JPH03103609A - Screw-tightening controller - Google Patents

Abstract

PURPOSE:To securely screw up by providing an upper limit instructing means of motor current, a motor current detecting means, a power supply means for outputting voltage according to a speed instructing signal to prevent the motor current from exceeding the upper limit and a means for changing the upper limit after a cycle of torsion spring vibration has been completed. CONSTITUTION:A reference signal (a) of a speed reference circuit 1 and a signal (d) from an upper limit changing circuit 15 are input to an adding circuit 3, its output (e) is input to a speed instructing circuit 4, the speed instructing signal (b) is outputted to a power amplifying circuit 5 and voltage V to a motor 2a is outputted. In addition, the upper limit changing circuit 15 inputs monitor current (c) of the motor 2a of a power detecting circuit 7 and outputs a signal (m) when the current (c) exceeds the output (l) of a reference value setting circuit 9. Then a timer 11 set to a time corresponding to approximately one cycle of vibration of a torsion spring 2c is operated and a signal (o) to be input to a current limiter 6 together with a signal (d) and the monitor current is outputted. Therefore even if a load increases during screw tightening, secure screwing is possible.

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, and in particular, a motor and a bit are connected via a torsion spring. This invention relates to the control of an electric screwdriver with a structure similar to the above.

(Prior Art) In order to tighten screws, an electric screwdriver equipped with a DC motor and a bit connected to the rotating shaft of the DC motor has been widely used. In order to reduce the shock, electric screwdrivers in which the rotating shaft of the motor and the bit are connected via a torsion spring are also frequently used.

Conventionally, as a control method for the electric screwdriver when tightening a screw, 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 is at a predetermined value. A method has been adopted in which the application of voltage to the motor is cut off when the voltage exceeds the voltage (for example, see Japanese Patent Laid-Open No. 53-39599).

(Problem to be solved by the invention) When screwing a screw into a female thread that has already been formed, the torque of the motor is very small during screwing, and it is difficult to seat the screw. At times, the current flowing through the motor increases rapidly, so the control method described above is sufficient.

However, for example, when tightening screws on plastic or the like, a tapping screw is mainly used to form a female thread in a pilot hole, and therefore the torque during tightening may become quite high due to variations in the screws in the pilot hole and tapping. 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 stops with the head of the screw floating during screw-in.

In order to solve the above problem, it is possible to set the above constant voltage to a high value, and in this case, the rate of occurrence of the problem of the bit stopping in the middle of screwing will be reduced, but this time, the diameter of the tapping screw When the prepared hole is slightly wider than the conventional one, a problem arises in that the female thread is crushed.

In view of the above-mentioned problems, the present invention is capable of reliably seating the screw by restarting screwing even if the bit temporarily stops due to the load as screw tightening progresses and the load increases. The object of the present invention is to provide a screw tightening control device.

(Means for Solving the Problems) A screw tightening control device of the present invention includes a screw tightening bit, a motor having variable speed characteristics in which the number of revolutions decreases as the load torque increases, a rotating shaft of the motor, and the bit. and a coupling that transmits the rotational force of the motor to the bit via a torsion spring. an upper limit value indicating means for instructing; a current detecting means for detecting the current flowing through the motor to obtain a current monitor signal; a power supply means for applying a voltage to the motor according to a speed command signal instructing the motor; The present invention is characterized by comprising upper limit value changing means for changing the upper limit value to a higher value than the previous value.

(Function) In the present invention, even if the current flowing through the motor of the electric screwdriver reaches the upper limit value, the upper limit value is changed from the previous value when approximately one cycle of vibration of the torsion spring has passed. Since the value is changed to a high value, even if the bit is temporarily stopped due to the load, the torque of the motor is actively added to the elastic force of the torsion spring to perform additional tightening, thereby reliably preventing the screw from floating. be done.

(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.

A reference signal a instructing the start and stop of rotation of the motor 2a of the electric screwdriver 2 and a reference rotational speed is outputted from the speed reference circuit 1 and inputted to the addition circuit 3. The adding circuit 3 adds a torque increase signal d, which will be described later, to the reference signal a to obtain an added signal e, and inputs this added signal e to the speed command circuit 4. The speed command circuit 4 generates a speed command signal b indicative of the actual rotational speed of the motor 2a in response to the addition signal e. This speed command signal b is input to a power amplification circuit 5, which is one aspect of the power supply means of the present invention, and the power amplification circuit 5 applies a voltage V according to the speed command signal b to the motor 2a.

However, a current limiter circuit 6, which is one aspect of the upper limit value indicating means of the present invention, is connected to the power amplifier circuit 5.
Current limitation is performed so that the current flowing through the motor la is below a predetermined upper limit value.

As shown in the figure, the electric screwdriver 2 has the motor 2
a, a bit 2b for screwing in by rotating the screw, and a coupling 2d for connecting the motor 2a and the bit 2b via a torsion spring 2c. Here, the torsion angle of the bit 2b with respect to the rotating shaft of the motor 2a is represented by ψ.

The current flowing through the motor 2a is monitored by a current detection circuit 7, which is one aspect of the current detection means of the present invention, and a current monitor signal C is obtained. This current monitor signal C is input to the current limiter circuit 6, and as described above, current is limited so that a current exceeding the upper limit value does not flow to the motor la. The current monitor signal C is also input to the torque-up detection circuit 8. The torque up detection circuit 8 compares the input current monitor signal C with the reference value 1 input from the reference value setting circuit 9, and when the current monitor signal C exceeds the reference value 1, the screw is turned off. Once it is assumed that the driver is seated, a torque up signal m is output. The torque up signal m is set to the above-mentioned standard so that it is output when the current limiter circuit 6 is activated, that is, when the current flowing through the motor 2a exceeds the above-mentioned upper limit value, or when it exceeds the above-mentioned upper limit value. The value setting circuit 9 has been adjusted.

The flip-flop IO is set by the torque-up signal m, and the timer 11 is activated at the set timing, and after a time corresponding to approximately one cycle of the vibration of the torsion spring 2c has elapsed, the signal is sent to the addition amount setting circuit 12. to output the torque increase signal d. The torque increase signal d is input to the adder circuit l3.

The adder circuit 13 adds the torque increase signal d to the limiter reference signal n indicating the upper limit value outputted from the limiter reference circuit 14, and outputs an upper limit value signal 0. This upper limit signal 0 is manually input to the current limiter circuit 6, where the current monitor signal C is compared with the upper limit signal 0, and the electric power is controlled so that the current flowing through the motor 2a does not exceed the upper limit value. Controls the amplifier circuit 5. In this embodiment, each circuit from the torque up detection circuit 8 to the limiter reference circuit 14 constitutes an upper limit value changing circuit 15 as one aspect of upper limit value changing means.

FIG. 2 is a diagram showing temporal changes in signals, etc. of each part of the block diagram shown in FIG. 1. Referring to this figure 2,
The operation of the screw tightening control device shown in the figure will be further explained.

FIG. 2(A) is a diagram showing the change over time of the reference signal a outputted from the speed reference circuit 1. time to
By rising at time t1, it instructs the motor 2a to start rotating, by the value of the reference signal a, instructing the rotation speed of the motor 2a, and by falling at time t1, it instructs to cut off the electric power to the motor 2a. .

FIG. 2(B) is a diagram showing the time change of the speed command signal b output from the speed command circuit 4. FIG. Time t at which the torque increase signal d is output from the time to
From time t2 when the torque increase signal d is output to time t1, the voltage is maintained at a higher voltage v1.
1 is the motor 2a when the current limiter does not operate.
proportional to the voltage applied to the In the present invention, when the voltage VQ is set to a sufficiently high value, that is, when the motor 2c is set to rotate at a sufficiently high speed, the torque up signal m is output from the torque up detection circuit 8.
It is not necessarily necessary to further increase the voltage from V■ to Vl after time t2 when is output. That is, in the case of 12, the addition circuit 3 is not necessary and the reference signal a may be used as the addition signal e.

FIG. 2(C) is a diagram showing the time change of the voltage V outputted from the power amplification circuit 5 and inputted to the motor 2a, and FIG. A diagram showing the time change of the current monitor signal C,
FIG. 2(E) is a diagram showing the change over time of the torsion angle ψ of the bit 2b with respect to the rotating shaft of the motor 2a.

As shown in FIG. 2(C), a constant voltage vo/ is applied to the motor 2a from time to when the monitor 2a starts rotating to time t3 when the screw is seated. During this time, as shown in FIG. 2(C), the current flowing through the motor 2a first flows as an inrush current at the time t4, and then a small current value is maintained until the screwing start time t4 because the torque is very small. From the start time t4 until the time t3 when the screw is seated after screwing is completed, the current value increases as the screwing load torque increases. Further, the torsion angle ψ of the bit 2b oscillates somewhat after the start of rotation at the time to, and then the torsion angle ψ temporarily settles to ψ 0. When screwing starts (time t4 above)
, the torsion angle ψ gradually increases as the torque increases until time t4 when screwing is completed.

As shown in FIG. 2(D), when screwing is completed (time t4), the torque increases rapidly, the current limiter is activated, and the current is clipped to a predetermined upper limit value i (H).
Therefore, along with this, the voltage V decreases to a somewhat lower value vz/, as shown in FIG. 2(C). Therefore, as shown in FIG. 2(E), the torsion angle ψ oscillates at a predetermined period after time t3, and reaches one period at time t2.

The flip-flop 9 shown in FIG. 1 is set at the above-mentioned time t3, and the timer 10 is set to time up at the above-mentioned time t2. Therefore, the torque increase signal d is output at the time t2, and at the time t2, the torque increase signal d shown in FIG.
), the previous upper limit value i0 is changed to a higher value tl.

As a result, the elastic force of the torsion spring 2c and the motor 2
The torque of a is added, and a force is applied to further rotate the screw in the direction of tightening. Therefore, if the time t3 is not the time when the screw is seated, the motor 2a
If this is the time when the bit 2b temporarily stops due to the torque of t2 being exceeded by the load, screwing is performed again at the time t2 to ensure that the screw is seated. This prevents the screw from being interrupted midway and the head of the screw floating.

(Effects of the Invention) As explained above in detail, the screw tightening control device of the present invention has the following advantages: When approximately one period of vibration of the torsion spring has elapsed after the current flowing through the motor of the electric screwdriver reaches the upper limit value,
Equipped with upper limit value changing means to change the above upper limit value to a higher value than the previous value, even if the bit stops temporarily due to the load as screw tightening progresses and the load increases, the screw will continue to tighten. is restarted and screwing is performed reliably.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the screw tightening control device of the present invention, and FIG. 2 is a diagram showing temporal changes in signals, etc. of each part of the block diagram shown in FIG. 1...Speed reference circuit 2a...Motor 2c...Torsion spring 3...Addition circuit 5...Power amplifier circuit l5...Upper limit value changing circuit 2...Electric driver 2b...Bit 2d...Coupling 4...Speed command circuit 6...Current limiter circuit

Claims (1)

[Scope of Claims] A screw tightening bit, a motor having a variable speed characteristic in which the rotation speed decreases as the load torque increases, and a motor disposed between the rotating shaft of the motor and the bit, and connected via a torsion spring. A screw tightening control device for controlling an electric screwdriver including a coupling that transmits rotational force of the motor to the bit, the screw tightening control device comprising: an upper limit value indicating means for indicating an upper limit value of a current flowing through the motor; a current detecting means for detecting a current to obtain a current monitor signal; and a current detecting means for limiting the current flowing through the motor so that it does not exceed the upper limit value, and adjusting a voltage according to a speed command signal instructing the rotational speed of the motor. power supply means for applying to the motor; and when approximately one cycle of vibration of the torsion spring has passed after the current flowing through the motor reaches the upper limit, the upper limit is changed to a higher value than the previous value; A screw tightening control device comprising upper limit value changing means.