JPH03103608A - Screw-tightening controller - Google Patents

Abstract

PURPOSE:To securely place a screw and permit it to be securely screwed in by adding motor current detected by a current detecting means to a rotation speed instructing signal with an adding means and controlling with a power supply means for applying voltage according to the addition signal to a motor. CONSTITUTION:A start signal S is input via a start signal shutting circuit 2 to a speed instructing circuit 3 together with reference speed V1 from a speed reference setting circuit 4, and the output (a) of the circuit 3 is input to an adding circuit 5 together with a current monitor signal (b) from a current detecting circuit 8 of a motor 1a. The output P of the adding circuit 5 is input to a power amplifying circuit 6 and voltage V2 according to the addition signal P is output to the motor 1a. A power amplifying circuit 6 limits current to the motor 1a to with a current limiter circuit 7, and a torque-up detecting circuit 9 compares the monitor current (b) with a signal l of a reference value setting circuit 10 and outputs a torque-up signal (m) when b>l. Therefore high voltage can be applied to the motor 1a according to an increase in motor current to permit secure screwing.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a screw tightening control device that controls an electric screwdriver during screw tightening.

(Prior Art) In order to tighten screws, an electric screwdriver consisting of a DC motor and a bit connected to the rotating shaft of the DC motor has been widely used. Conventionally, in order to control this electric screwdriver and tighten screws, the torque to rotate the bit is obtained by applying a constant voltage to a DC motor, and the current flowing through the motor is monitored to ensure that the current exceeds a predetermined value. A method has been adopted in which the power supply to the motor is cut off when the
(See Publication No. 9599).

(Problem to be solved by the invention) When screwing a screw that has already formed a female thread and a male thread into the female thread, the torque of the motor mentioned above is extremely high during the screwing process. Since the current flowing through the motor increases rapidly when the screw is seated, the control method described above is sufficient.

However, for example, when tightening screws on plastic or the like, tapping screws are mainly used while forming female threads in prepared holes, so the torque during tightening may become quite high due to variations in the prepared holes and tapping screws. In this case, the control method for obtaining rotational force by applying a constant voltage to the motor of the electric screwdriver has a problem in that the bit may stop with the head of the screw floating in the middle of screwing.

Figure 3 (A). (B) is a diagram showing the voltage applied to the motor of the electric screwdriver and the current flowing through the motor, respectively, to further explain this problem.

Conventionally, a constant voltage is applied to the motor for a predetermined period from time to to time t1.
3, the rotational speed n' of the bit decreases as the screwing torque increases. Here, the margin Δ' for normal screw-in is very small, so if the screw-in torque increases abnormally, the rotational speed will drop sharply as shown by the broken line in Figure 3 (B), and in this case, the screw The bit will stop rotating before it is seated.

In order to solve the above problem, it may be possible to set the above constant voltage to a high value. In this case, the rate of occurrence of the problem of the bit stopping in the middle of screwing in will be reduced, but this time, the tapping screw head If high torque is required to tighten the screw further when the screw is floating, the head of the tapping screw may be crushed and the bit may spin idly, and the pilot hole may be slightly smaller than the diameter of the tapping screw. When the threads vary in a wide direction, a problem arises in that the female threads become crushed.

In view of the above-mentioned problems, the present invention provides a screw tightening control that can securely seat the screw without stopping the bit due to the load during screw tightening as the screw tightening progresses and the torque increases. The purpose is to provide a device.

(Means for Solving the Problems) A screw tightening control device of the present invention includes a screw tightening bit and a motor for rotating the bit, which has a variable speed characteristic in which the rotation speed decreases as the load torque increases. In a screw tightening control device for controlling an electric screwdriver, the screw tightening control device includes: a current detection means for detecting a current flowing through the motor to obtain a current monitor signal; The present invention is characterized in that it includes an adding means for outputting an added signal by adding , and a power supply means for inputting the added signal and applying a voltage to the motor according to the added signal.

(Function) In the present invention, the current monitor signal is obtained by the current detection means, the speed command signal and the current monitor signal are added by the addition means to obtain the addition signal, and the addition signal is obtained by the power supply means. Since a voltage according to the signal is applied to the motor, as the screw tightening progresses and the load torque increases, a voltage corresponding to the magnitude of the load torque is applied to the motor, thereby preventing the screw from floating. is definitely prevented.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the screw tightening control device of the present invention.

When a start signal S is input manually from an instruction device (not shown) that instructs the start of rotation of the motor la of the electric screwdriver l or a button switch when giving this instruction manually, this start signal S starts the rotation of the motor la. The signal is input to the speed command circuit 3 via the start signal cutoff circuit 2 for cutting off the start signal S when stopping the start signal S. The reference speed vl of the motor la set by the speed reference setting circuit 4 is also input manually to this speed command circuit 3.
A speed command signal a is output to the adder circuit 5 at the timing when the start signal S is manually input. This addition circuit 5
is an embodiment of the adding means of the present invention. The above adding circuit 5
Now, this speed command signal a and the current monitor signal b described later
are added to generate an addition signal p, which is output to the power amplifier circuit 6. This power amplification circuit 6 is one aspect of the power supply means of the present invention, and this power amplification circuit 6 supplies a voltage v2 corresponding to the addition signal p to the motor la of the electric driver 1.
Apply. However, a current limiter circuit 7 is connected to the power amplifier circuit 6, and the current is limited so that the current flowing into the motor 1a is below a predetermined value.

The electric screwdriver 1 has the motor la as shown in the figure.
, a bit lb, and a coupling lc that connects the motor la and the bit lb. Here, the number of rotations of the bit lb is assumed to be n. The current flowing through the motor la is monitored by a current detection circuit 8, which is one aspect of the current detection means of the present invention, and the current monitor signal b is obtained. As described above, this current monitor signal b is input to the adder circuit 5 and added to the speed command signal a. This current monitor signal b is also input to the current limiter circuit 7, and as described above, current is limited so that a current exceeding a predetermined value does not flow to the motor 1a. The current monitor signal b is also input to the torque-up detection circuit 9. This torque up detection circuit 9 receives the input current monitor signal b and the reference value setting circuit lO.
When the current monitor signal b exceeds the reference value D, it is assumed that the screw is seated and a torque up signal m is output.

This torque up signal m is supplied to the start signal cutoff circuit 2.
is input. As shown in the figure, this start signal cutoff circuit 2 is composed of a two-man power AND circuit 2a, a timer 2b, and an NPN transistor 2c which operates as a switch. When the start signal S is output from the start signal cutoff circuit 2 and the torque up signal m is input, the timer 2b starts operating and cuts off the start signal S after a predetermined period of time has elapsed. Due to this interruption, no voltage is applied to the motor la, and the rotational torque of the bit lb disappears.

FIG. 2 shows temporal changes in the speed command signal a, the voltage V2 applied to the motor la, the current monitor signal b, and the rotational speed n of the bit in the block diagram shown in FIG. It is a diagram. The operation of the screw tightening control circuit shown in FIG. 1 will be further described with reference to FIG. 2.

FIG. 2(A) is a diagram showing the change over time of the speed command signal a outputted from the speed command circuit 3. The start signal S rises at time to, which is the moment when it is input, and time t, which is the moment when the start signal S is cut off by the start signal cutoff circuit 2! It's falling.

FIG. 2(B) and FIG. 2(C) show the voltage vz1 output from the power amplifier circuit 6 and applied to the motor la, and the current flowing through the motor la (detected by the current detection circuit 8). FIG. 3 is a diagram showing a change in current monitor signal b) over time. At the moment when the voltage is applied to the motor 1a, an inrush current flows and reaches a peak 1l, and from time t2 when screwing is started, as the screwing torque increases, the current flowing through the motor ib increases, and the moment the motor ib is seated. After time t3, the current limiter circuit 7 operates to clip the current to the predetermined value.

Further, since the voltage v2 corresponds to the sum signal p obtained by adding the speed command signal a and the current monitor signal b by the adding circuit 5, it increases as the current monitor signal b increases. .

FIG. 2(D) is a diagram showing the change over time in the rotational speed n of the bit lb. Although there is some speed fluctuation while screwing is being performed (between time t2 and time t3), the speed is kept much more constant than in the conventional control method described above. In this way, even if the load torque associated with screwing increases, by maintaining a substantially constant speed, the margin Δ is changed from the margin Δ′ (third
(see figure), and screws in securely.

(Effects of the Invention) As described above in detail, the screw tightening control device of the present invention is configured to apply a higher voltage to the motor as the current flowing through the motor increases, so that the torque during screw tightening is reduced. Even if the rise is large, screwing can be performed reliably.

[Brief explanation of drawings]

1 is a block diagram showing one embodiment of the screw tightening control device of the present invention; FIG. 2 is a diagram showing temporal changes in signals etc. of each part of the block diagram shown in FIG. 1; The figure is a diagram showing the voltage applied to the motor of an electric screwdriver and the current flowing through the motor, for explaining the conventional problems. 1... Electric screwdriver 1a... Motor 1b
...Bit 1c...Coupling 2...Start signal cutoff circuit 3...Speed command circuit 4...Speed standard setting circuit 5...Addition circuit 6.
...Power amplifier circuit 7...Current limiter circuit 8...Current detection circuit 9...Trick-up detection circuit 10...Reference value setting circuit B. Ω

Claims (1)

[Claims] In a screw tightening control device that controls an electric screwdriver that includes a screw tightening bit and a motor for rotating the bit, the motor has a variable speed characteristic in which the rotation speed decreases as the load torque increases. current detection means for detecting a current to obtain a current monitor signal; addition means for outputting an addition signal by adding the current monitor signal to a speed command signal instructing the rotational speed of the motor; and inputting the addition signal. and power supply means for applying a voltage to the motor according to the addition signal.