JPH0624715B2 - Screw tightening control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Industrial field of application >> The present invention relates to the torque rate at the initial tightening of each screw when a screw fastener such as a nut runner is used near the limit of its maximum torque generation capability. The present invention relates to a screw tightening control device that automatically selects and drives either a torque method or an angle method.

<< Prior Art >> Conventionally, as a control method of a screw fastening machine, a torque method in which a torque at the time of tightening is detected and controlled by this is used, and an angle method in which a tightening angle is controlled.

However, since each screw has variations in the friction coefficient of the bearing surface and the threaded portion, in the torque method that tightens with the same torque regardless of this friction coefficient, the variation in the friction coefficient causes variations in the bolt axial force. On the other hand, in the angle method of tightening a predetermined angle regardless of the friction coefficient, there is almost no variation in the bolt axial force, but the variation in the friction coefficient is opposite to the variation in the tightening torque. There is a problem saying that it will appear.

As described above, since both tightening methods have advantages and disadvantages, it is necessary to use each tightening method properly according to the type of the object to be fastened or the required tightening accuracy.

Therefore, as disclosed in Japanese Patent Laid-Open No. 58-56775, a selection switch for selecting either the torque method or the angle method is provided, and the torque method or the angle method is selected according to the tightening condition. A screw tightening device has been proposed, which can be freely selected and an optimum tightening method can be adopted.

<< Problems to be Solved by the Invention >> However, in this known screw tightening device, which tightening method is selected is artificially performed. Therefore, if it is not always clear which one of the tightening method, the torque method or the angle method, is suitable depending on the type of the fastened body, or the friction coefficient is greatly different between fastened bodies, the unsuitable fastening method is inappropriate. There is a problem such that the desired fastening force cannot be obtained by selecting the additional method.

Also, especially in the assembly production line, etc., from the viewpoint of its installation space, etc., the smallest screw fastening machine is adopted, and this screw fastening machine is driven near the limit of its maximum generated torque capacity. ing.

When the screw fastener is driven near the limit of its capacity in this way, the torque method has conventionally been used for tightening the screw, but this torque method allows the optimum shaft to be used when the friction coefficient is small. There has been a problem that excessive screws are unnecessarily tightened beyond the rotation angle at which force is generated.

Therefore, in such a case, it is conceivable to control the screw fastener by the angle method. However, in this angle method, if the screw has a large friction coefficient, the screw fastener will generate the maximum torque before rotating it by a predetermined angle. There is a case where the limit is reached and it is impossible to rotate to a predetermined angle, and in such a situation, the rotation angle is controlled by the angle method control even if the axial force is within the allowable range. There is a problem that if the angle is not satisfied, this is determined to be defective.

The present invention has been made in view of the above circumstances, and an object thereof is to calculate the torque rate in the initial tightening stage after the screw is seated by the screw fastening machine to grasp the magnitude of the friction coefficient of each screw. However, when the friction coefficient is small, the angle method is automatically selected to prevent unnecessary tightening, while when the friction coefficient is large, the torque method is automatically controlled to prevent undue defect determination. It is to provide a screw tightening control device capable of

<< Means for Solving Problems >> In order to achieve the above-mentioned object, the screw tightening control device of the present invention has the first torque T ₁ and the second torque T ₁ at the initial tightening stage after the screw is seated by the screw fastener. calculating means for calculating an initial torque rate from an angular screw tightening between the torque T _2,
A first comparator for comparing whether or not the initial torque rate is within a preset reference torque rate range;
When the comparator determines that the initial torque rate is within the range of the reference torque rate, the initial torque rate is calculated from the maximum value of the torque generated by the screw fastening machine and the optimum axial force angle and is calculated in advance. A second comparator for comparing whether or not a boundary torque rate set as a boundary between the torque method and the angle method is exceeded, and the initial torque rate in the second comparator is equal to or less than the boundary torque rate. An angle method logic circuit that drives the screw fastening machine by the angle method when it is determined that
And a torque method logic circuit for driving the screw fastener by a torque method when the second torque comparator determines that the initial torque rate is equal to or higher than the boundary torque rate.

<< Operation >> The initial torque rate is calculated from the screw tightening angle between the first torque T ₁ and the second torque T ₂ set at the initial tightening stage of the screw fastening machine, and this is the preset reference torque rate. If the initial torque rate is outside the range of the reference torque rate as a result of this comparison, it is treated as a torque rate initial trouble.

On the other hand, as a result of this comparison, when the initial torque rate is within the range of the reference torque rate, the initial torque rate is again compared with the preset boundary torque rate between the torque method and the angle method, and it is not exceeded or exceeded. Or compare.
Then, as a result of this comparison, when it is determined that the initial torque rate is equal to or lower than the boundary torque rate, the screw fastening machine is driven by the angle method, and when it is determined that the initial torque rate is equal to or higher than the boundary torque rate, the screw fastening machine is driven by the torque method. Drive it.

<< Embodiment >> A preferred embodiment in which the present invention is applied to control of a DC nut runner will be described below. FIG. 1 shows a tightening diagram and shows a conversion range between a torque method and an angle method. The horizontal axis represents the rotation angle, and θ ₁ represents the angle at which the optimum axial force can be obtained. The vertical axis represents the torque, T ₁ is the first set torque value in the initial tightening stage after the screw is seated, T ₂ is the second set torque value, and T ₃ is the full-scale torque of the DC nut runner. .

d ₁ (dT / dθ) is a value calculated back from the full-scale torque (T ₃ ) of the DC nut runner and the optimum axial force angle θ ₁ and indicates the boundary torque rate between the torque method and the angle method. The torque rate between the torque rates D ₁ and D ₂ obtained experimentally by sandwiching the boundary torque rate d ₁ was set as a normal reference torque rate range (D ₁ <dT / dθ <D ₂ ). If the torque rate is lower than D ₁ , or D
_When it was higher than ₂ , it was regarded as an abnormal torque rate.
The torque rate is within the range of the reference torque rate and tightening lower than the boundary torque rate d ₁ (D ₁ <dT / dθ
For <d ₁ ) the angle method is adopted, while the torque rate is within the range of the reference torque rate and the boundary torque rate d
_For tightening higher than ₁ (d ₁ <dT / dθ <D ₂ ), the torque was used in consideration of the capacity of the nut runner to make the axial force relatively stable.

FIG. 2 shows a theoretical circuit for driving the above DC nut runner. In this circuit, 1 indicates a DC nut runner, and this nut runner 1 is a torque transducer 1a for converting a tightening torque into a voltage and a tightening angle. It is connected to an encoder 1b that generates pulses, and is further connected to a drive motor 1c via these.

The output of the transducer 1a, together with the torque _{T 1,} T 2, _{T 3} setter 2,3,4 delivering an output signal corresponding to the set torque value, three differential amplifiers 6, 7, 8
Has been entered in. The torque T ₁ and T ₂ setters ₂ and 3 determine the torque value when calculating the torque rate, and the analog switches 10 and 11 connected in series via the differential amplifiers 6 and 7 are It is input to a logic circuit 14 that controls a torque rate (dT / dθ) calculation circuit described later.

On the other hand, the torque setting device 4 is for setting the final tightening torque value by the torque method, and is inputted to the torque method logic circuit 15 via the differential amplifier 8 and the analog switch 12 which are connected in series with the torque setting device 4. There is.

Two counters 9 and 17 that count angle pulses are connected in parallel to the encoder 1b, and the output of one counter 9 is compared with the output of the angle setter 5 that sets the final tightening angle value by the angle method. The comparator 13 is connected to the angle method logic circuit 16.

The output of the other counter 17 is the logic circuit 14
It is connected to a torque rate calculation circuit 19 through an AND gate 18 that opens the circuit only when the output signal from is output.

The torque rate calculation circuit 19 is connected to a first comparator 20, and a reference torque rate range setting device 21 for specifying a normal range of the torque rate is connected to the comparator 20 to calculate the torque rate. When the comparator 20 determines that the output signal from the circuit 19 is out of the range, the comparator 20 outputs the output signal to the logic circuit 14.

Further, the first comparator 20 is connected in series with the second comparator 22, and the second comparator 22 is connected with the torque rate setting device 23 for setting the torque rate limit of the torque method or the angle method. When the first comparator 20 determines that the output is within the range, the analog switch 21 operated by the signal from the logic circuit 14 causes the output from the first comparator 20 and the torque rate setting device. The outputs from 23 are compared.

The output side of the second comparator 22 is connected to the torque method and angle method logic circuits 15 and 16 via the logic circuit 14, and the outputs of these logic circuits 15 and 16 are input to the servo controller 24 in a parallel state. The output side of the servo controller 24 is connected to the motor 1c.

The control of the DC nut runner by the above circuit will be described below.

<Step 1> The output of the torque transducer 1a,
The output of the torque T ₁ setting device 2 is compared by the comparator 6, and when they match, the analog switch 10 is turned on,
By turning on the gate 18 via the logic circuit 14, the signal from the encoder 1b is started to be counted.

<Step 2> The output of the torque transducer 1a and the output of the torque T ₂ setting device 3 are compared by the comparator 7, and when they match, the analog switch 11 is turned on and the gate 18 is turned off via the logic circuit 14 to make the encoder. The counting of the signal from 1b is ended.

<Step 3> The torque rate dT / d is calculated from the number of angle pulses while the torque T _{1 to} T ₂ and the gate 18 are ON.
Calculate θ.

<Step 4> The torque rate obtained in Step 3 is compared with the reference torque rate range set in advance by the torque rate setting unit 21 by the first comparator 20, and the initial torque rate NG is extracted. The signal from the comparator 20 activates the logic circuit 14.

<Step 5> If the incremented torque rate is OK as determined by the first comparator 20, the logic circuit 14
Turns on the analog switch 21 and sets the torque rate set by the torque rate setting unit 23 to the second comparator 22.
In order to select the tightening method according to the torque rate, the logic circuit 14 is operated by the signal from the second comparator 22.

<Step 6> When the angle method is selected in the logic circuit 14, the angle method logic circuit 16 operates to set the tightening set angle θ.
Activates the servo controller 24 via the logic circuit 16 by comparing the output of the _first setting device 5 and the output of the encoder 1b by the comparator 13, the drive motor 1c is stopped, torque method with the logic circuit 14 is selected Then, the torque method logic 15 is activated, and the comparator 8 compares the output of the setting device 4 of the tightening set torque T ₃ with the output of the torque transducer 1a to turn on the analog switch 12 and through the tosic circuit 15. Then, the servo controller 24 is operated to stop the drive motor 1c.

FIG. 3 is a flow chart showing the operation of this embodiment, which will be described below.

When the torque T ₁ is detected in the initial stage after the screw is seated after the DC nut runner 1 is started, the angle pulse gate is turned on.
Then, pulse counting is started (step 1), when the torque T ₂ is detected, the angle pulse gate is turned off (step 2), and the torque rate (dT / dθ) is calculated from the pulse count number and torque change amount during this period. (Step 3). Torque rate dT /
The range of the reference torque rate in which dθ is experimentally obtained (D ₁ ~
It is judged whether or not it is within D ₂ ) and if it is out of this range, it is regarded as an initial trouble NG of abnormal torque rate (step 4). On the other hand, if the torque rate is within the range of the reference torque rate, it is further determined whether or not it is within the range of D _{1 to} d ₁ (step 5). Tightening is performed (step 6), and when it is not within this range, torque method is performed (step 7).

The subsequent steps are the conventional tightening of the angle method and the torque method respectively.In the case of the angle method, the set angle tightening is used to stop, but in order to prevent full-scale torque over due to changes in the torque rate during tightening. Is provided with a torque limiter (omitted in FIG. 2).

On the other hand, in the case of the torque method, it is tightened up to the set torque and stopped, but an angle limiter is provided in case of plastic elongation of the bolt (omitted in FIG. 2).

<< Effects of the Invention >> As described above, in the screw tightening control device according to the present invention,
The torque rate at the initial stage of tightening after the screw is seated by the screw fastener is calculated, and this initial torque rate is calculated from the maximum value of the torque generated by the screw fastener and the optimum axial force angle. When the initial torque rate is judged to be below the boundary torque rate, the screw fastener is driven by the angle method, while the initial torque rate is judged to be above the boundary torque rate. The screw fastener is driven by the torque method.

Therefore, it is possible to automatically select the appropriate tightening method for each screw being tightened, prevent unnecessary tightening when the friction coefficient is small, and prevent undue defects when the friction coefficient is large. A desired fastening force can be easily and surely obtained and the working efficiency can be improved as compared with the case of manually selecting the changeover switch as described above.

[Brief description of drawings]

FIG. 1 is a tightening diagram showing the conversion range of the torque method and the angle method of the present invention, FIG. 2 is a logic circuit showing the control when the present invention is applied to a DC nut runner, and FIG. 3 is FIG. 3 is a flowchart showing the operation of the embodiment of FIG. 1 ... DC nutrunner 1a ... Transducer 1b ... Encoder, 1c ... Drive motor 15 ... Torque method logic circuit 16 ... Angle method logic circuit 19 ... Computing means, 20 ... First comparator 22 ... … Second comparator

Claims (1)

[Claims] 1. A calculation means for calculating an initial torque rate from a screw tightening angle between a _first torque T ₁ and a second torque T ₂ in an initial tightening stage after a screw is seated by a screw fastener. A first comparator for comparing whether or not the initial torque rate is within a preset reference torque rate range;
When it is determined by the first comparator that the initial torque rate is within the range of the reference torque rate, the initial torque rate is calculated from the maximum value of the torque generated by the screw fastener and the optimum axial force angle. And a second comparator for comparing whether or not a boundary torque rate set in advance as a boundary between the torque method and the angle method is exceeded, and the second comparator compares the initial torque rate with the boundary. An angle method logic circuit that drives the screw fastening machine by an angle method when it is determined to be equal to or lower than the torque rate, and the screw fastening when the initial torque rate is determined to be equal to or higher than the boundary torque rate by the second comparator. A screw tightening control device comprising a torque method logic circuit for driving a machine by a torque method.