JPH02232127A - Automatic thread fastening machine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an automatic system equipped with a reaction-type torque detection mechanism that detects the reaction force applied to the driver bit during tightening (month to torque). Regarding screw tightening machines.

[Prior art] L6' [Zenmei A... Many automatic screwdrivers are in use that are equipped with a torque control device that stops the motor. The torque detection mechanism of this type of automatic screw tightening system is used for tightening (
It is equipped with a strain tube that detects the reaction force applied to the driver bit during operation, and a detection resistor consisting of four strain gauges attached to the strain tube and forming a bridge circuit, and supplies a reference voltage to the input terminal of the bridge circuit. The strain rate of the strain tube is then detected as an electrical quantity from the output end of the bridge circuit. In addition, this torque detection mechanism performs static calibration using a weight, etc., selects the amplification factor for zero correction and gain correction in the correction section, and amplifies it in the amplification section. The configuration is such that an output signal that accurately corresponds to the torque is obtained. Further, in this torque detection mechanism, malfunction of the strain gauge, disconnection, etc. may occur, so an abnormality detection circuit for detecting such abnormality is connectable. As shown in FIG. 5, this abnormality detection circuit has a reference resistor 5C connected in parallel with one of the strain gauges 5b of the bridge circuit via a switch 5d. In addition, the switch 5d is operated while the reference voltage is supplied to the input end of the bridge circuit, and an abnormality in the detection system including the strain gauge 5b is determined from the output signal at the output end at this time.

This type of abnormality detection circuit uses a bridge circuit, so the output voltage at each output terminal is 0.5 at full scale.
...V to about 3 mV, which is a very small voltage compared to the input voltage applied to its input terminal. In order to accurately send this minute voltage to the subsequent amplifier section, it is necessary to take into account resistance changes due to temperature rise, voltage drops depending on the transmission distance, and the effects of disturbances, etc. These things are not taken into consideration at all. Therefore, 1
》The four strain gauges 5b used in the bridge circuit are from the same batch] 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. By connecting reference resistors 5C having different temperature characteristics, the equilibrium state of the bridge circuit is disrupted.

2) The switch 5d has contact resistance, and not only does this change depending on the temperature, number of times of use, etc., but also temperature imbalance occurs at both ends of the switch 5d depending on the mounting method and mounting location of the switch 5d, which causes thermoelectromotive force. occurs.

3) By connecting the switch 5d, a portion of the wiring in the bridge circuit becomes longer, which not only increases the resistance but also becomes more susceptible to external disturbances. In addition, twisted bare processing and electrostatic shielding processing for each input and output cannot be performed, and it cannot be made electromagnetically and electrostatically strong.

There are some disadvantages such as: Also, in this abnormality detection circuit,
An attempt is made to determine whether the strain gauge 5b is malfunctioning based on the amount of change that appears at the output end of the bridge circuit when the reference resistor 5C is connected, but the determination is made without actually applying any load, and the malfunction during the operation of the strain gauge 5b is determined. is extremely difficult to detect. Furthermore, it is not possible to determine whether the problem is in the bridge circuit or in the amplification section, and the entire torque detection mechanism must be replaced, which increases the cost of repairing the device.

There are some disadvantages such as:

The present invention aims to eliminate the above-mentioned drawbacks, and is an automatic screw tightening system that can individually detect abnormalities in the torque detection mechanism other than the sensor part, such as the amplifier part, as well as abnormalities in the sensor part made up of four detection resistors. The aim is to provide an opportunity.

[Means for Solving the Problems] In order to achieve the above object, a driver bit that is rotatable under the rotation of a motor is held on a driver stand that is raised and lowered by a gastrointestinal drive source. A strain tube for detecting the reaction force applied to the driver bit and four detection resistors attached to the strain tube and forming a bridge circuit are attached to the driver stand. At the input end of the bridge circuit,
A first voltage supply source supplying a first reference voltage is connected, and a voltage detection mechanism is configured to detect the distortion of the strain tube as an output signal obtained from the output end of the bridge circuit. The output signal of the torque saving mechanism is configured to be displayed on the display section.

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

When the control unit that operates the first switching unit detects the completion of tightening, it sends a motor stop command signal, stores the output signal of the torque detection mechanism, and sends a switching command signal to the first switching unit to activate the bridge circuit. A second voltage supply source is connected to the input terminal of the 1 to 1 torque detection mechanism at this time, and the rate of change with respect to the previous output signal is determined as the rate of change between the reference voltage and the second reference voltage. compared to
It is configured to display an abnormality when these are not equal.

Further, the output signal of the bridge circuit may be amplified by an amplification section, and the output signal may be configured to be 11 to a value that accurately corresponds to the torque. In this case, a third voltage supply source that supplies a third reference voltage is connected to the input end of the amplification section in parallel with the output end of the bridge circuit via a second switching section. The control unit of the second switching unit sends a switching command signal to the second switching unit to connect a third voltage supply source to the input terminal of the amplification unit, and detects the output signal of the torque detection mechanism. When a preset value is obtained as the value obtained from the third reference voltage, a return command signal is sent to the second switching section to operate the lifting drive source and the motor.

In the automatic screw tightening machine described above, the motor and lifting drive source operate, and as the driver bit tightens the screw onto the workpiece, the tightening torque becomes a reaction force applied to the driver bit, and this is the amount of strain in the strain tube of the torque detection mechanism. detected by the bridge circuit. This output signal is outputted as an output signal of the torque detection mechanism via the amplification section.

On the other hand, if the completion of tightening is not detected by an appropriate means,
At the same time as the motor stop command signal is sent, 1~
The output signal of the torque detection mechanism is stored.

Until the motor stops, the first switching section is activated, the second voltage supply source is connected to the input terminal of the bridge circuit, and the output of the bridge circuit is amplified with a load applied to the detection resistor. detected through the If this detected value and the previous detected value are not compared and the rate of change is equal to the rate of change between the first reference voltage and the second reference voltage, the torque detection mechanism is determined to be normal, and the previous detected value is displayed on the display. is displayed.

After that, the lifting drive source is raised to prepare for the next work.

On the other hand, if 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 section.

In addition, when a third reference voltage can be connected to the input terminal of the amplifying section, when a switching command signal is sent to the second switching section, the second switching section operates to cut off the bridge circuit. A third reference voltage is supplied to the input end of the amplification section, and the output signal of the torque detection mechanism at this time is detected.

If this detected value is equal to the set value, which is the value that is normally output from the amplification section when the third reference voltage is applied, it is determined that the 1 to 1 torque detection mechanism after the amplification section is normal, and the above-mentioned tightening work is performed. It will be done. Further, if the detected value does not reach the set value, it is determined that the torque detection mechanism after the amplification section is abnormal, and the abnormality is displayed.

[Example] Hereinafter, an example will be described based on the drawings. 1 and 2, reference numeral 1 denotes an automatic screw tightening machine, which has a motor 2 and a driver bit 4 that rotates integrally with the rotation of the motor 2 via a connecting shaft 3. This motor 2 is held on a driver stand 7 which is raised and lowered by the operation of an elevating drive source 6 via a strain tube 5a of a torque detection mechanism 5, and when the motor 2 and elevating drive source 6 are operated, the driver bit 4 is When a screw (not shown) is tightened to a workpiece (not shown), a reaction force generated in the driver bit 4 according to the tightening torque rotates the strain tube 5a. A detection resistor consisting of four strain gouges 5b is attached to the outer periphery of the strain tube 5a so as to constitute a bridge circuit. This sensing resistor does not need to be entirely composed of strain gauges.

A first voltage supply source 8 that supplies a first reference voltage and a second voltage supply source 9 that supplies a second reference voltage are connected in parallel to the input end of the bridge circuit via a first switching unit 10. When this first switching unit 10 receives a switching command signal from a 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. It is composed of

Further, at the output end of the bridge circuit, a second switching section 11, an amplification section 12 including a correction section 12a for selecting an amplification factor for zero correction and gain correction, and a filter 13 are provided.
The A-D converter 14 is connected via the A-D converter 14.
The output of the D converter 14 is configured to be sent as an output signal of the torque detection mechanism 5 to the input side of an I/O interface 15, which will be described later. The A/D converter 14 includes a ripple/hold circuit, and is configured such that a conversion command signal and a hold command signal are sent from the control unit via the I/O interface 15. When the second switching section 11 receives a switching command signal from the control section 17, the input signal from the bridge circuit is cut off, and the third voltage supply source 1 supplies a third reference voltage to the input end of the amplification section.
6.

The control unit 17 of the automatic screw tightening machine is a microcomputer, and controls a work start unit 18 via an I/O interface 15 and a first setting which stores a voltage value corresponding to a desired tightening torque as a first setting value. A second setting section 20 stores the rate of change between the first standard voltage and the second reference voltage as a second setting value, and a normal output from the amplification section 12 when the third reference voltage is applied to the amplification section 12. a third setting unit 21 that stores the output signal as a third setting value;
・The power detection structure 5 is connected. The control unit 17 also includes a lifting drive source 6 that lifts and lowers the driver stand 7 via an I/O interface 15, and a lifting drive source 6 that sends a command value to the motor 2 and supplies power to the motor 2 from a power supply source 22a. A motor drive section 22 that controls the rotation of the torque detection mechanism 5, a display section 23 that displays the output signal of the torque detection mechanism 5 and the presence or absence of an abnormality, the A-D conversion section 14, the first switching section 10, and the second switching section 11 are connected. It's worn out.

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

2) While sending a switching command signal to the second switching unit 11, only an A-D conversion command signal is transmitted without transmitting a hold command signal.

3》When the output signal of the torque detection mechanism 5 and the 3rd E9 constant value of the 3rd setting part 21 do not match, the 2nd switching part 11
At the same time, the abnormality display command signal is sent to the display section 23.
send to

4) Return the second switching unit 11, send a motor drive command signal to the motor drive unit 22, and further send a lowering command signal to the lifting drive source 6.

5) Hold command signal and A-D converter 14
Send a conversion command signal (do not send a hold command signal when there is no need to hold).

6) Detecting completion of tightening (first setting unit 1 as a value corresponding to the output signal of the A-D converter 14 and the desired tightening torque)
9, and if they do not match,
Return to 5》.

7) Store the output signal of the A-D converter 14 as the first detected value.

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

9) Hold command signal and A-D converter 14
Send a conversion command signal and wait for the completion of A-D conversion (do not send a hold command signal when there is no need to hold)
.

10) Store the output signal of the A-D converter 14 as a second detected value.

1 1) U: Has 2 stops overnight.

12 >> Calculate the rate of change from the first detected value and the second detected value, and compare it with the second setting value of the second setting unit 20 stored as the rate of change between the first reference voltage and the second reference voltage. , when the two do not match, sends an NG display command signal to the display section 23, and displays 1.
Jump to 4).

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

14) Send a display command signal of the first detected value to the display section 23.

15>Resetting the first switching unit 10 and
A lift command signal is sent to the lift drive source 6.

16) End The system is configured to operate in the following operating order.

In the automatic screw tightening machine described above, when the work start signal is transmitted from the work start part 18, the second switching part 11 is activated after initial reset i~, and the torque detection mechanism 5
A third reference voltage is connected to the input terminal of the amplifying section 12 . At the same time, no hold command signal is transmitted to the A-D converter 14, only the A-D conversion command signal is transmitted, and when the third reference voltage is applied to the input terminal of the amplifying unit 12, the amplifying unit 12 normally The third setting value stored as the value to be output from A
-The output signal of the D converter 14 is compared. When the two do not match, it is determined that the torque detection mechanism 5 after the amplification section 14 is abnormal, and after the second switching section 11 is reset, an abnormality display is displayed on the display section 23.

On the other hand, if the output signal and the third set value match, it is determined that the torque detection mechanism 5 is normal, and after the second switching section 11 returns, the motor 2 is driven and the The drive source 6 is activated, the driver stand 7 is lowered, and the screw at the tip of the driver bit 4 is tightened to the workpiece.

As the screw is tightened to the workpiece, the torque applied to the screw is applied to the strain tube 5a as a reaction force applied to the driver bit 4, and the strain is detected by the strain gauge 5b forming a bridge circuit. During this time, at the same time as the motor 2 is driven, a hold command signal and an A-D conversion command signal are sent to the A-D converter 14, and the output signal and the first set value corresponding to the desired tightening torque are compared. It will be done.

When the two do not match, the A-D converter 14 immediately receives a hold command signal and A-D! A conversion command signal is issued and the comparison is repeated.

When the output signal and the first set value match and completion of tightening is detected, the detected value at this time is stored as the first detected value, and a 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 terminal of the bridge circuit, and the A
A hold command signal and a Δ-D conversion command signal are sent to the -D converter 14. The output signal of the A-D converter 14 at this time is stored as the second detection value, and the motor 2 is waited for to stop. At this time, the sum W1 time of the switching time of the first switching unit 10, the hold command l4 period, the A-D conversion time, and the time required to store the second detected value is the time required for the motor 2 to completely stop. is sufficiently shorter than .

When the -E meter 2 stops, the rate of change is calculated from the first detected value and the second detected value, and this rate of change is calculated from the first reference voltage and the second reference voltage. is compared with the second set value stored in the second setting section 20 as the rate of change of the strain gauge 5b. It is possible to accurately check for malfunctions.

When the rate of change does not match the second set value, it is determined that the distortion gouge 5b is malfunctioning, and an NG display is displayed on the display section 23.
The torque at that time is further displayed on the display section 23.

On the other hand, when the rate of change and the second set value match, the distortion gouge 5b is determined to be normal, an OK display is displayed on the display section 23, and the first detected value is displayed on the display section 23.
It will be displayed.

Thereafter, after the first switching unit 10 returns, the elevating drive source 6 is activated and the driver stand 7 is raised and returned to its original position, completing the entire work.

[Effects of the Invention] As explained above, the present invention alternately applies two reference voltages to the input terminal of a bridge circuit consisting of four d1 resistors attached to a strain tube that detects the reaction force applied to the driver bit. Since it is configured so that it can be connected to the input terminal of the bridge circuit when detecting the completion of tightening, the rate of change at that time is compared with the rate of change of the reference voltage to determine the actual voltage applied to the detection resistor. There are advantages such as being able to check for malfunction of the detection resistor under load and accurately detecting the abnormality. Furthermore, before driving the motor, another reference voltage is connected to the input terminal of the amplification section of the torque detection mechanism, and the reference voltage is applied to the output signal of the torque detection mechanism at that time to the input terminal of the amplification section. The structure is configured so that when the output is normal, the setting value is compared with a set value stored in advance as the value output from the amplifying section when normal.When the two match, it is determined that the torque detection mechanism after the amplifying section is normal, and the normal If the above-mentioned two do not match, it is determined that the torque detection mechanism is abnormal and an abnormality display can be performed, and it is possible to determine whether the sensor unit consisting of the detection resistor is abnormal or something else. It has the advantage that it can be immediately determined whether there is an abnormality in the torque detection mechanism.

Furthermore, the present invention can detect abnormalities without incorporating any extra elements into the bridge circuit, and can accurately detect minute voltages without receiving any noise when extracting minute voltages, making it possible to accurately determine abnormalities. There are advantages such as

In the embodiment, the torque detection mechanism is checked every time a tightening operation is performed, but it can also be configured to be checked at predetermined intervals. In addition, in the embodiment, the completion of tightening is determined at 1q from the output signal of the torque detection mechanism, but if a differential reduction gear such as a differential planetary mechanism is used to rotate the motor, completion of tightening can be detected by detecting the stoppage of the driver bit. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram explaining the entirety of the present invention, FIG. 2 is a main circuit diagram of the torque detection mechanism according to the present invention, FIG. 3 is a flowchart explaining the operation of the control section according to the present invention, and FIG. The figure is a flowchart for detecting completion of tightening.
The figure is a circuit diagram of a main part of a conventional torque detection mechanism. Automatic screw tightening machine, 2 motor, connecting shaft, 4 driver bit, 1~luke detection mechanism, 5a strain tube, strain gauge,
5C reference resistance, switch, 6 lifting drive source, driver stand, 8 first voltage supply source, second voltage supply source, 10 first switching section, second switching section, 12 amplification section, correction section,
13 Filter, A-D converter, 15 I/O interface, third voltage supply source, 17 Control unit,
Work start part, 19 first setting part, second setting part, 21 third setting part, motor drive part,
22a power supply section, display section,

Claims (1)

[Scope of Claims] 1) A driver stand that is raised and lowered by an elevating drive source holds a driver bit that is rotatable under the rotation of a motor, and a strain tube that detects a reaction force applied to the driver bit on this driver stand; A reaction force type torque detection mechanism is attached to this strain tube and includes four detection resistors that constitute a bridge circuit, and a first voltage supply source that supplies a first reference voltage is attached to the input end of this 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. In an automatic screw tightening machine equipped with a control unit indicated by A first switching unit is connected to switch the voltage supply source connected to the input end of the circuit from the first voltage supply source to the second voltage supply source, while sending a motor stop command signal when tightening completion is detected and outputting the torque detection mechanism. The signal is memorized, and a switching command signal is sent to the first switching section, a second voltage supply source is connected to the input end of the bridge circuit, the output signal of the torque detection mechanism at this time is detected, and the output signal is compared to the previous output signal. When the rate of change is not equal to the rate of change between the first reference voltage and the second reference voltage,
An automatic screw tightening machine characterized by being equipped with a control section that displays an abnormality display. 2) A driver stand that is raised and lowered by an elevating drive source holds a driver bit that can freely rotate under the rotation of a motor, and a strain tube that detects the reaction force applied to the driver bit on this driver stand, and a strain tube that is attached to the strain tube. In addition, a reaction force type torque detection mechanism equipped with four detection resistors constituting a bridge circuit is installed, and a first voltage supply source that supplies a first reference voltage is connected to the input terminal of this bridge circuit. The amount of distortion is detected as an electrical amount from the output end of the bridge circuit, and this is amplified by the amplifier section to become the output signal of the torque detection mechanism. When the completion of tightening is detected, a motor stop command signal is sent and the output of the torque detection mechanism is In an automatic screw tightening machine equipped with a control unit that displays a signal on a display unit, a third voltage supply source supplies an output terminal of the bridge circuit and a third reference voltage to an input terminal of the amplifier unit via a second switching unit; are connected in parallel, a switching command signal is sent to the second switching section, and a third voltage supply source is connected to the input terminal of the amplification section, so that the output signal of the torque detection mechanism at this time is the third voltage supply source.
An automatic screw tightening machine characterized by comprising a control section that sends a return command signal to the second switching section and operates an elevating drive source and a motor when a preset value is taken as the value obtained from the reference voltage. .