JPH01301027A - Screw tightening device - Google Patents

Abstract

PURPOSE:To improve the accuracy of torque by controlling a motor through a seat detection circuit based on the rotation and current of the motor, a reverse rotation brake circuit and a CPU for performing PWM control. CONSTITUTION:Rotation of a motor driver motor 12 detected through a detector 13 is fed through a control circuit 10 and a speed detection set detection circuit 7 to a control CPU 1 while current variation is fed through a detector 11 and a conversion circuit 6 to the control CPU 1. When seating is detected, a power transistor 9 is PWM controlled through a chopper power source circuit 4 and the control circuit 10. At first, a reverse brake command is fed to the control circuit 10 for a set time than a first low tightening torque current is fed for a predetermined time corresponding to the type of work and screw thereafter it is increased gradually to supply set torque current to the motor 12. By such arrangement, accuracy of torque can be improved and screw tightening can be carried out over a widened torque control range.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a screw tightening device that is capable of tightening various screws such as machine screws, wood screws, self-tapping screws, etc. with a wide range of torque with high precision and at high speed. It is.

BACKGROUND OF THE INVENTION In recent years, screw tightening work has become more demanding due to the diversification of screws such as microscrews and the appearance of various workpieces, and high quality screw tightening work with high torque accuracy and a wide torque range.

The screw tightening operation using the above-mentioned conventional electric screwdriver will be described below with reference to the drawings. FIGS. 5 and 6 show examples of conventional electrically controlled electric screwdrivers. In FIG. 5, 60 is a rectifier. Reference numeral 61 is a power transistor (hereinafter referred to as power Tr) which controls the mist output of the motor. 62 is the driver motor, 6
3 is a detection resistor for detecting the current flowing through the motor, 64 is a volume for adjusting the current judgment level, e5 is a comparison/determination device thereof, and 66 is a transistor for driving the power transistor. In FIG. 5, 67 indicates an example of the current flowing through the motor;
8 is a judgment level, and 69 is a screw tightening completion level.

The operation of the electric screwdriver configured as above will be described below. First, power is supplied to the motor 62 by a start signal given to the puff Tr 61, and the motor starts rotating. Then, the current that flows through the motor draws a curve like 67, and at startup 1'lOT + steady time T2, the rear screw is shielded against the workpiece, and the current increases.e
When the value matches the value 68 set by the level adjustment volume 4, the comparator 65 operates, and the power transistor is turned off by the drive transistor 66, but due to the inertia, the comparator 65 operates.
When it reaches level 9~, the motor stops and the screw tightening is completed.

As another conventional example, FIGS. 7 and 8 show examples of conventional mechanically controlled electric screwdrivers, in which 7o is a motor, 71 is a driving cam, 72 is a driven cam, 7
3 is a tightening bit, 74 is a torque spring, 76 is a limit switch, and 76 is a screw.

The operation of the mechanical electric screwdriver configured as described above will be described below. Electric power is supplied to the motor 7o in FIG. 7 in the circuit shown in FIG. 8, the motor rotates, and the screws are tightened through the pit 73. When the screw 76 is seated on the workpiece and the torque value set by the torque spring 74 is reached, the driving cam 1 and the driven cam 72 are placed on the top of each cam as shown in FIG. , the limit switch 76 operates to turn off the power to the motor, and the screw tightening is completed.

Problems that the invention sought to solve However, in the above two conventional configurations, it is very difficult to determine the level in a short time when the motor rotates at high speed even with an electrical method, and to stop the motor without inertia of the motor and gear. There were large variations in the values, and even with mechanical methods it was difficult to set fine torque values or control a wide torque range, and there were also major mechanical problems such as noise and longevity.

In view of the above-mentioned problems, the present invention is an electric screwdriver screw tightening control that controls a motor rotating at high speed, accurately tightens screws with a set torque, and can display and output torque value data to the outside. equipment.

Means for Solving the Problems and the technical means of the present invention for solving the above-mentioned problems are a seating detection circuit for a high-speed rotating electric screwdriver motor, a reversing brake circuit for removing inertia of the motor and gears, and a screw torque control circuit with high accuracy. , and is configured so that screws can be tightened with a wide range of torque. In addition, the power supply and motor drive circuit are controlled by PWM (Pulse Wide Modulation, hereinafter referred to as PWM) while feeding back the current flowing to the motor.
This system includes a control circuit (abbreviated as ``3''), an input circuit for externally selecting a screw tightening pattern according to the screw and workpiece, and a circuit for displaying and outputting screw tightening torque data.

For production The effect of this technical means is as follows.

The faster the motor rotates, the greater the change from rotation to stop. Therefore, seating can be detected in a very short time, and the reverse braking circuit, which also includes current limiting, allows tightening by inertia. Thereafter, by controlling the power supply and the power transistor, no inertia is generated even when the screw tightening is completed after reaching the second final setting torque, and accurate screw tightening can be realized.

Example An embodiment of the present invention will be described below based on the accompanying drawings.

FIG. 2 is a circuit block diagram of the screw tightening control device in the first embodiment of the present invention.

In FIG. 2, 1 is a control CPU, 2 is an RO containing control software and screw tightening patterns, and 3 is a RAM for storing screw tightening conditions. 4 is chopper type power supply section,
5 is an analog-to-digital converter (hereinafter referred to as an A/D converter), 6 is a current detection conversion circuit, and 7 is a speed detection/seating detection circuit. 8 is part of the motor driver and has a power transistor inside.
9. Puff-Tr control circuit 10. Includes current detection 11, etc.

12 is an electric driver motor, and 13 is a rotation detector. 14 is a display unit for screw tightening torque values, tightening conditions, etc., 15 is a switch for data input/operation, and 16 is an interface circuit for connection with external equipment (hereinafter referred to as I/F), which displays start/screw tightening conditions 17, etc. Received, completed/defective/
A signal 18 such as torque data is output. 19 is a command signal to the chopper type power supply, 20 is an output voltage to the electric driver motor, and 21 is a control signal and a brake signal for the power Tr that drives the electric driver motor.

The operation of the screw tightening control device configured as described above will be explained with reference to FIGS. 2, 3, and 4.

FIG. 3 shows the curve of the current flowing through the electric driver motor, and its value is measured by the current detector 11. A current detection conversion circuit e is read in by the A/D converter 5, and the speed fluctuation is also detected by the rotation detector 13 in FIG. 2.The seating detection circuit detects the speed.

The signal is read through the A/D converter 5 and performs PWM control on the chopper type power supply section 4 and the puff transistor 9.

When the motor was started, a starting current 22 in Fig. 2 flowed.
After the screw 3o is screwed into the workpiece 23, the tightening bit 29 tightens the screw 3o into the workpiece 1 as shown in FIG. 4(a).
32, the positional relationship between the focus 29 and the screw 3o becomes as shown in FIG. 4(b), and the current changes as shown at the inflection point 24 in FIG.

This displacement is detected by the rotation detector 13 in FIG. By reading word of mouth information from the speed detection seating detection circuit 7 and changes in current from the current detector 11° current detection conversion circuit 6, the CPU 1
When the reverse brake command is output to the control circuit 1o for 11 hours and the motor current is limited, the brake current 26 shown in Figure 2 flows for the set time, and the positional relationship between the bit and screw at that time is as shown in Figure 1 (C). It becomes like this. Next, after the set time, a shock is applied when the bit 29 hits the screw 3o again as shown in FIG. It outputs for t2 hours so that it does not occur. Next, the torque of the electric screwdriver motor is gradually increased as a current as shown by a curve 27, and the electric screwdriver motor is driven for a time t3 at a set torque current value 28, and then stopped so that there is no inertia in the motor and gear. This completes screw tightening.

Effects of the Invention As described above, the present invention provides a rotation detection mechanism in an electric screwdriver motor for tightening screws, a circuit for detecting seating of a screw on a workpiece based on a rotation detection signal of the motor and a current flowing through the motor, and a reversal brake circuit based thereon. By controlling the motor by providing a chopper type power source and PWM control using the CPU of the power Tr, it is possible to realize an electric screwdriver for tightening screws with significantly improved torque accuracy and an expanded torque control range.

[Brief explanation of the drawing]

Fig. 1 is a front view of a screw tightening device using a servo motor to speed up the vertical movement of an electric screwdriver, Fig. 2 is a tightening control circuit diagram of the screw tightening device in the first embodiment of the present invention, and Fig. 3 is a current curve diagram of the electric screwdriver motor according to the circuit shown in Fig. 2, Fig. 4(a) is a cross-sectional view of the workpiece showing the state in which the screw is seated on the workpiece, Fig. 4(b),
(C) and (d) are plan views of the screw, Figure 5 is an electric circuit diagram of a conventional screw tightening device, Figure 6 is a current curve diagram of the same, and Figure 7 is a cross section of a bit showing the conventional mechanical configuration. FIG. 8 is an electric circuit diagram of the same, and FIG. 9 is a block diagram of another embodiment. 12... Electric driver motor, 30...
...Screw, 41...Servo motor for head up and down. Name of agent: Patent attorney Toshio Nakao and one other personjf
-D 1 hook 79 35~-Ishishiri'l1yq 36---Fixed/R router' 37---Universal button 1 Inlet 33・-7-ri 2 □ Fig. 5 Fig. 7

Claims (6)

[Claims] (1) Consists of a screwdriver capable of tightening a screw, a drive unit that drives this driver, and a control unit that controls this drive unit, and the control unit sends a detection signal that detects rotation of the drive unit and a drive unit The start of screw tightening is detected from the current signal that detects the current flowing through the screw, and reverse braking and current restriction are applied to the drive part for a certain period of time to remove inertia in the motor and gear part. A screw tightening device configured to drive at a low torque, then gradually increase the current in the drive section again, and then tighten the screw to a preset torque value. (2) Claim 1, characterized in that the power applied to the motor and the drive pulses applied to the power transistor that drives the motor are controlled by pulse wide modulation so as to tighten the screw with a preset torque value. Screw tightening device as described. (3) The screw tightening device according to claim 1, wherein the means for moving the electric screwdriver to the tightening position comprises a robot and a servo motor for vertical movement mounted on the tip of the robot to speed up the movement. (4) A fixed type screw tightening device according to claim 1, wherein the means for vertically moving the electric screwdriver to the tightening position is a servo motor. (5) Claim 1 is provided with a display that simply displays the torque value for screw tightening using the current flowing through the electric screwdriver, or a function of transmitting data to a printer or personal computer using a communication means. Screw tightening device. (6) The screw tightening device according to claim 5, which is configured to be able to display torque values, deviations, maximum values, minimum values, etc. based on the torque values detected by the sensor.