JPS59196134A - Screw fastener - Google Patents

Abstract

PURPOSE:To detect the fastening torque with high accuracy by storing the signal from a torque detector under no load into a sample-hold circuit and comparing directly with the maximum torque signal under fastening. CONSTITUTION:The fastening torque of a motor driver is detected by a torque detector 2 constituted with a stress gauge irrespective of the inertia of motor M1 as an accurate torque actually loaded to a screw. The signal from said detector 2 under no load is stored into a sample-hole circuit 44 and provided together with the direct maximum signal under fastening from the torque detector 2 to a differential amplifier 45 to feed a highly accurate fastening torque detection level where drift due to the temperature variation has been cancelled is fed to, a disply 55 through a digital decision circuit 52 and AD converter. In such a manner, highly accurate detection and display of fastening torque and decision of fastening state can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention detects the reaction force of torque when tightening a screw, uses the detected output to digitally display the torque value when tightening a screw, and also indicates whether the screw tightening condition is good or not. This invention relates to a screw tightening device that automatically determines the

Conventional configuration and its problems In conventional screw tightening devices, for example, in screw tightening devices using a DC motor, the armature current of the motor is detected.When the load increases, that is, when tightening torque increases, the current increases Taking advantage of the fact that the value increases proportionally, when a predetermined current value is reached, the power to the motor is cut off, tightening is performed to a constant torque, and the set current value is converted to a torque value and displayed digitally. there were. In such a configuration, the relationship between the electric current value of the motor and the tightening torque is statically proportional.

However, in actual screw tightening work, when the screw head seating surface sits on the tightening surface, the motor armature that is rotating at high speed is subjected to a sudden deceleration effect, so the armature current value is Torque is generated in the tightening direction regardless of and, and this torque is applied to N/, so the actual tightening torque value will be larger than the armature current value. That is, the armature current value has the disadvantage that accurate tightening cannot be converted into a digital display to a torque value.

For self-tapping screws, wood screws, etc., the final tightening torque value may be greater than the torque value at the initial 11Jj stage when the screw is tightened into the material. The sequel will explain when/when it cannot be used with a device configured to treat torque as the maximum value of torque.
There was this drawback.

Purpose of the Invention The present invention solves the above-mentioned drawbacks.Actual final tightening is performed by detecting the reaction force of torque, and using the detected output to display the torque value digitally. The purpose of the present invention is to provide a screw tightening device that determines whether the condition is good or bad.

Structure of the Invention The present invention includes a drive source, a bit that transmits tightening torque from the drive source to the screw, a torque detector that detects torque, and amplifies the signal from the torque detector. a sample-and-hold circuit that holds a signal from the previous-stage amplifier when the torque detector is in a no-load state; a reset signal circuit that takes the signal from the previous-stage amplifier into the sample-and-hold circuit for operation; A differential amplifier which receives the signal from the sample and hold circuit and amplifies the difference in g, a peak hold circuit which holds and stores the maximum value of the signal of the differential amplifier, and a signal of the differential amplifier. A measurement signal circuit that inputs the value into the peak hold circuit and operates it, a torque setting device that can set the upper and lower limit values according to the torque and outputs the set value signal, and a signal and torque setting for the peak hold circuit. A digital judgment memory circuit compares the signals of the peak hold circuit, determines whether the signal value of the peak hold circuit is within the signal value range set by the torque setting device, and outputs the signal, and converts the signal of the peak hold circuit into a digital signal. It is composed of a digital display that includes an 8-D conversion circuit, and can be tightened with high precision without malfunction by measuring the torque value, and by determining whether the condition of the screw is good or bad.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, an electric trino for screw tightening 1 is fixed to a torque detector 2, and the torque detector 2 is connected to a bracket 3.
It is fixed to the plate 4 via the upper slide block 5 and is further housed in the upper slide block 5. Air/linda 6 is bracket 7
The upper slide block 5 is fixed to the middle part of the lot 8.
It is fixed by two nuts 9-a and 9-b.

10 is a slide shaft which is slidably fitted to the upper slide block 5. Reference numeral 11 denotes a joint connecting the electric drive bar 1 and the hitch 12. 13 is a human guide, and a catcher 14 for holding supplied screws is fixed at the lower end. A bit guide bracket 15 is slidably fitted onto the slide shaft 10 and fixed to the lower slide block 16. The lower slide block 16 is still supported at the lower end of the rod 8 of the air cylinder 6 with a nut 9-'c. A screw 17 is provided in the lot 8 between the nut 9-b and the lower slide block 16, so that the lower slide block 16 is always connected to the nut 9-C.
K is biased. Reference numeral 18 denotes a bracket that supports the light shaft l-10, and is fixed to the shear 719 together with the bracket 7. 2Q is the lowering limit of the upper slide block 5. Reference numeral 21 indicates a lowering limit of the lower slide block 16.

3 is a limit switch 22, which is fixed to the bracket 7 by a switch bracket 23. The actuator 22-a of the limit 22 is in contact with the upper slide block 5, and detects the upper limit of the upper slide block 5. do.

Next, details of the torque detector 2 will be explained with reference to FIG.

Torsion detection 6 main body 24 is attached to bolt 25 on top of bracket 3
Fixed by Torque detection.

The vessel body 24 is provided with through holes 2 so that axial torsional strain is likely to occur.
6 is provided to form a hollow thin shaft portion 27. A strain gauge 728 is pasted on the outside fI']lIK of this hollow thin shaft portion 27. On top of the torque detector main body 24 (is plate 2
9 is fixed by bolt 3Q, and plate 2
At 9V'C, the holder 31 is fixed with a bolt 32. The holder 31 fixes the electric screwdriver 1 so as to be concentric with the torque detector main body 24. Reference numeral 33 denotes an output shaft of the electric screwdriver 1, which is provided in the through hole 26 and is rotatably mounted by a bearing 34.

35 is a cover, the lower part of which is fixed to the torque detector main body 24 with bolts 36, and the upper part (d bearing 37 is inserted.
It is inserted in 4. 38 (is a connector with strain gauge 2
8 signal lines are connected.

FIG. 5 is a block diagram of the entire electric circuit, and the part surrounded by broken lines is a circuit for measuring and determining screw tightening torque. FIG. 6 is a timing diagram of the screw tightening device of the present invention.

The operation of the screw tightening device configured as described above will be explained below.

When the air cylinder 6 descends while the electric screwdriver 1 is rotating, the upper slide block 5 fixed to the rod 8 also begins to descend, and the torque detector 2 attached thereto via the grate 4 and the bracket 3 and the electric Try bar 1 or descend. The lower slide block is also biased by the spring 18 to the nut 9-CK at the lower end of the rod 8, so it descends at the same time, and the hit guide bracket 15 and the bit guide 1
3. The catcher 14 also descends. The screw 39 held by the catcher 14 is tightened until it reaches the object 40, and the force of one rotation of the electric drive bar 1 is applied to the output shaft 33, the joint 11, and the bit 1.
2 to the screw 39, and is tightened by the tightening bolt 40. The rotational force of the electric screwdriver 1 is torque, and the tightening force is the torque d, which is the reaction force of the bracket 3.
The holder 31 is attached to the torque detector main body 24 which is attached to the
, is transmitted via the plate 29, and the torque detector body 2
4 is fixed by a bolt 25, which causes torsional strain in the hollow thin-walled shaft portion 27. This torsional strain is converted into a change in electrical resistance by the gauge 28 and sent to the preamplifier 41 via the connector 38. It is well known that a strain gauge is attached to the outer circumferential surface of a rotating shaft, and a torque converter that utilizes changes in the electrical resistance of such a strain gauge is widely used. Next, the operation of the electric circuit will be explained with reference to FIGS. 5 and 6.

A reference voltage is applied from the bridge power supply 42 to the input line of the torque detector 2 via the connector 38.

A minute signal voltage proportional to the screw tightening torque is output from the output line of the torque detector 2. This minute signal voltage is amplified by the preamplifier 41, and is then amplified by the low-pass filter circuit 43.
As a result, noise and high frequency vibration components generated from the electric screwdriver 1 are blocked, and the sample hold circuit 44
is input to. Sample hold circuit 44 RESET
During the ON period of the signal, the output voltage of the low filter 43 is taken in and stored as an analog value. Therefore, the torque output during the period from t1 to t2 in FIG. 6 is stored. The differential amplifier 45 receives the outputs of the low-pass filter circuit 43 and the sample-and-hold circuit 44, and amplifies the difference between these two. The output of the differential amplifier 45 is controlled by the 1° electronic switch circuit 46 which is input to the MEAS signal, and when the MEAS signal is ON, the output of the differential amplifier 45 is connected to the peak hold circuit 4γ. However, when it is OFF, it serves as a changeover switch that connects QV (Hol l-) to the peak hold circuit 47. Peak hold circuit +7 (dREsE
When the T signal is OFF, the input voltage is memorized directly from the analog output, and when the RESET signal is set to ○, the output is set to oV.

Therefore, the peak hold circuit 47 holds and stores the peak value of the torque corresponding to the maximum value of the output of the differential amplifier 45 while the MEAs signal is ON, that is, the voltage corresponding to TP in FIG. 6. The output of the peak hold circuit 47 is compared by comparators 60 and 51 with voltage values applied by a variable resistor 48 that sets the lower limit value of peak torque and a variable resistor 49 that sets the upper limit value of the peak torque. The outputs of the two comparators 50, 51 and the MEAS signal, RE
The SET signal is input to the digital judgment storage circuit 52, and if it is within the voltage level range set by the two variable resistors 48 and 49, it is an OK double signal, and if it is outside the range, it is a NG double signal at the falling edge of the MEAS signal. Output with. On the other hand, the output of the peak hold circuit 47 is also input to the A-D converter circuit 53, and is analog-to-digital converted at the falling timing of the MEAS signal. Therefore, the number display circuit 54
The numerical value displayed on the display 65 via is a value corresponding to the peak value of torque.

The electric screwdriver control circuit 56 controls the motor of the electric screwdriver 1, and also sends a RESET signal and MEAS to a circuit that measures screw tightening torque and displays judgment.
It generates a signal.

The operation will be explained in detail with reference to FIG. 5TAR, which means the start of screw tightening, from the operator or other automatic machine
When the T signal is received, a voltage corresponding to the screw tightening torque setting value is applied to the motor of the Amazu electric screwdriver to rotate it.

A RESET signal is generated under the control of a timer between timings t1 and t2 when the motor speed is stable, the motor current is constant, and the reaction torque is zero. Subsequently, after passing the timing t3 when the screw starts to penetrate into the object to be fastened, the timing t
ME similarly managed with a timer at timings 4 to t6
Generates an AS signal. While this MEAS signal is ON, the screw is seated and the screw tightening is completed. Then, the maximum torque while the MEAS signal is ON becomes the screw tightening torque, so by holding that value through the peak hold circuit 47 (C), it becomes possible to display the torque peak.

By the way, while the RESET signal is ON, the reaction torque applied to the torque detector 2 is zero. Therefore, the fifth
The output voltage of the torque detector 2 during this period is stored in the sample hold circuit 44 shown in the figure, and the RESET signal is turned OFF.
In this case, by inputting this stored voltage and the direct output voltage of the torque detector 2 to the differential amplifier 45, it is possible to cancel out the error caused by the drift caused by temperature changes in the torque detector 2. It becomes possible.

Note that 57 is a connector for connecting the above signal line.

As described above, according to this embodiment, since the sequel is detected by a torque detector using a strain gauge using torque as a reaction force, the actual load on the screw is accurately detected regardless of the inertia force of the motor, etc. Torque can be detected for proper tightening, and the sample and hold circuit stores the signal when the torque detector is in a no-load state. By inputting the 1M signal recorded in the sample hold circuit to the differential amplifier, errors due to drift caused by temperature changes in the torque detector can be canceled out, allowing for highly accurate tightening. Can detect and measure torque.゛Advantageous Effects of the Invention As mentioned above, the present invention includes a driving source, a bit that transmits torque from the driving source to the screw, a torque detector that detects tightening torque, and a torque detector that detects the torque. a preamplifier that amplifies the signal from the preamplifier, a sample hold circuit that holds the signal from the preamplifier when the torque detector is in a no-load state, and a reset signal that takes the signal from the preamplifier into the sample hold circuit and operates. a differential amplifier that receives signals from a pre-stage amplifier and a sample-and-hold circuit as input and amplifies the difference between the two signals; a beacross circuit that holds and stores the maximum value of the signal of the differential amplifier; There is a measurement signal circuit that inputs the signal from the dynamic amplifier into the peak hold circuit for operation, a torque setting device that outputs a set value signal for setting the upper and lower limits of required tightening according to the torque, and a peak hold circuit. A digital judgment memory circuit that compares the signal with that of the torque setting device, determines whether the signal value of the peak hold circuit is within the signal value range set by the torque setting device, and outputs a signal, and a peak hold circuit. By installing a digital display that includes an A-D conversion circuit that converts the signal into a digital signal, tightening is detected by a torque detector using torque as a reaction force. Torque can be detected, and the signal when the torque detector is in a no-load state is stored in the sample and hold circuit, and then the direct maximum signal from the torque detector at the time of screw tightening is stored in the sample and hold circuit. By inputting the difference between the detected signals to a differential amplifier that amplifies the difference, it is possible to cancel out the error due to drift caused by temperature changes in the torque detector. It is possible to judge whether the condition is good or bad, and its practical effect is great.

[Brief explanation of the drawing]

Fig. 1 is a side view of the main parts of a screw tightening device according to an embodiment of the present invention, Fig. 2 is a plan view of the main parts of the plate guide bracket in Fig. 1, and Fig. 4 is a cross section of the main parts of the torque detector. 5 is an electric circuit block diagram of the same embodiment, and FIG. 6 is a typing diagram of the same operation. 1...Electric screwdriver, 2...Torque detector, 24-...Torque detector body, 27...Hollow thin wall shaft, 28...Strain gauge, 41...Previous stage Amplifier, 44...Sample and hold circuit, 45...
・Differential amplifier, 47 ・Peak hold circuit, 48,
49... Variable resistor, 50.51 Comparator, 52 Digital judgment storage circuit, 55... Display, 56... Electric driver control circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 5 Figure 6

Claims (1)

[Claims] A driving source, a bit that transmits tightening torque from the driving source to the screw, a torque detector that detects the tightening torque, a preamplifier that amplifies the signal from the torque detector, and a torque detector. A sample and hold circuit that holds the signal from the preamplifier when the is in a no-load state, a reset signal circuit that takes the signal from the preamplifier into the sample and hold circuit, and inputs signals from the preamplifier and the sample and hold circuit. a differential amplifier that amplifies the difference between the two signals, a peak hold circuit that holds and stores the maximum value of the signal of the differential amplifier, and a measurement signal that takes the signal of the differential amplifier into the peak hold circuit and operates. Two limit values and a lower limit value can be set depending on the torque for the circuit and the required tightening, and the torque setting device outputs the set value signal, and the signal from the peak hold circuit is compared with the signal from the torque setting device, and the peak hold is performed. Includes a digital judgment memory circuit that determines whether the signal value of the circuit is within the signal value range set by the torque setting device and outputs the signal, and an A-D conversion circuit that converts the signal of the peak hold circuit into a digital signal. A screw tightening device equipped with a digital display.