JPS6090677A - Clamping device for screw - 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 Field of Industrial Application The present invention detects the reaction torque during screw tightening, controls the screw tightening torque based on the detected output, and determines whether the tightening condition is good or bad. This invention relates to a tightening device.

Conventional configuration and its problems Conventional screw tightening devices that use a DC motor,
There is a problem in that there is a large variation in torque when tightening screws due to the influence of inertia l and torque generated in rotating parts such as the DC motor and the focus of the screwdriver.As a means to solve this problem, the No. 120986 discloses a screw tightening device that controls the voltage applied to a DC motor by switching it to two levels. With 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. When the torque value is large at the initial stage when the screw is tightened into the material, the voltage applied to the DC motor in the first stage is
There was a problem in that it could not be used unless the applied voltage was lower than that of the step. For the same reason, the DC motor cannot be rotated at a high speed at the screw where the screw is seated, so it takes a long time to tighten the screw.

Purpose of the Invention The present invention eliminates the above-mentioned conventional problems.
A screw tightening device that detects the reaction force of the actual screw tightening torque with a torque detector, monitors the detection output with a microcomputer, and controls the applied voltage of a DC motor to control the screw tightening torque. It also has functions to display the final torque of screw tightening and to judge pass/fail.

Structure of the Invention The present invention has a torque detector fixed to an electric screwdriver using a DC motor so as to be able to detect the reaction torque when tightening a screw, and after amplifying the output of the torque detector with an amplifier, analog It is converted into a digital signal by a digital converter and inputted to a storage circuit and a first subtraction circuit, and the storage circuit performs a storage operation at the timing when the reaction force applied to the torque detector is zero, and the storage circuit outputs the signal. is also input to the subtraction circuit so that 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 subtraction circuit, and the output of the first subtraction circuit and the target tightening torque are The value of the first digital setting switch for setting the value is input to the torque control circuit, and the torque control circuit changes the output voltage of the programmable DC power supply that can freely vary the voltage applied to the motor from the timing immediately before the screw is applied. means for controlling and gradually increasing the output, and when the output of the subtraction circuit and the value of the digital switch match, the output of the programmable DC power supply is made zero to stop the motor;
It has means to apply the rated voltage to the motor until the timing immediately before the screw is directly applied when receiving a screw tightening start signal from the outside, and further connects the output of the amplifier to a peak hold circuit, and converts the output from analog to digital. convert it into a digital value using a second subtraction circuit, calculate the difference between this value and the output of the storage circuit using a second subtraction circuit, display the result numerically, and
The second step is to set the upper and lower limits of screw tightening torque. This screw tightening device is provided with a third setting switch and is configured to compare these set values with the output of the second subtraction circuit to determine whether the screw tightening torque is good or bad.

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 the bracket 7, and the upper slide block 5 is attached to the middle part of the rod 8.
It is fixed by two nuts 9-a and 9-b. 10
is a slide shaft into which an upper slide block 5 is slidably fitted. 11 is electric screwdriver 1 and bit 1
It is a joint that follows 2. Reference numeral 13 denotes a pit guide, and a catcher 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 1o. In addition, the lower slide block 16 is attached to the lower end of the rod 8 of the air cylinder 6 with a nut 9-.
It is supported by C. A spring 17 is provided on the rod 8 between the nut 9-b and the lower slide block 160, and constantly biases the lower slide block 16 against the nut 9-C. A bracket 18 supports the slide shaft 1°, and is fixed to the shear 19 together with the bracket 7.

20 is a lowering limit stopper for 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 a portion of the electric screwdriver shown in FIG. 1 removed, and shows how 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 unidirectionally. The structure is such that when the upper slide block 5 descends and reaches 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.

The torque detector main body 24 is attached to the bolt 26 on the bracket 3.
Fixed by 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. Torque detector body 2
A plate 29 is fixed onto the plate 4 by bolts 3o, and a holder 31 is further fixed to the plate 29 by bolts 32. The holder 31 is the torque detector main body 2
The electric screwdriver 1 is fixed so as to be concentric with the screwdriver 4. 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 of which a bearing 37 is inserted. 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 via the plate 4 and the placket 3, and the electric Driver 1 descends. Since the bent lower slide block is also urged by the spring 18 to the naso 9-c at the lower end of the rod 8, it descends at the same time, and the bit guide bracket 1-15, bit guide 13, and catcher 14 also descend. The screw 40 held by the catcher 14 reaches the object 41 when tightened, and the rotational force of the electric screwdriver 10 is applied to the output shaft 33, the joint 11, and the bit 1.
The rotational force of the electric screwdriver 1 is transmitted to the screw 39 through the screw 2, and the torque is transmitted to the object 41.
The holder 31 is attached to the torque detector main body 24 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 stain 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 transducer that utilizes changes in the electrical resistance of such a strain gauge is widely used.

Next, the configuration of the control circuit of the embodiment will be explained with reference to FIG. The part surrounded by the broken line shows a sketch diagram of the control device of the present invention.

A reference voltage is applied from a bridge power supply 42 to the input line of the torque detector 2 via a 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 is input to a peak hold circuit 45 after noise and high frequency vibration components generated from the motor 1 of the electric driver are blocked by a low-pass filter circuit 44. The peak hold circuit 45 stores the peak of the input voltage as an analog value when the R3 signal is OFF, and outputs ○V when the R3 signal is ON. The electronic switch 46 is a switch circuit that selects one of the two analog signal inputs based on 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, and the S
When the 1 signal is ON, the output of the peak hold circuit 45 is selected. 48 is ROM (read only memory), RAM
(random access memory), input/output interface circuit, and a microcomputer (
(hereinafter abbreviated as microcomputer).

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

Therefore, the microcomputer outputs the control signal S1 of the electronic switch.
It is possible to control and take in the torque value, which changes moment by moment, such that the peak torque value is . Further, the start of A-D conversion is performed at the timing of the rise of the ADST signal from the microcomputer 48, and when the A-D conversion is completed, the ADE
An ND 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 VM applied to the motor 1 of the electric screwdriver. The numerical display circuit 50 is controlled by a microcomputer and digitally displays the peak value of torque. Setting switch 5
1 is for 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 connected to the relay 5 by the microcomputer 48.
2. Also, via the connector 38c,
5TART as an external control signal.

5TOP and MEAS are input to the microcomputer 48.

Note that 38.38a, 38b, and 38c indicate connectors.

Next, the operation of the present invention will be explained in detail with reference to FIG. When receiving the 5TART signal from the operator or other automatic machine to signal the start of screw tightening, the microcomputer 4
8 turns on the air cylinder 6, sets the programmable [100 current power supply 49] to the rated voltage vR, and rotates the motor of the electric driver 1 at high speed. electronic switch 46
The control signal S1 is turned OFF so that the real-time value of the torque detector 24 can be inputted via the AD converter 47. As a result of the number display circuit 50 and the tightening of the screws, the judgment result is ○/NG whether the peak torque is between the upper and lower limits of torque set by the setting switch.
The signal is also reset. The microcomputer 48 manages an arbitrary timing t2 between timing t4 and t3 when the motor rotates, its speed becomes stable, the motor current becomes constant, and the reaction torque becomes zero, using the timer T1. Torque output v, which is the output of the low-pass filter circuit 44 when the torque is
Store 0. Subsequently, after timing t3 when the screw starts to sink into the object to be fastened, the limit switch 22 outputs a MEAS signal of the limit switch at timing t4, which indicates that the screw is about to be seated. Then, the microcomputer 48 makes the output vM 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 t5, which is a fixed time interval after timing t4, a reset signal R8 is output, and the output of the peak hold circuit 46 is set to O■. On the other hand, the output voltage vM of the programmable DC power supply is set to a voltage Vs that is approximately % of the voltage required to generate the target screw tightening torque. The motor then tightens the screw at a low rotation speed. Eventually, at timing 70, the screw is seated and the torque output V increases rapidly.

The microcomputer 48 sends an A-D conversion start signal ADST to the A-D conversion circuit 47 in short cycles from timing t5.
is given, and this torque output V is constantly monitored. At time t6 when this torque output V exceeds a value v1 of approximately % of the set tightening torque, the microcomputer 48 linearly increases the output M of the programmable DC power supply 49 at fixed time intervals (ΔT). Since it is already seated, the screws are gradually tightened. The microcomputer 48 continues to monitor the output of the A-D converter circuit 47 until the torque output reaches a predetermined tightening torque value, and at timing t7 when the target tightening torque Va has been reached, the microcomputer 48 changes the output vM of the programmable DC power supply. At the same time, the voltage application to the motor is stopped.

After some waiting time from t7, timing t
8, the microcomputer 48 turns on Sl, and the A-D conversion circuit 4
The input side of 7 is changed to the peak hold circuit 45 by the electronic switch 46, and after waiting for some time again, the peak value of the torque output is inputted at timing t9. The microcomputer 48 outputs the difference between Vp and v0, that is, the value (vp-v), to the number display circuit 50 as a peak torque value. Furthermore, the value of this (vpVo) is determined and a /NG signal is also outputted. As already mentioned, the value of V is the value when the warping torque applied to the torque detector 2 is zero. Therefore, (
vp-vo), it is possible to cancel out errors due to drift caused by temperature changes in the torque detector 2 and the front-stage amplifier 43. On the other hand, since the rated voltage is applied to the motor from the time of start until just before seating, it is possible to tighten screws at high speed, and the screws can be tightened without any problem even if the torque is large when digging into the material. .

Then, the motor is stopped just before the screw is tightened, and then the microcomputer controls the programmable DC power supply to gradually increase the voltage applied to the motor, thereby tightening the screw at a low speed. As a result, the influence of the inertia of the motor is eliminated, and accurate screw tightening with less variation in screw tightening torque becomes possible. Since the motor is rotated at high speed just before the screw is seated, the time required for the screw to sink into the material can be shortened.

FIG. 6 shows a schematic flowchart of the microcomputer that operates as described above. Incidentally, the timing t4 was detected by an external MEAS signal, but the microcomputer 48: t was detected by the retimer.

Similar control is possible for managing the time from t4 to t4. It is also possible to eliminate the electronic switch 46 by providing two analog-to-digital converters and converting the outputs of the peak hold circuit 45 and the low-pass filter circuit 44 independently.

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 changed to A. -D converted and stored in the microcomputer,
During screw tightening control, the measurement accuracy of the screw tightening torque can be improved by using the difference between the signal output of the torque detector and this stored value as the screw tightening torque. Next, the programmable power supply is controlled by a microcomputer, and the rated voltage is applied to the motor of the electric screwdriver 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 reduced. While raising the screwdriver, slowly tighten it while monitoring the signal output of the torque detector with a microcomputer, and when this signal output reaches a preset tightening torque, control is performed to stop the motor of the electric screwdriver. As a result, the screw tightening time can be shortened, and there is less variation in tightening torque, allowing highly accurate screw tightening.

Furthermore, the peak torque of screw tightening was memorized as an analog value using a peak bold 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 using 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 the drawing]

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 a part of the electric screwdriver removed from Fig. 1, and Fig. 3 is the mechanism of the torque detector. FIG. 4 is a control circuit block diagram of the same embodiment.
Figure 5 is a timing diagram of the same operation, Figure 6 (-), (b
) is a flowchart diagram of the same microcomputer. 1...Electric screwdriver, 2...Torque detector, 22...Rimisoto switch, 24...
・Torque detector body, 2A...Hollow thin-walled shaft part, 2
8...Strain gauge, 42...Bridge power supply, 4
3...Pre-stage amplifier, Stone...Peak hold circuit, 47...A-D conversion circuit, 48...Microcomputer, 49...Programmable DC power supply, 5o... ...Number display circuit, 51...Setting switch. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 (OJ) Figure 6 th+

Claims (2)

[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 torque detector signal, and a digital output of the amplifier. an analog-to-digital converter for converting into a value, a 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 target value for the screw tightening torque as a digital value. A first setting switch for setting, a programmable DC power supply whose DC voltage output can be varied by a digital input signal, and calculating the difference between the output of the analog-to-digital converter and the value stored in the storage means during screw tightening. a first subtraction circuit for detecting a timing immediately before the screw is seated; and a first subtraction circuit for comparing a target value of the first setting switch with a target value of the first setting switch and outputting a matching signal. a first torque control circuit that receives a screw tightening start signal from a comparison circuit and 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; In response to the output of the pre-seating detection means, the output of the programmable DC power supply is set to a value that the DC motor should generate, which is a fraction of the screw tightening target torque, and the output of the first subtraction circuit is set. direct detection means for detecting the timing of seating of the screw by monitoring the timing of the screw seating; and a second direct detection means for receiving the output of the direct detection means and gradually increasing the output of the programmable DC power supply until a match signal is output from the first comparison circuit. Screw tightening device with torque control 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 a digital output of the amplifier. an analog-to-digital converter for converting into a value, a 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 target value for the screw tightening torque is set as a digital value. A first setting switch of the terminal, a programmable DC power supply whose DC voltage output can be varied by a digital input signal, and dividing the difference between the output of the analog-to-digital converter and the value stored in the storage means during screw tightening. a first subtraction circuit for detecting a timing immediately before the screw is seated; and a first subtraction circuit for comparing a target value of the first setting switch with a target value of the first setting switch and outputting a matching signal. a comparison circuit; 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; In response to the output of the pre-seating detection means, the output of the programmable DC power supply is set to a value at which the DC motor should generate a torque that is a fraction of the screw tightening target torque, and the output of the first subtraction circuit is direct detection means for monitoring the output and detecting the timing when the screw is seated; and a second direct detection means for receiving the output of the direct detection means and gradually increasing the output of the programmable DC power supply until a match signal is output from the first comparison circuit. The torque control circuit includes: 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; a second subtraction circuit that calculates the difference between the output of the hold circuit and the storage means; a number display circuit that displays the output of the second subtraction circuit; and digital values for setting upper and lower limits of screw tightening torque. the output of the second and third setting switches, the output of the second subtracter, and the second. A screw tightening device comprising a second comparison circuit that compares the torque with a third setting switch and determines whether the screw tightening torque is good or bad.