula setting device 11, the target drive stop torque Tc at the start of operation of the screw tightening device, and the number of samples n when calculating the average deviation (ΔT). Based on this information, the average deviation from the target tightening torque and the target drive stop torque are calculated according to the flowchart shown in FIG. It is now possible to control the system to stop it.

Next, with reference to the flowchart shown in FIG. 2, the implementation procedure of the drive stop control method according to the present invention will be explained.

First, in the first step 1, the tightening completion torques T ₁ , T ₂ for each screw pair and pair over a predetermined number of consecutive past n times than the previous screw pair and pair are determined, and the number of samples is n depending on Tn. The average value of the tightening end torque is calculated.

Note that when the screw tightening device starts operating, the past tightening end torques T ₁ , T ₂ ...Tn do not exist, so although these are not shown in the flowchart of Fig. 2, when the control device starts operating, All torques are automatically set to the target tightening torque T ₀ .

Next, in step 2, the target tightening torque To is subtracted from the average value to calculate the average deviation ΔT with respect to the target tightening torque To.

Next, in step 3, K (however, 0<K≦1)
The previous target drive stop torque is set as a correction factor.
A new corrected target drive stop torque Tc is calculated by subtracting ΔT·K from Tc. With this correction,
The target drive stop torque Tc is corrected to be reduced when the average deviation ΔT is a positive value, and on the contrary, corrected to be increased when the average deviation ΔT is a negative value.

Note that the correction coefficient K is a coefficient for correcting the target drive stop torque Tc based on the average deviation ΔT. This correction coefficient is a value that may be obtained experimentally, for example, and the higher the value within the above range, the higher the correction amount for the target drive stop torque.

Next, in step 4, the electromagnetic switching valve 6 is energized, air pressure is supplied to the actuator 2, and it is determined whether or not the power screw tightening device 1 has started. A start command for the screw tightening device 1 is issued based on a start signal from the setting device 11 or a start signal from another related device.

When the power screw tightening device 1 starts, the process proceeds to step 5, and in step 5, the time from the time when the screw tightening device starts, that is, the time from the time when screw tightening is started. A timer is turned on.

Next, in step 6, _t1 is a first predetermined value, _t2 is a second predetermined value larger than _t1 , and the timer value t of the timer is greater than or equal to the first predetermined value t1, and the second predetermined value is greater than _t1 . A determination is made as to whether or not the second predetermined value _t2 is less than or equal to the second predetermined value t2.
In this judgment, if t ₁ ≦t≦t ₂ is not satisfied, the process proceeds to step 7, where it is judged whether or not the timer value t of the timer is greater than or equal to the second predetermined value t ₂ .
In this determination, if t> _t2 is not satisfied, the process returns to step 6.

Furthermore, the predetermined value t ₁ determines the predetermined time after the start of tightening.
and _t2 are values that may be determined experimentally, for example, in relation to the target drive stop torque Tc.

In the determination at step 6, if t ₁ ≦t≦t ₂ , the process proceeds to step 8, where the tightening torque T detected by the torque sensor 7 is input.

Next, in step 9, it is determined whether the detected tightening torque T is substantially equal to the target drive stop torque Tc. If T≈Tc, the process returns to step 6; if T≈Tc, the process proceeds to step 10. In this case, the determination as to whether T≈Tc may be made, for example, by determining whether Tc-a≦T≦ _C +b, where a and b are positive constants determined experimentally.

Thus, in steps 6 to 9, it is determined whether the tightening torque T has substantially reached the target drive stop torque Tc within the predetermined time _t1 to _t2 after the start of tightening.

For example, when the tightening torque T changes as shown by solid lines A to C in FIG. 4, a YES determination is finally made in step 9. On the other hand, when the tightening torque T changes as shown by the broken line D in Fig. 4,
If the target drive stop torque Tc has already been exceeded at time _t1 , and the tightening torque T changes as shown by the broken line E in Figure 4, the target drive torque Tc will not be reached even at time _t2 . Therefore, in either case, a negative determination is made in step 9, and a yes determination is made in step 7 when time t exceeds _t2 .

In step 10, the energization to the electromagnetic switching valve 6 is stopped, thereby cutting off the supply of air pressure to the pneumatic rotary actuator 2, and the rotational drive of the screw fastener 5 by the actuator is stopped. Also, the timer is turned off and reset in preparation for the next cycle.

Next, in step 11, the tightening torque T at the stage when the rotation of the screw fastener 5 has completely stopped, that is, the tightening end torque T _F is inputted from the torque sensor 7.

Next, the process advances to step 12, and in this step 12, it is determined whether the tightening end torque T _F is within the range of the lower limit T _OL or more of the target tightening torque To and less than the upper limit T _OU . It will be done. When T _OL ≦T _F ≦T _OU , OK is displayed on the display 12 in step 12a (appropriate tightening is performed so that the tightening end torque is within the range of the target tightening torque lower limit value or more and upper limit value or less). If T _OL ≦T _F ≦T _OU is not satisfied, NO is displayed on the display 12 in step 12b.
An indication (indication indicating that proper tightening is not performed in which the tightening end torque falls within the range between the lower limit value and the upper limit value of the target tightening torque, and that the screw pair product is a defective product) is performed.

After steps 12a and 12b, proceed to step 13, in which the tightening end torque for calculating the average value stored in the shift register is calculated.
T ₁ , T ₂ ...T _o-1 are each shifted up one by one.

Next, in step 14, the final tightening torque
T _F is set as the tightening end torque T ₁ for calculating the next average value, and then the process returns to step 1, where the average value is updated as described above.

In addition, in step 7, if the timer value t> _t2, the screw pair is a defective product, so step 7 is performed.
Proceed to 15. In this step, the solenoid switching valve 6
By stopping the power supply to the motor, the operation of the power screw tightening device is stopped, and the timer is turned off and reset in preparation for the next cycle. The process then proceeds to step 16, in which NG is displayed on the display 12, and then the process returns to step 4. Therefore, in this case, the average value is not updated.

In addition, the tightening completion torque in step 11 above
Since the tightening torque T detected by the torque sensor 7 rapidly decreases after the rotation of the screw fastener 5 has completely stopped, T _F can be determined by a routine such as that shown in FIG. 3, for example. It's fine.

At step 11a in FIG. 3, the current tightening torque Ti is input.

In step 11b, it is determined whether or not the previous tightening torque T _i-1, which was rewritten in step 11d described later, exists. If T _i-1 does not exist, step 11d is performed. If T _i-1 exists, proceed to step 11c.

In step 11c, the current tightening torque Ti
It is determined whether the difference between the tightening torque T _{i-1 and the previous tightening torque T i-1} is 0 or negative. If the screw tightener 5 continues to tighten due to overrun, this difference will be positive, so step
A YES determination is made in step 11c, and the process proceeds to step 11d. In step 11d, the current tightening torque Ti is rewritten to T _i-1 and the process returns to step 11a.

If the threaded pair is no longer tightened due to overrun of the threaded fastener, the step
In step 11c, a YES determination is made, and in step 11e, the previous tightening torque T _i-1 is the tightening end torque.
It is said to be T _F.

Thus, according to this embodiment, for example, when the tightening torque T changes as shown by the solid line B in FIG.
As shown by Tc' in FIG. 4, the target drive stop torque Tc is corrected to be reduced, and the drive of the screw fastener 5 is stopped early, so that the tightening due to overrun of the screw fastener is reduced. Since the amount of increase in torque is reduced, the tightening torque after the drive of the screw fastener is stopped changes as shown by the dashed line in Fig. 4, and finally reaches almost the target value. It will be equal to the tightening torque To. Conversely, if the tightening torque changes as shown by solid line C in Figure 4,
As shown by Tc'', the target drive stop torque is corrected to increase, and as a result, the drive of the screw fastener is stopped at a relatively late stage, which reduces the tightening torque due to overrun of the screw fastener. Since the amount of increase is increased, the tightening torque after the drive of the screw fastener is stopped changes as shown by the dashed line in Fig. 4, and in this case as well, the final result is It becomes approximately equal to the target tightening torque To.

Although the target drive-stop torque is corrected even when the tightening torque changes as shown by the solid line A in FIG. 4, the amount of correction in this case is very small.

Further, according to the above-described embodiment, due to a defect in the screw pair to be tightened, the tightening torque T changes as indicated by the broken line D or E in FIG. Tightening torque T within ₁ ~ t ₂
When does not reach the target drive stop torque Tc,
Since the next target drive stop torque is not corrected, it is reliably avoided that the target drive stop torque is corrected based on an abnormal tightening result.

[Effects of the Invention] As is clear from the above explanation, according to the drive stop control method for a power screw tightening device according to the present invention, the average value of the tightening end torque over a predetermined number of times in the past and the target tightening The deviation from the torque is calculated, and the next target drive stop torque is corrected to be reduced or increased depending on the size and sign of the deviation, and thereby the overrun of the screw fastener is corrected depending on the size and sign of the deviation. The amount of increase in tightening torque caused by Therefore, even if the physical and mechanical properties of the screw pairs change or the operating conditions of the screw tightening device change, each screw pair can be tightened with a torque substantially equal to the target tightening torque. Can be done.

Further, according to the method of the present invention, if the tightening torque does not reach the target drive stop torque within a predetermined time after the start of tightening due to a defect in the screw pair to be tightened, the next target drive stop Since the torque is not corrected, the target drive stop torque is corrected based on the abnormal tightening results, and subsequent screw pairs may be tightened with a torque substantially equal to the target tightening torque. This will definitely prevent you from being unable to do so.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a power screw tightening device and its control device used to implement the drive stop control method according to the present invention, and FIG. 2 is a drive stop control method for a power screw tightening device according to the present invention. Flowchart showing the implementation procedure, Figure 3 is step 11 of Figure 2.
FIG. 4 is a flowchart showing an example of how to obtain the tightening end torque T _F in the process, and FIG. 4 is a graph showing the relationship between the time t after the start of tightening and the tightening torque T. 1...Power screw tightening device, 2...Pneumatic rotary actuator, 3...Reduction gear device, 4...Joint, 5
...screw fastener, 6...electromagnetic switching valve, 7...torque sensor, 10...control device, 11...setting device, 12...
display.

Claims (1)

[Claims] 1. A drive stop control method for a power-operated screw tightening device that repeatedly tightens multiple screw pairs of the same type to the next screw pair after completing the tightening of one screw pair. Measure the tightening torque, stop the drive of the screw tightening device when the tightening torque reaches the target drive stop torque within a predetermined time after the start of tightening, measure the tightening end torque after the tightening is completed,
The deviation between the average value of the tightening end torque over a predetermined number of times in the past and the predetermined target tightening torque is calculated, and the next target drive stop torque is reduced or reduced depending on the magnitude and sign of the deviation. If the tightening torque does not reach the target drive stop torque within the predetermined time after the start of tightening, the drive of the tightening device is stopped and the target drive stop torque is not corrected. A drive stop control method for a power screw tightening device.