JPH0696209B2 - Automatic screw tightener - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic screw tightener equipped with a reaction force type torque detection mechanism that detects a tightening torque by detecting a reaction force applied to a driver bit during tightening. .

[Prior Art] and [Problems to be Solved by the Invention] Recently, when assembling parts, tightening torque management is strictly required, and when the tightening torque is detected and reaches a predetermined tightening torque value, the motor is stopped. Many automatic screw tighteners equipped with a torque control device are used.
The torque detection mechanism of this kind of automatic screw tightening machine is provided with a strain tube for detecting a reaction force applied to the driver bit at the time of tightening and a detection resistance composed of four strain gauges attached to the strain tube and forming a bridge circuit, The reference voltage is supplied to the input end of the bridge circuit, and the amount of strain of the strain tube is detected as the amount of electricity from the output end of the bridge circuit. In addition, in this torque detection mechanism, static calibration using weights and the like is performed, and an amplification factor for zero correction and gain correction is selected by the correction unit and amplified by the amplification unit so that it is amplified from the output end of the bridge circuit. It is arranged to obtain an output signal which corresponds exactly to the torque. Furthermore, with this torque detection mechanism, malfunction of the strain gauge,
Since disconnection or the like occurs, an abnormality detection circuit for detecting the abnormality is connectable. As shown in FIG. 5, this abnormality detecting circuit is provided with the strain gauge 5b of the bridge circuit.
It has a reference resistor 5c connected in parallel with the switch 5d via a switch, and the switch 5d
The strain gauge from the output signal at the output end at this time.
Abnormality of the detection system including 5b is judged. In this type of abnormality detection circuit, because the bridge circuit is used, the output voltage at its output end is about 0.5 mV to 3 mV at full scale, which is a very small voltage compared to the input voltage applied to its input end. Has become. In order to accurately send this minute voltage to the amplification section in the subsequent stage, it is necessary to consider the resistance change due to temperature rise, the voltage drop according to the transmission distance, the influence of disturbance, etc. So these are not considered at all. Therefore, 1) The four strain gauges 5b used in the bridge circuit are of the same lot and have almost the same characteristics, so that even if the resistance increases or decreases due to temperature changes, it increases or decreases at the same rate. However, the equilibrium state of the bridge circuit is broken by connecting the reference resistors 5c having different temperature characteristics.

2) The switch 5d has a contact resistance, which not only changes depending on the temperature, the number of times of use, etc., but also a temperature imbalance occurs at both ends of the switch 5d depending on the mounting method, the mounting location, etc. of the switch 5d. Occurs.

3) By connecting the switch 5d, a part of the wiring of the bridge circuit becomes long, and not only the resistance increases, but also
It also becomes more susceptible to disturbances. Further, the twisted pair processing and the electrostatic shield processing for each of the input and output cannot be performed, and the electromagnetic and electrostatic strength cannot be increased.

There are drawbacks such as. Moreover, in this abnormality detection circuit,
I am trying to judge the malfunction of the strain gauge 5b by the amount of change appearing at the output end of the bridge circuit when the reference resistance 5c is connected, but it is judged without actually applying a load, and the strain gauge 5b malfunctions when operating. Is extremely difficult to detect. Further, since it is not possible to determine whether the bridge circuit side is abnormal or the amplifying section is abnormal, it is necessary to replace the entire torque detection mechanism, which increases the repair cost of the device.

There are drawbacks such as.

SUMMARY OF THE INVENTION The present invention is intended to eliminate the above-mentioned drawbacks, and is an automatic screw tightening capable of individually detecting not only the abnormality of the sensor unit including four detection resistors but also the abnormality of the torque detecting mechanism other than the sensor unit such as the amplifying unit. Is to provide a machine.

[Means for Solving the Problem] In order to achieve the above object, a driver base that is raised and lowered by an elevation drive source holds a driver bit that is rotatable by the rotation of a motor. A strain tube for detecting a reaction force applied to the driver bit and four detection resistors which are attached to the strain tube and constitute a bridge circuit are attached to the driver base. A first voltage supply source that supplies a first reference voltage is maintained at the input end of the bridge circuit, and a torque detection mechanism that detects the strain amount of the strain tube as an output signal obtained from the output end of the bridge circuit is configured. The output signal of the torque detecting mechanism is displayed on the display unit.

A second voltage supply source that supplies a second reference voltage in parallel with the first voltage supply source via a first switching unit is connected to an input end of the bridge circuit. The voltage supply source connected to the input terminal is configured to be switched from the first voltage supply source to the second voltage supply source.

When the control unit for operating the first switching unit detects the completion of tightening, it sends a motor stop command signal and stores the output signal of the torque detection mechanism, while sending a switching command signal to the first switching unit to send a bridge circuit. The second voltage supply source is connected to the input end of the, the output signal of the torque detection mechanism at this time is detected, and the change rate with respect to the previous output signal is compared with the change rate between the first reference voltage and the second reference voltage. Then
When these are not equal, it is configured to display an anomaly.

Further, the output signal of the bridge circuit may be amplified by the amplification unit to obtain a value that accurately corresponds to the torque. In this case, a third voltage supply source for supplying a third reference voltage is connected in parallel with the output end of the bridge circuit to the input end of the amplification unit via the second switching unit. The control unit of the second switching unit sends a switching command signal to the second switching unit to connect the third voltage supply source to the input end of the amplification unit and to detect the output signal of the torque detection mechanism. When a preset value is obtained as a value obtained from the three reference voltages, a return command signal is sent to the second switching section to operate the lifting drive source and the motor.

[Operation] In the above automatic screw tightening machine, the motor and the lifting drive source operate, and as the driver bit tightens the screw on the workpiece, the tightening torque becomes a reaction force applied to the driver bit, which is the amount of strain of the strain tube of the torque detection mechanism. As detected by the bridge circuit. This output signal is output as an output signal of the torque detection mechanism via the amplifier.

On the other hand, when tightening completion is detected by appropriate means,
The motor stop command signal is sent and the output signal of the torque detection mechanism at this time is stored. Until the motor stops, the first switching unit operates, the second voltage supply source is connected to the input end of the bridge circuit, and the output of the bridge circuit is amplified while the load is applied to the detection resistor. Detected through the section. This detection value is compared with the previous detection value, and when the change rate is equal to the change rate between the first reference voltage and the second reference voltage, the torque detection mechanism is determined to be normal, and the previous detection value is displayed. Is displayed. Then, the lifting drive source is raised to prepare for the next work.

On the other hand, when the rate of change is not equal to the rate of change between the first reference voltage and the second reference voltage, it is determined that the torque detection mechanism is abnormal, and an abnormality is displayed on the display unit.

Further, when the third reference voltage can be connected to the input terminal of the amplifying unit, when the switching command signal is sent to the second switching unit, the second switching unit operates and shuts off the bridge circuit. The third reference voltage is supplied to the input terminal of the amplifier section, and the output signal of the torque detection mechanism at this time is detected.
When the detected value is equal to the set value which is a value normally output from the amplifying unit when the third reference voltage is applied, the torque detecting mechanism after the amplifying unit is determined to be normal, and the tightening work described above is performed. . If the detected value does not reach the set value, the torque detection mechanism after the amplifier is judged to be abnormal, and the abnormality is displayed.

Embodiments Embodiments will be described below with reference to the drawings. In FIG. 1 and FIG. 2, 1 is an automatic screw tightening machine, which has a motor 2 and a driver bit 4 that receives rotation of the motor 2 via a connecting shaft 3 and rotates integrally. The motor 2 is held by a driver base 7 which is moved up and down by the operation of the lifting drive source 6 via the strain tube 5a of the torque detection mechanism 5, and the motor 2 and the lifting drive source 6 are operated to screw the driver bit 4 into a screw. When a work (not shown) is tightened on a work (not shown), a reaction force generated in the driver bit 4 according to the tightening torque rotates the strain tube 5a. A detection resistor composed of four strain gauges 5b is attached to the outer periphery of the strain tube 5a so as to form a bridge circuit. The detection resistors may not all be strain gauges. A first voltage supply source 8 for supplying a first reference voltage and a second voltage supply source 9 for supplying a second reference voltage are connected in parallel to the input terminal of the bridge circuit via a first switching unit 10. When the first switching unit 10 receives the switching command signal from the control unit 17 described later, the voltage supply source connected to the input end of the bridge circuit is switched from the first voltage supply source 8 to the second voltage supply source 9. Is configured. At the output end of the bridge circuit, an A-D converter 14 is provided via a second switching unit 11, an amplifier 12 having a correction unit 12a for selecting an amplification factor for zero correction and gain correction, and a filter 13. The output of the A / D converter 14 is connected to the input side of an I / O interface 15, which will be described later, as an output signal of the torque detection mechanism 5. The A / D conversion unit 14 includes a sample / hold circuit, and the conversion command signal and the hold command signal are configured to be sent from the control unit via the I / D interface 15. The second switching unit 11 is
When the switching command signal is received from the control unit 17, the input signal from the bridge circuit is cut off, and the third voltage supply source 16 for supplying the third reference voltage is connected to the input end of the amplification unit.

The control unit 17 of the automatic screw tightener is composed of a microcomputer, and a work start unit 18 via the I / O interface 15 and a voltage value corresponding to a desired tightening torque
A first setting unit 19 that stores the setting value, and a second setting unit that stores the rate of change between the first reference voltage and the second reference voltage as the second setting value.
The torque detection mechanism 5 is connected to the setting unit 20, the third setting unit 21 that stores the output signal normally output from the amplification unit 12 as the third setting value when the third reference voltage is applied to the amplification unit 12, and the torque detection mechanism 5. There is. Further, the control unit 17 is provided with an elevation drive source 6 for raising and lowering the driver base 7 via the I / O interface 15, and a command value is sent to the motor 2 to supply power from the power supply source 22a to the motor 2 to drive the motor 2. Connected to a motor drive unit 22 for controlling the rotation of the motor, a display unit 23 for displaying the output signal of the torque detection mechanism 5 and the presence / absence of abnormality, the A / D conversion unit 14, the first switching unit 10 and the second switching unit 11. Has been done.

Further, as shown in FIGS. 3 and 4, the control section 17: 1) When it receives a work start signal from the work start section 18, it performs an initial reset.

2) Send a switching command signal to the second switching unit 11 and send only an AD conversion command signal without sending a hold command signal.

3) The output signal of the torque detection mechanism 5 and the third signal of the third setting unit 21.
When the set values do not match, the second stitching section 11 is restored and an abnormality display command signal is sent to the display section 23.

4) The second switching unit 11 is restored, a motor drive command signal is sent to the motor drive unit 22, and a descent command signal is sent to the elevation drive source 6.

5) A hold command signal and an A-D conversion command signal are sent to the A / D converter 14 (when the hold is not necessary, the hold command signal is not transmitted).

6) Detect the completion of tightening (comparing the output signal of the AD converter 14 with the first set value stored in the first setting unit 19 as a value corresponding to the desired tightening torque, and when they do not match, 5)
Return to).

7) The output signal of the AD converter 14 is stored as the first detection value.

8) Send a motor stop command signal and a switch command signal to the first switching unit 10.

9) Sends a hold command signal and an A-D conversion command signal to the A-D conversion unit 14 and waits for the completion of the A-D conversion (when the hold is not necessary, the hold command signal is not transmitted).

10) The output signal of the AD converter 14 is stored as the second detection value.

11) Wait for the motor 2 to stop.

12) The rate of change is calculated from the first detected value and the second detected value, and compared with the second set value of the second setting unit 20 stored as the rate of change between the first reference voltage and the second reference voltage. , When both do not match, an NG display command signal is sent to the display unit 23 and the process jumps to 14).

13) Send an OK display command signal to the display unit 23.

14) Send the display command signal of the first detection value to the display unit 23.

15) The first switching unit 10 is restored, and a rising command signal is sent to the lifting drive source 6.

16) It is configured to operate in the end operation sequence.

In the above automatic screw tightener, when the work start signal is transmitted from the work start unit 18, the second switching unit 11 is activated after the initial reset, and the third end is provided at the input end of the amplification unit 12 of the torque detection mechanism 5. The reference voltage is connected. At the same time, A
-A hold command signal is not sent to the D conversion unit 14, and A-
Only the D conversion command signal is transmitted, and the third reference voltage is amplified.
The third set value stored as a value normally output from the amplifier 12 when applied to the input terminals of 12 and the output signal of the AD converter 14 are compared. When the two do not match, it is determined that the torque detecting mechanism 5 after the amplifying unit 14 is abnormal, and after the second switching unit 11 is restored, an abnormal display is displayed on the display unit 23.

On the other hand, when the output signal matches the third set value, it is determined that the torque detection mechanism 5 is normal, the second switching unit 11 returns, and then the motor 2 is driven and the vertical movement is performed. The drive source 6 operates, the driver base 7 descends,
The screw at the tip of the driver bit 4 is tightened on the work.

As the screw is tightened on the work, the tightening torque applied to the screw is applied to the strain tube 5a as a reaction force applied to the driver bit 4, and the amount of strain is detected by the strain gauge 5b forming the bridge circuit. During this time, at the same time as the motor 2 is driven, the hold command signal and the A-D conversion command signal are sent to the A-D converter 14, and the output signal is compared with the first set value corresponding to the desired tightening torque. It When they do not match each other, the hold command signal and the A / D conversion command signal are immediately transmitted to the A / D conversion unit 14, and the comparison is repeated.

When the output signal matches the first set value and the tightening completion is detected, the detected value at this time is stored as the first detected value, and the stop command signal is sent to the motor 2. Furthermore, the first
A switching command signal is sent to the switching unit 10, the second reference voltage is connected to the input end of the bridge circuit, and A-
A hold command signal and an A-D conversion command signal are sent to the D conversion unit 14. The output signal of the AD converter 14 at this time is stored as the second detection value, and the motor 2 is stopped.
At this time, the total time of the switching time of the first switching unit 10, the hold command time, the AD conversion time, and the time required to store the second detected value is greater than the time required until the motor 2 completely stops. Short enough.

When the motor 2 is stopped, the rate of change is calculated from the first detection value and the second detection value, and the rate of change is the second rate of change between the first reference voltage and the second reference voltage. The second set value stored in the setting unit 20 is compared. In this case, since the output signal of the strain gauge 5b is detected with the load applied to the strain gauge 5b, the malfunction of the strain gauge 5b can be accurately checked.

When the rate of change and the second set value do not match, it is determined that the strain gauge 5b is malfunctioning, an NG display is displayed on the display unit 23, and the torque at that time is displayed on the display unit 23.

On the other hand, when the rate of change matches the second set value, the strain gauge 5b is determined to be normal, an OK display is displayed on the display unit 23, and the first detected value is displayed on the display unit 23. .

After that, after the first switching unit 10 returns, the elevating drive source 6 operates, the driver base 7 rises, the original position is restored, and all the operations are completed.

[Effects of the Invention] As described above, according to the present invention, two reference voltages are alternately applied to the input end of the bridge circuit composed of four detection resistors attached to the strain tube for detecting the reaction force applied to the driver bit. Since it is configured so that it can be connected, another reference voltage is connected to the input end of the bridge circuit when tightening completion is detected, and the detection resistance is actually loaded by comparing the change rate at that time with the change rate of the reference voltage. There is an advantage that the operation failure of the detection resistor can be checked in the state where the voltage is added, and more than that can be accurately detected. Further, according to the present invention, before driving the motor, another reference voltage is connected to the input end of the amplification section of the torque detection mechanism, and the output signal of the torque detection mechanism at that time is applied to the input end of the amplification section by the reference voltage. When the two values match, the torque detection mechanism after the amplifier is judged to be normal, If the two do not match, the torque detection mechanism is determined to be abnormal,
There is an advantage that it is possible to display an abnormality, and moreover, it is possible to immediately judge whether or not the abnormality of the sensor portion formed of the detection resistance or the abnormality of the torque detection mechanism other than that.

Further, according to the present invention, the abnormality can be detected without incorporating an extra element in the bridge circuit, and the minute voltage can be accurately detected without receiving any noise at the time of extracting the minute voltage, which enables accurate abnormality determination. And so on.

Although the torque detection mechanism is checked every time the tightening work is performed in the embodiment, the torque detection mechanism may be checked at a predetermined cycle. Further, in the embodiment, the completion of tightening is obtained from the output signal of the torque detection mechanism, but if the rotation of the motor is used a differential speed reducer such as a differential planetary mechanism, the completion of tightening is detected by detecting the stop of the driver bit. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining the whole of the present invention, FIG. 2 is a circuit diagram of a main part of a torque detection mechanism according to the present invention, FIG. 3 is a flow chart for explaining the operation of a control unit according to the present invention, and FIG. FIG. 5 is a flowchart for detecting the completion of tightening, and FIG. 5 is a circuit diagram of a main part of a conventional torque detecting mechanism. 1 ... Automatic screw tightener, 2 ... Motor, 3 ... Connecting shaft, 4 ... Driver bit, 5 ... Torque detection mechanism, 5a ... Strain tube, 5b ... Strain gauge, 5c ... Reference resistance, 5d ... switch, 6 ... elevation drive source, 7 ... driver base, 8 ... first voltage supply source, 9 ... second voltage supply source, 10 ... first switching section, 11 ... second switching Section, 12 ... amplifying section, 12a ... correcting section, 13 ... filter, 14 ... A / D converting section, 15 ... I / O interface, 16 ... third voltage supply source, 17 ... control section , 18 ... Work start part, 19 ... First setting part, 20 ... Second setting part, 21 ... Third setting part, 22 ... Motor drive part, 22a ... Power supply part, 23 ... Display Department,

Claims (2)

[Claims] 1. A strain tube and a strain tube for holding a rotatable driver bit by a rotation of a motor on a driver table which is moved up and down by a lifting drive source and detecting a reaction force applied to the driver bit on the driver table. A reaction force type torque detection mechanism having four detection resistors attached to the bridge circuit and connected to a first voltage supply source for supplying a first reference voltage to the input end of the bridge circuit, The strain amount of the strain tube obtained from the output end of the bridge circuit is detected as an output signal of the torque detection mechanism, and when the completion of tightening is detected, a motor stop command signal is sent and the output signal of the torque detection mechanism is displayed on the display unit. In an automatic screw tightener equipped with a control unit, a second voltage supply for supplying a second reference voltage in parallel with a first voltage supply source connected to an input end of a bridge circuit. A power supply is connected and a first switching unit that switches the voltage supply source connected to the input end of the bridge circuit from the first voltage supply source to the second voltage supply source is connected, while the motor stop command signal is detected when tightening completion is detected. And the output signal of the torque detection mechanism is stored, and a switching command signal is further sent to the first switching unit to connect the second voltage supply source to the input end of the bridge circuit to output the output signal of the torque detection mechanism at this time. When the rate of change with respect to the output signal detected last time is not equal to the rate of change of the first reference voltage and the second reference voltage,
An automatic screw tightener, which is equipped with a control unit that displays an error. 2. A strain tube and a strain tube for holding a rotatable driver bit by a rotation of a motor on a driver table which is elevated and lowered by an elevation drive source and detecting a reaction force applied to the driver bit on the driver table. A reaction force type torque detection mechanism having four detection resistors attached to the bridge circuit and connected to a first voltage supply source for supplying a first reference voltage to the input end of the bridge circuit, The amount of strain of the strain tube is detected from the output end of the bridge circuit as an amount of electricity, and this is amplified by the amplifier to be the output signal of the torque detection mechanism. When the completion of tightening is detected, a motor stop command signal is sent and the torque is detected In an automatic screw tightener equipped with a control unit for displaying the output signal of the mechanism on the display unit, the input of the amplifier is connected to the bridge circuit via the second switching unit. An output terminal and a third voltage supply source for supplying a third reference voltage are connected in parallel, and a switching command signal is sent to the second switching section to connect a third voltage supply source to the input terminal of the amplification section, When the output signal of the torque detection mechanism at this time has a value preset as a value obtained from the third reference voltage, a control unit that sends a return command signal to the second switching unit and operates the lifting drive source and the motor An automatic screw tightener characterized by the provision of.