JP2725322B2 - Screw tightening method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw tightening method for precisely realizing a wide range of tightening of various screws such as small screws, wood screws, tapping screws and the like.

2. Description of the Related Art In recent years, with the diversification of screws such as minute screws and the emergence of various works, high-quality screw tightening work having a high tightening accuracy, a wide tightening torque range, and the like has been required.

Hereinafter, a screw fastening operation by a conventional screw fastening device will be described with reference to the drawings. FIG. 5 shows an outline of the screw tightening device, and FIGS. 6 and 7 show examples of an electrically controlled electric screwdriver. In FIG. 6, reference numeral 1 denotes a rectifier. Reference numeral 2 denotes a power transistor (hereinafter referred to as power Tr) for controlling the power of the motor. Reference numeral 3 denotes a driver motor, 4 denotes a detection resistor for detecting a current flowing through the motor, 5 denotes a current determination level adjustment volume, 6 denotes a comparator and a comparator thereof, and 7 denotes a transistor for driving a power Tr. Seventh
In the drawing, reference numeral 8 denotes an example of a current flowing through the motor, reference numeral 9 denotes a determination level, and reference numeral 10 denotes a level at which screw tightening is completed.

The operation of the screw tightening device configured as described above will be described below. First, power is supplied to the motor 3 by a start signal given to the power Tr2, the motor 3 starts rotating, and the air cylinder 11 operates to lower the electric driver 12. The vacuum suction pipe 13 hits the catcher 14, the screw 15 is sucked up and the bit 16
Located at the tip. Further, the electric screwdriver 12 continues to descend and sits on the work, the current rises, and the level adjustment volume 5
When the value coincides with the value 9 set in the above, the comparator 6 operates, the power transistor Tr2 is turned off by the drive transistor 7, and the screw tightening is completed.

8 and 9 show another example of a conventional mechanically controlled electric screwdriver, in which 3 is a motor, 17 is a driving cam, 18 is a driven cam, and 16 is a conventional cam. A tightening bit, 19 is a torque spring, 20 is a limit switch, and 15 is a screw.

The operation of the mechanical electric screwdriver configured as described above will be described below. The motor 9 shown in FIG.
Electric power is supplied in the form of the circuit shown in the figure, the motor 3 rotates, and in the same manner as in the conventional example, the screw 15 is held at the tip of the rotating bit 16 by vacuum suction during the downward movement.
Screw tightening is performed. Then, when the screw 15 is seated on the work and reaches the torque value set by the torque spring 19, the driving cam 17 and the driven cam 18 are put on the heads of the respective cams as shown in FIG. Then, the limit switch 20 operates and the power to the motor 3 is turned off, and screw tightening is completed.

However, in the above two conventional configurations, it is very difficult to determine the level in a short time when the motor is rotating at a high speed and to stop the motor without inertia even when using an electric method. However, it was difficult to set a wide range of tightening torque values even with a mechanical method, and it was mechanically problematic in terms of noise and life.

The present invention has been made in view of the above problems, and provides a screw tightening control device for an electric screwdriver that controls a motor that rotates at a high speed and performs screw tightening with a constant tightening force and high accuracy.

Means for Solving the Problems And a technical means of the present invention for solving the above problems includes a first step of detecting rotation of a drive unit for driving a screw-fastening screwdriver and current flowing in the drive unit. ,
The seating on the work is detected by the detected detection signal,
A second step of applying a reverse rotation brake to the drive unit, a third step of driving the drive unit with a torque according to the work and the screw for a predetermined time after applying a predetermined current limit, and And gradually increasing the preset angle from the seated state.

That is, a screw seat detection circuit for a motor for an electric screwdriver rotating at a high speed, a reverse rotation brake circuit for rolling down the inertia of the motor and the mechanism, and a rotation position detection means for tightening the screw with a constant and high accuracy are provided. The power supply and the drive circuit of the motor are provided with a PWM control circuit so that the screw can be tightened with a wide range of tightening torque.

Operation The operation of this technical means is as follows. The higher the speed of the motor, the greater the change from rotation to stop, so detection of seating can be carried out in a very short time, and over-tightening due to inertia and instability due to the reverse rotation brake circuit including current limiting also occur After that, by controlling the power supply and the power Tr, the tip of the bit is once pressed in the rotating direction instead of the screw head to detect the exact seating position, and by tightening the preset angle from there, Even when the screw tightening is completed, inertia does not occur, and accurate screw tightening with a fixed tightening force can be realized.

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a perspective view of a screw tightening robot according to a first embodiment of the present invention. In FIG. 1, 11 is an air cylinder, 21 is a reduction gear unit, 22 is an assembly robot, 23 is a screw supply unit, and 35 is a rotation detector.
FIG. 2 is a rotation block diagram of the screw tightening control device in the first embodiment. In FIG. 2, reference numeral 24 denotes a control CP.
U and 25 are R with control software and screw tightening pattern
OM and 26 are RAMs for storing screw tightening conditions. 27 is a chopper type power supply unit, 28 is an analog / digital converter (hereinafter A / D converter)
29, a current detection conversion circuit; and 30, a speed detection seating detection circuit. Reference numeral 31 denotes a motor driver which includes a power Tr 32, a control circuit 33 for the power Tr, a current detector 34, and the like. Reference numeral 3 denotes an electric driver motor, and reference numeral 35 denotes a rotation detector. 36 is a display for screw tightening torque value and tightening condition, etc.
37 is a switch for data input and operation, and 38 is a connection interface circuit (hereinafter referred to as I / F) for connection to external equipment, which receives start / screw tightening conditions 39, etc., and outputs signals 40 for completion, failure, torque data, etc. I do. 41 is a command signal to the chopper type power supply, 42 is an output voltage to the electric driver motor 3,
Reference numeral 43 denotes a control signal and a brake signal of the power Tr for driving the electric driver motor 3.

The operation of the screw tightening control device configured as described above will be described with reference to FIGS. 1, 2, 3 and 4. FIG. 3 shows a current curve flowing through the electric tribar motor 3, the value of which is indicated by the current detector 34,
The current fluctuation is read by the current detection conversion circuit 29 and the A / D converter 28, and the speed fluctuation by the rotation detector 35 in FIG. 2 is also read through the speed detection conversion circuit 30 and the A / D converter 28. The unit 27 and the power Tr 32 are PWM controlled. At the same time, the rotation angle of the bit 16 can be calculated by the counter of the CPU 24 from the resolution of the rotation detector 35 and the reduction ratio of the reduction gear unit 21, and the rotation angle can be detected.

When the motor 3 was started, the starting current 44 shown in FIG. 3 flowed. After the screw 15 has been screwed into the work 45, FIG.
When the screw 15 is seated on the work A by the tightening bit 16 as shown in FIG. 4, the positional relationship between the bit 16 and the screw 15 is shown in FIG.
The current changes as shown at the inflection point 46 in FIG. The change in the rotation by the rotation detector 35 and the speed detection / seating detection circuit 30 in FIG. 2 and the change in the current by the current detector 34 and the current detection conversion circuit 29 are read from the CPU 24 to control the reverse rotation brake command from the CPU 24. When the current is output to the motor 33 at time t ₁ and the current of the motor 3 is limited, the brake current 47 shown in FIG.
4 (c). Next, after the set time, a low primary tightening current value 48 according to the work and the screw type is added, and as shown in FIG.
Outputs for t ₂ hours so that no impact is applied when hitting 15 again.
Next, while the pulses output from the rotation detector are counted by the CPU 24, the current value of the electric driver motor 3 is gradually increased as shown by a curve 49, and the current value 50 at which the pulse number corresponding to the preset angle has been output has been completed. in driving the t ₃ hours electric screwdriver motor 3 is stopped so that there is no inertia of the motor and the gear. Thus, screw tightening is completed.

In the present embodiment, a brushless DC motor is assumed as the electric driver motor 3 and a Hall sensor is assumed for rotation detection. However, as another embodiment, a rotation detector 35 is used.
(Not shown) using an encoder.

Effect of the Invention As described above, the present invention provides a first step of detecting the rotation of a drive unit that drives a screw-fastening screwdriver and a current flowing through the drive unit, and applying a detection signal to the workpiece based on the detected signal. A second step of detecting a seat and applying a reverse brake to the drive section, and a third step of driving the drive section with a torque corresponding to the work and the screw for a predetermined time after applying a predetermined current limit. A fourth step of gradually increasing the current of the drive section and tightening a preset angle from the seated state;
By making the process shown in the figure, tighten the screw with an appropriate torque from an accurate seated state, and finally tighten a certain angle to achieve uniform screw tightening and achieve a significant improvement in tightening force, A screw tightening electric screwdriver having a wide range of tightening torque control can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view of a robot incorporating a screw tightening device according to a first embodiment of the present invention, FIG. 2 is a tightening control circuit diagram of the screw tightening device according to the first embodiment, and FIG. FIG. 4 (a) is a cross-sectional view of a vacuum suction pipe showing a state in which a screw is seated on a work, and FIGS. 4 (b), (c) and (d) are screws. FIG. 5 is a side sectional view of a conventional screw tightening device, FIG. 6 is a conventional electric circuit diagram, FIG. 7 is the same current curve diagram, and FIG. 8 is a conventional mechanical device. FIG. 9 is a sectional view of a bit showing the configuration, and FIG. 9 is the same electric circuit diagram. 3 ... Electric screwdriver motor, 11 ... Air cylinder, 12 ... Electric screwdriver, 13 ... Vacuum suction pipe, 15
... Screw, 16 ... Bit, 21 ... Reduction gear unit, 22
…… Assembly robot, 23 …… Screw supply unit, 35 ……
Rotation detector.

Claims (1)

(57) [Claims] A first step of detecting a rotation of a driving section for driving a screw-fastening screwdriver and a current flowing in the driving section; and detecting a seating on a workpiece by the detected detection signal. The second to apply the reverse brake to the drive unit
And a third step of driving the drive unit with a torque corresponding to the work and the screw for a predetermined time after applying a predetermined current limit, and gradually increasing the current of the drive unit, and starting from a seated state in advance. A screw tightening method including a fourth step of tightening a set angle.