JPH0238353B2 - NEJISHIMESOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a screw tightening device that detects reaction torque when tightening a screw, controls the screw tightening torque based on the detected output, and determines whether the tightening condition is good or bad. It is.

Conventional structure and problems In conventional screw tightening devices that use a DC motor, the screw tightening torque varies widely due to the influence of inertia torque generated in rotating parts such as the DC motor and the bit of the screwdriver. There is a problem, and as a means to solve this problem, a screw tightening device that controls the voltage applied to the DC motor by switching it in two stages is known. In this method, the current value of the DC motor is detected as a means of detecting the screw tightening torque, so there is a problem that the tightening accuracy is not good, and that the final tightening torque value When the torque value is large at the initial stage when the material is embedded into the tightening material, the first
There was a problem in that the voltage applied to the DC motor in the first stage could not be used because it had to be lower than the voltage applied in the second stage. Furthermore, for the same reason, the DC motor cannot be rotated at a high speed until the screws are seated, so there is a drawback that the time required to tighten the screws becomes longer.

On the other hand, Japanese Patent Laid-Open No. 54-127099 is known as an improved two-step screw tightening method using a torque sensor, but errors occur due to temperature drift of the torque sensor. Another drawback was that the time required to tighten the screws was longer because the motor rotational speed was lowered during startup.

OBJECT OF THE INVENTION The present invention solves the above-mentioned conventional problems.The present invention detects the reaction force of the actual screw tightening torque with a torque detector, monitors the detected output with a microcomputer, and detects the reaction force of the actual screw tightening torque. The present invention provides a screw tightening device that controls screw tightening torque by controlling applied voltage.

Composition of the Invention The present invention fixes a torque detector to an electric screwdriver using a DC motor so that it can detect the reaction torque when tightening a screw, amplifies the output of the torque detector with an amplifier, and then converts the torque detector into an analog-to-digital converter. converts it into a digital signal and sends it to the first storage circuit and the first
The first memory circuit performs a memory operation at the timing when the reaction force applied to the torque detector is zero, and the output of the first memory circuit is also input to the first subtraction circuit. Then, the difference between the real-time output of the torque detector and the time when the reaction force is zero becomes the output of the first subtraction circuit, and the output of the first subtraction circuit and the target value of the tightening torque are set. The value of the first digital setting switch is input to the torque control circuit, and the torque control circuit monitors the output of the torque detector at fixed time intervals and updates the maximum value in the second memory circuit. The torque control circuit calculates the difference between the ever-changing output of the torque detector and the maximum value, and if the difference is positive, the torque control circuit calculates the output voltage of the programmable DC power supply that can freely vary the voltage applied to the motor. When the output of the subtraction circuit and the value of the digital switch match, the output of the programmable DC power supply is zeroed to stop the motor, and the means for receiving a screw tightening start signal from the outside and immediately before the screw is seated is provided. The output of the amplifier is connected to a peak hold circuit, the output is converted to a digital value by an analog-to-digital converter, and this value and the memory circuit are connected to a peak hold circuit. Find the output difference in the second subtraction circuit, display the result numerically, and
Second and third setting switches are provided for setting upper and lower limits of the screw tightening torque, and these set values are compared with the output of the second subtraction circuit to determine whether the screw tightening torque is good or bad. It is a screw tightening device.

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

FIG. 1 shows a side view of the mechanical part of the screw tightening device.

In FIG. 1, an electric screwdriver 1 for tightening screws is fixed to a torque detector 2, and the torque detector 2 is fixed to a plate 4 via a bracket 3, and further attached to an upper slide block 5. The air cylinder 6 is fixed to a bracket 7, and the upper slide block 5 is attached to the middle part of the rod 8 with two nuts 9.
-a and 9-b. Reference numeral 10 denotes a slide shaft into which the upper slide block 5 is slidably fitted. 11 is a joint connecting the electric screwdriver 1 and the bit 12. Reference numeral 13 denotes a bit guide, and a catch 14 for holding supplied screws is fixed at the lower end. A bit guide bracket 15 is fixed to a lower slide block 16 which is slidably fitted to the slide shaft 10. Further, the lower slide block 16 is supported at the lower end of the rod 8 of the air cylinder 6 by a nut 9-c. A spring 17 is provided on the rod 8 between the nut 9-b and the lower slide block 16, so that the lower slide block 16 is always held in place by the nut 9-b.
It is biased towards c. 18 is slide shaft 10
This is a bracket that supports the bracket 7, and is fixed to the chassis 19 together with the bracket 7. 20 is a lowering limit stopper of the upper slide block 5. 21 is a lowering limit stopper of the lower slide block 16.

FIG. 2 is a front view of the mechanism section with the electric screwdriver portion of FIG. 1 removed, and shows the state in which the limit switch 22 is attached. The limit switch 22 is fixed to the bracket 7 by a switch bracket 23, and its position can be adjusted up and down. The structure is such that when the upper slide block 5 descends to a predetermined position, the limit switch 22 is turned on. Adjust the position of this limit switch so that it turns on just before the screw is seated.

Next, details of the torque detector 2 will be explained with reference to FIG. Torque detector body 2 on top of bracket 3
4 is fixed with bolts 25. The torque detector main body 24 is provided with a through hole 26 to form a hollow thin shaft portion 27 so that axial torsional strain is likely to occur. A strain gauge 28 is attached to the outside of this hollow thin shaft portion 27. A plate 29 is fixed onto the torque detector main body 24 with bolts 30, and a holder 31 is further fixed to the plate 29 with bolts 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. 3
5 is a cover, the lower part of which is the torque detector main body 24
A bearing 37 is inserted into the upper part. Further, the inner ring of the bearing 37 is inserted into the torque detector main body 24. 38 is a connector to which a signal line 39 of the strain gauge 28 is connected.

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 and the electric Driver 1 descends. Further, since the lower slide block is also urged by the spring 18 to the nut 9-c at the lower end of the rod 8, it descends at the same time, and the bit guide bracket 15, bit guide 13, and catcher 14 also descend. Catcher 1
4 reaches the fastener 41, the rotational force of the electric screwdriver 1 is transmitted to the screw 40 via the output shaft 33, the joint 11, and the bit 12, and the screw 40 is tightened by the fastener 41. The rotational force of the electric screwdriver 1 is a tightening torque, and the tightening torque is used as a reaction force to apply a bolt 31 to the torque detector body 24 attached to the bracket 3.
The torque is transmitted through the plate 29, and since the lower part of the torque detector main body 24 is fixed by a bolt 25, a torsional strain is generated in the hollow thin 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. A torque transducer in which a strain gauge is attached to the outer circumferential surface of a rotating shaft, and which utilizes changes in the electrical resistance of such a strain gauge, is widely used as a well-known fact.

Next, the configuration of the control circuit of the embodiment will be explained with reference to FIG.

Bridge power supply 42 is connected to the input line of torque detector 2.
A reference voltage is applied via 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 a preamplifier 43, and a low-pass filter circuit 44 blocks noise and high frequency vibration components generated from the motor 1 of the electric screwdriver, and inputs it to a peak hold circuit 45. The peak hold circuit 45 receives the RS signal.
When it is OFF, the peak of the input voltage is stored as an analog value, and when the RS signal is ON, the output is 0V. The voltage switch 46 is a switch circuit that selects one of the two analog signal inputs using the S1 signal and outputs the same voltage. When the S1 signal is OFF, the output of the low-pass filter circuit 44 is selected. When the S1 signal is ON, the output of the peak hold circuit 45 is selected. 4
8 is a microcomputer (hereinafter abbreviated as microcomputer) which has a ROM (read only memory), a RAM (random access memory), and an input/output interface circuit, and is equipped with an arithmetic function.

The signal selected by the electronic switch 46 is input to an analog-to-digital conversion circuit 47 (hereinafter abbreviated as an A-D conversion circuit), converted into a digital signal, and input to the microcomputer.

Therefore, the microcomputer can control the control signal S1 of the electronic switch and switch between the torque peak value v _p and the ever-changing torque value. Further, the start of A-D conversion is performed at the timing of the rise of the ADST signal from the microcomputer 48,
When the A-D conversion is completed, an ADEND signal is output.

On the other hand, 49 is a programmable DC power supply that can vary the effective value of DC voltage output, and is used to vary the voltage V _M applied to the motor 1 of the electric screwdriver. The number display circuit 50 is connected to the microcomputer 4
8 and digitally displays the peak torque value. The setting switch 51 is used by the operator to set the target value, upper limit value, lower limit value, etc. of the screw tightening torque as digital values. The air cylinder 6 is controlled by a microcomputer 48 via a relay 52. Also, as a control signal from the outside via the connector 38c.
START, STOP, and MEAS are input to the microcomputer 48. In addition, 38, 38a, 38b, 38c
indicates a connector.

Next, the operation of the present invention will be explained in detail with reference to FIG. When the power is turned on, the microcomputer 48 switches the electronic switch ₄₆ to output the torque output v0, which is the output of the low-pass filter circuit 44, and outputs A-D.
Input via converter 47. START, which signals the start of screw tightening from a worker or other automatic machine
Upon receiving the signal, the microcomputer 48 first stores the torque output v ₀ . The stored value of the torque output v ₀ is the value when the reaction torque received by the torque detector 2 is zero since the screw tightening operation has not started.

Next, the air cylinder 6 is turned on, the programmable DC power supply 49 is set to the rated voltage _VR , and the motor of the electric driver 1 is rotated at high speed.
The control signal S1 of the electronic switch 46 is turned OFF, and the real time value of the torque detector 24 is set to the A-D converter 47.
Allow input via . Also, as a result of tightening the number display circuit 50 and the screw, the judgment result is OK/NG whether the peak torque is between the upper and lower limits of torque set by the setting switch.
Also reset the signal.

The motor rotates, and at timing _t1 , its speed stabilizes and the motor current becomes constant. Next, after timing t ₂ when the screw starts to sink into the object to be fastened, the limit switch 22 activates the limit switch indicating that the screw is about to be seated.
MEAS signal is output at timing _t3 . Then, the microcomputer 48 makes the output V _M of the programmable DC power supply 49 zero, short-circuits both terminals of the motor, and quickly stops the motor. The screws are still tightened during this time. At time _t4 , which is a certain period of time _T1 after timing _t3 , a reset signal _Rs is output to set the output of the peak hold circuit 45 to 0V. On the other hand, the output voltage V _M of the programmable DC power supply is set to a voltage V _s that is approximately 1/2 to 1/4 of the voltage required to generate the target screw tightening torque. The motor then tightens the screw at a low rotation speed. Eventually, timing t ₅
At this point, the screw is seated and the torque output v increases rapidly. The microcomputer 48 is an A-D conversion circuit 47
On the other hand, A-D in a short period from timing _t5
A conversion start signal ADST is given, and this torque output v is constantly monitored. At time _t6 when this torque output v exceeds a value _vt of about 1/2 to 1/4 of the set tightening torque, the microcomputer 48 changes the output V _M of the programmable DC power supply 49 at fixed time intervals (ΔT). Increase linearly. Since it is already seated, the screws are gradually tightened at low speed. The microcomputer 48 monitors the output of the A/D conversion circuit 47 until the torque output reaches a predetermined tightening torque value v _p . However, when the same voltage is applied to the motor and the screws are tightened at timings t ₇ - _{t 8} and t ₉ - t ₁₀ in Figure 5, the torque required to tighten the screws suddenly decreases.
It may then increase again. The cause is
This is thought to be because, after the screw is seated, the frictional force at the interface between the base material to be screwed and the screw head changes as the screw rotates. in this case,
Microcomputer 48 outputs programmable DC 49
The linear increase in V _M over time is temporarily stopped and the voltage is kept at a constant voltage (at times t ₇ and t ₉ ). Then, the maximum value of the torque output v up to now, that is, the value of v ₁ at timing t ₇ and the value of v ₂ at timing t ₉ is stored. Thereafter, the value of the torque output v is continued to be monitored, and from timing t ₈ or t ₁₀ when the torque output v exceeds the stored maximum value v ₁ or v ₂ , the output of the programmable DC power supply 49 is changed in time again. increase proportionately. Then the torque output v
At timing _t11 when the value of V a reaches the target tightening torque v _a , the microcomputer 48 makes the output V _M of the programmable DC power supply 49 zero and stops applying voltage to the motor.

After some waiting time from the time _t11 , the microcomputer 48 turns on the _S1 signal at timing _t12 , and the A-D
The input side of the conversion circuit 47 is changed to the peak hold circuit 45 by the electronic switch 46, and after waiting for some time again, the peak value v _p of the torque output is inputted at timing _t13 . The microcomputer 48 outputs the difference between v _p and the v _p , that is, the value (v _p −v _p ), to the number display circuit 50 as a peak torque value. Furthermore, this (v _p −v _p )
The value of is determined and an OK/NG signal is also output. As already mentioned, the value of v _p is the value when the reaction torque applied to the torque detector 2 is zero. Therefore, (v _p
-v _p ), it is possible to cancel out errors due to drift caused by temperature changes in the torque detector 2 and the preamplifier 43. timing
From t ₁₃ onwards, the microcomputer 48 is in the same state as immediately after the power is turned on, switches the electronic switch 46 again, that is, turns off the S1 signal, reads the torque output v via the A-D converter 47, and then outputs the next START signal again. Wait for it to turn on.

By the way, since the rated voltage is applied to the motor from the time of starting until just before seating, it is possible to fasten the screws at high speed, and the screws can be tightened without any problem even if the torque is large when the screws penetrate into the tightening material.

In addition, since the motor is rotated at high speed until just before the screw is seated, the time required for the screw to sink into the material can be shortened.

Then, the motor is stopped just before the screws are seated, and then the microcomputer controls the programmable DC power supply to tighten the screws at low speed. When the target tightening torque is reached, the voltage applied to the motor is reduced to zero. . Since screw tightening is completed at low speed, the influence of motor inertia is eliminated, allowing accurate screw tightening with less variation in screw tightening torque.

FIG. 6 shows a schematic flowchart of the microcomputer for operating as described above. Note that the timing t ₃ was detected by the external MEAS signal, but the microcomputer 48 uses a timer to detect the timing from t ₀ .
Similar control is possible by managing the time up to _t3 . In addition, two A-D converters are installed,
It is also possible to adopt a configuration in which the outputs of the peak hold circuit 45 and the low-pass filter circuit 44 are independently A/D converted, and to eliminate the electronic switch 46.

Effects of the Invention According to the present invention, first, the screw tightening torque is measured as a reaction force by a torque detector fixed to an electric screwdriver, and at the timing when the reaction force of the torque detector is zero, the signal output of the torque detector is set to A. -D conversion is performed and stored in the microcomputer, and the measurement accuracy of screw tightening torque can be improved by using the value of the difference between the signal output of the torque detector and this memorized value as the screw tightening torque during screw tightening control. . Next, the programmable power supply is controlled by a microcomputer, and the rated voltage is applied to the motor of the electric screwdriver until just before the screw is seated.The motor is stopped quickly just before the screw is seated, and then the voltage applied to the motor is gradually increased. monitor the screw tightening torque, and if the screw tightening torque value tends to decrease, fix the voltage applied to the motor, and only apply voltage to the motor when the screw tightening torque value increases from the previous maximum value. Tighten slowly by increasing the voltage, monitor the signal output of the torque detector with a microcomputer, and stop the motor of the electric screwdriver when this signal output reaches a preset tightening torque. By performing such control, it has become possible to shorten the screw tightening time, reduce variations in the tightening torque, and perform highly accurate screw tightening.

Furthermore, the peak torque of screw tightening was stored as an analog value in a peak hold circuit, the difference between the A-D converted value and the value when the reaction force of the torque detector was zero was determined, and the difference was set with a setting switch. By making it possible to compare the upper and lower limits of the screw tightening torque, it is now possible to accurately judge the screw tightening results.

[Brief explanation of drawings]

Fig. 1 is a side view of the mechanism of a screw tightening device according to an embodiment of the present invention, Fig. 2 is a front view of the mechanism with the electric screwdriver part removed from Fig. 1, and Fig. 3 is the mechanism of the torque detector. 4 is a control circuit block diagram of the same embodiment, FIG. 5 is an operation timing chart of the same, and FIGS. 6a and 6b are flowcharts of the same microcomputer. 1... Electric screwdriver, 2... Torque detector, 2
2...Limit switch, 24...Torque detector main body, 27...Hollow thin wall shaft portion, 28...Strain gauge, 42...Bridge power supply, 43...Pre-stage amplifier, 45...Peak hold circuit, 47...A −
D conversion circuit, 48...Microcomputer, 4
9...Programmable DC power supply, 50...Number display circuit, 51...Setting switch.

Claims (1)

[Claims] 1. A DC motor, a bit that transmits the tightening torque from the DC motor to the screw, a torque detector that detects the tightening torque as a reaction force, an amplifier that amplifies the signal of the torque detector, and an amplifier. an analog-to-digital converter for converting the output of the torque detector into a digital value; a first storage means for storing the output of the analog-to-digital converter when the reaction torque received by the torque detector is zero; and a screw tightening torque. a first setting switch for setting a target value of digitally, a programmable DC power supply that can vary the DC voltage output by a digital input signal, and A first subtraction circuit that calculates a difference from a value stored in the storage means, a pre-seating detection means that detects a timing immediately before the screw is seated, and a target value of the first setting switch is compared with the first subtraction circuit and the first setting switch. and a first comparison circuit that outputs a coincidence signal and receives a screw tightening start signal from an external device, and applies the output of the programmable DC power supply to the rated voltage of the DC motor until the output of the pre-seating detection means is received. receiving the output of the first torque control circuit and the pre-seating detection means, and setting the output of the programmable DC power supply to a value that causes the DC motor to generate a torque that is a fraction of the screw tightening target torque. seating detection means for monitoring the output of the first subtraction circuit to detect the timing at which the screw is seated; a second subtraction circuit that calculates the difference between the signal of the torque detector and the second storage means; a second subtraction circuit that receives the output of the seating detection means; A screw tightening device comprising a second torque control circuit whose output is positive and which gradually increases the output of the programmable DC power supply until a match signal is output from the first comparison circuit. 2. A DC motor, a bit that transmits the tightening torque from the DC motor to the screw, a torque detector that detects the tightening torque as a reaction force, an amplifier that amplifies the torque detector signal, and converts the output of the amplifier into a digital value. The analog/digital converter and the torque detector receive the analog/digital converter when the reaction torque is zero.
A first storage means for storing the output of the digital converter, a first setting switch for setting the target value of the screw tightening torque as a digital value, and a programmable DC power supply that can vary the DC voltage output by a digital input signal. a first subtraction circuit that calculates the difference between the output of the analog-to-digital converter and the value stored in the first storage means during screw tightening; and a pre-seating detection means that detects the timing immediately before the screw is seated. and a target value of the first subtraction circuit and the first setting switch, and outputs a matching signal.
and a first torque control circuit that receives a screw tightening start signal from an external device and applies the output of the programmable DC power supply to the rated voltage of the DC motor until receiving the output of the pre-seating detection means. , receiving the output of the pre-seating detection means, setting the output of the programmable DC power supply to a value for the DC motor to generate a torque that is a fraction of the screw tightening target torque, and the first subtraction circuit; seating detection means for detecting the timing at which the screw is seated by monitoring the output of the seating detection means, and a second storage means for receiving the output of the seating detection means and updating and storing it every time there is a maximum value of the signal from the torque detector thereafter. and a second subtraction circuit that calculates the difference between the signal of the torque detector and the second storage means, and receives the output of the seating detection means, and the output of the second subtraction circuit is positive, and a second torque control circuit that gradually increases the output of the programmable DC power supply until a match signal is output from the first comparison circuit; and a peak hold circuit that converts the maximum value of the output of the amplifier into a digital value and stores it. a reset circuit that receives the output of the pre-seating detection means and generates a reset signal for the peak hold circuit; and a third subtraction circuit that calculates the difference between the output of the peak hold circuit and the storage means;
a number display circuit that displays the output of the third subtraction circuit;
The output of the third subtractor is compared with the second and third setting switches for setting the upper and lower limits of the screw tightening torque using digital values, and A screw tightening device equipped with a second comparison circuit that determines whether the tightening torque is good or bad.