JPH0696210B2 - Automatic screw tightener - Google Patents

Description

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

[Prior Art] Recently, when assembling parts, strict control of tightening torque is required, and automatic screw tightening equipped with a torque detection mechanism that detects the torque during tightening and stops the motor if this reaches a predetermined tightening torque value. A lot of machines are used. The torque detection mechanism of this kind of automatic screw tightening machine is equipped with a strainer for detecting a reaction force applied to the driver bit at the time of tightening and a detection resistor composed of four strain gauges attached to this strain tube and constituting a bridge circuit, The reference voltage is supplied from the input end of the bridge circuit, and the amount of strain of the strain tube is detected as the amount of electricity from the output end of the bridge circuit. With an automatic screw tightener equipped with this torque detection mechanism, the correction unit selects the amplification factor for zero correction and gain correction based on the value obtained by using a weight before starting the tightening work, and Static calibration is performed so that the amount of electricity detected at the output end is amplified by this amplification factor to obtain a theoretical torque value according to the actual amount of distortion. After this static calibration, this automatic screw tightener starts screw tightening, and when the completion of tightening is detected, the amount of strain received by the strain tube due to the reaction force of the driver bit is detected as tightening torque and displayed on the display. It is displayed. However, in the case of an ordinary screw tightener, the reaction force of the driver bit is transmitted to the strain pipe through a connecting mechanism such as a universal joint, so that the mechanical efficiency thereof, the variation in the degree of fitting between the driver bit and the screw, Or, it is not transmitted to the 100% strain pipe due to the material of the work. Therefore, the measured value obtained by the worker measuring the tightened screw with a torque wrench or the like may not match the displayed value displayed on the display unit. In order to match these values, some work pieces are actually tightened at the work site, and the correction unit is adjusted so that the displayed value and the measurement value measured with the torque wrench match, and the amplification factor of the amplification unit is adjusted. Has been changed according to the type of. With this change, the output signal of the torque detection mechanism will not be obtained again based on the amplification factor of the amplification section obtained by static calibration, and static calibration will be required whenever this is necessary, which is a troublesome task. There are drawbacks such as the necessity. In addition, when it is necessary to determine abnormality such as malfunction of the strain gauge, disconnection, malfunction of the amplifier, etc.,
The reference value to be compared in the judgment is obtained from the relationship between the distortion amount of the distortion tube and the torque based on the amplification factor of the amplification section obtained by static calibration. Even if the output signal of the torque detection mechanism obtained by changing the above is compared, it is not possible to accurately determine the abnormality, and it is meaningless to perform these comparisons.

The present invention is intended to eliminate the above-mentioned drawbacks, and even if the display value is changed so that the display value and the measurement value actually measured by the torque wrench match, the amplification unit obtained by the static calibration. It is an object of the present invention to provide an automatic screw tightening machine equipped with a torque detection mechanism that can obtain an output signal based on the amplification factor of.

[Means for Solving the Problems] In order to achieve the above-mentioned object, a driver base that is raised and lowered by an elevation drive source holds a rotatable driver bit in response to rotation of a motor. A strain tube for detecting a reaction force applied to the driver bit and four detection resistors which are attached to the strain tube and constitute a bridge circuit are attached to the driver base. A voltage supply source that supplies a reference voltage is connected to the input end of the bridge circuit, and the strain amount of the strain tube is detected from the output end of the bridge circuit as an electric amount, and this is selected as an arbitrary amplification factor. It is configured to be sent to the first amplification unit having one correction unit. The first
The output signal of the amplification section is branched into two directions, one of which is directly sent to the switching section, and the other is sent to the switching section through a second amplification section having a second correction section for selecting an arbitrary amplification factor. Is configured. The switching unit is configured to be driven by a control unit that supplies either the output signal of the first amplification unit or the output signal of the second amplification unit to the display unit by its operation.

Further, instead of branching the output signal of the first amplifying section in two directions, this output signal is sent to an AD converting section to be converted into a digital amount, while a display correction rate capable of setting an arbitrary display compensation rate. A control unit may be provided which is provided with a setting unit and which supplies the display unit with a value obtained by multiplying the display compensation rate by the digital amount.

[Operation] In the automatic screw tightener, the first correction unit is adjusted to select the desired amplification factor by static calibration. When it is necessary to match the display value of the display unit with the measurement value measured by the torque wrench, the switching unit is switched to send the output signal of the second amplifying unit to the display unit. Furthermore, the amplification factor at which the average value of the displayed values of a certain number of workpieces is tightened and the average value of the measured values actually measured by the torque wrench is selected is selected by the adjustment of the second correction unit. . After that, a predetermined tightening operation is performed, and the displayed value can be matched with the measured value measured by the torque wrench.

Further, if the output signal of the first amplifying unit is sent to the display unit by returning the switching unit, the output signal of the torque detecting mechanism based on the amplification factor obtained by the static calibration can be immediately obtained. . Therefore, once static calibration is performed, it is not necessary to perform this again, and it is possible to eliminate extra work.

Further, when the display correction rate is set in the display correction rate setting section, a value obtained by multiplying the output signal of the torque detection mechanism by the display correction rate is displayed on the display section. By setting the part to 100%, the output signal of the torque detection mechanism based on the amplification factor obtained by the static calibration can be obtained without performing the static calibration again.

Embodiments Embodiments will be described below with reference to the drawings. In FIGS. 1 and 2, reference numeral 1 is an automatic screw tightening machine, which has a motor 2 and a driver bit 4 which receives rotation of the motor 2 directly via a shaft 3 and integrally rotates. The motor 2 is held by a driver base 7 which is moved up and down by the operation of the lifting drive source 6 via the strain tube 5a of the torque detection mechanism 5, and the motor 2 and the lifting drive source 6 are operated to screw the driver bit 4 into a screw. When a work (not shown) is tightened on a work (not shown), a reaction force generated in the driver bit 4 according to the tightening torque rotates the strain tube 5a. A detection resistor composed of four strain gauges 5b is attached to the outer circumference of the strain tube 5a so as to form a bridge circuit, and a voltage supply source 8 for supplying a reference voltage is provided at the input end of the bridge circuit. It is connected. The detection resistors may not all be composed of the strain gauge 5b. Further, at the output end of the bridge circuit, a first correction section 9a for selecting an amplification factor for zero correction and gain correction via the filter 10 is provided.
The first amplifying unit 9 including is connected. The output signal of the first amplification section 9 is branched in two directions, one of which is sent to the switching section 12 via the first A-D conversion section 11 and further input side of the I / O interface 13 described later. Configured to be sent to. Further, the other output signal is configured to be sent to the switching unit 12 via the second amplification unit 14 provided with the second correction unit 14a for selecting an arbitrary amplification factor and the second A-D conversion unit 16. There is. The switching unit 12 is configured to be switchable from the outside,
The output signal of the first A-D conversion unit 11 is output to the I / O interface 13 when it is on the −D conversion unit 11 side, and the output signal of the second A-D conversion unit 16 is on the second A-D conversion unit side. It is configured to send signals to the I / O interface 13.

The control unit 19 of the automatic screw tightener is a microcomputer, a work start unit 20 via the input side of the I / O interface 13, and a setting unit that stores a voltage value corresponding to a desired tightening torque as a set value. 21 and the torque detection mechanism 5 are connected. Further, the control unit 19 has an I /
An elevating drive source 6 for elevating and lowering the driver base 7 via the output side of the O interface 13, a motor drive unit 24 that sends a command value to the motor 2 and supplies power from the power supply unit 24a to control the rotation of the motor 2. A display unit 25 that displays the output signal of the torque detection mechanism 5 is connected. Further, the control unit 19 is configured to send an A / D conversion command signal to the first A / D conversion unit 11 and the second A / D conversion unit 16 via the I / O interface 13.

Further, as shown in FIG. 3, the control section 19 1) receives an operation start signal from the operation start section 20, and performs an initial reset.

2) A motor drive command signal is sent to the motor drive unit 24 and a descent command signal is sent to the lift drive source 6.

3) The first A-D converter 11 and the second A-D converter 16 have AD
Send a conversion command signal.

4) The output signal of the second A-D converter 16 is compared with the set value stored in the setting unit 21 as a value corresponding to the desired tightening torque, and when they do not match, the process returns to 3).

5) The output signal of the second AD converter 16 is stored as a detection value.

6) Send the motor stop command signal and
Having a stop.

7) Send the display command signal of the detected value to the display unit 25.

8) Send a rising command signal to the lifting drive source 6.

9) End It is configured to operate in the above operation sequence.

When the switching unit 12 is switched to the first A-D conversion unit 11 side, the output signal of the first A-D conversion unit 11 is stored as a detection value instead of the output signal of the second A-D conversion unit 16. To be done.

In the above automatic screw tightener, the switching unit 12 is connected to the first AD
The conversion unit 11 is switched to, and before starting the work, the first correction unit 9a selects an amplification factor by static calibration, and zero correction and gain correction are performed. As a result, the amplification factor that can obtain a theoretical torque value according to the strain amount of the strain tube 5a is selected. At the same time, the setting portion 21 stores a desired tightening torque value as a set value. If the tightening work is performed in this state, a detection value theoretically equivalent to the strain amount detected by the strain tube 5a is detected, and at the time when the output torque of the automatic screw tightening machine 1 surely reaches the desired tightening torque value. It is possible to detect the completion of tightening.

Further, the switching unit 12 is switched to the second A-D conversion unit 16 side, and some tightening is performed every time the type of work changes in this state, and the average value of the display values displayed on the display unit 25 is displayed. And the average value of the measured values obtained by actual measurement with the torque wrench, the second correction unit 14a selects the amplification factor at which the average value of the displayed values matches the measured value. In this state, when the work start signal is transmitted from the work start unit 20, the motor 2 is driven after the initial reset, the lifting drive source 6 is activated, the driver base 7 is lowered, and the driver bit is driven. The screw at the tip of No. 4 is tightened to the work.

As the screw is tightened on the work, the tightening torque applied to the screw becomes a reaction force applied to the driver bit 4, and this is detected as the strain amount of the strain tube 5a by the strain gauge 5b forming the bridge circuit. During this time, the motor 2
At the same time as is driven, an A-D conversion command signal is sent to the second A-D conversion unit 16, and the output signal is compared with the set value corresponding to the desired tightening torque. When the two do not match, an A / D conversion command signal is immediately transmitted to the second A / D conversion section 16 and the comparison is repeated.

When the output signal and the set value match and tightening completion is detected, the detected value at this time is stored, and then a stop command signal is sent to the motor 2 to wait for the motor 2 to completely stop.

When the motor 2 is stopped, the detected value is displayed on the display unit 25. At this time, the output signal of the second A-D converter 16 is a value amplified so as to match the measured value obtained by the actual measurement, so the displayed value is substantially equal to the measured value measured by the torque wrench. And the desired display value is obtained.

After that, the lifting drive source 6 operates, the driver base 7 rises, the original position is restored, and all the operations are completed.

Although the completion of tightening is obtained from the output signal of the torque detection mechanism in the embodiment, the completion of tightening can be detected by detecting the stop of the driver bit if the rotation of the motor is used with an actuating speed reducer such as a differential planetary mechanism. You can Further, in the embodiment, the output signal of the torque detection mechanism is branched in two directions and each of them is amplified by an arbitrary amplification factor to output them alternately. However, the output signal is branched. Alternatively, a display correction factor setting unit may be separately provided and a value obtained by multiplying the output signal by the display correction factor may be displayed on the display unit. In this case, when trying to obtain the output signal with the original amplification factor of static calibration,
A desired output signal can be obtained by setting the display complementation rate to 100%.

[Effects of the Invention] As described above, according to the present invention, the amplification section is connected to the output end of the bridge circuit composed of four detection resistors attached to the strain tube for detecting the reaction force applied to the driver bit, and the output thereof is connected. Since the signals are output in two directions, one of them is directly sent to the other and the other is sent to the switching section through another amplification section, and these are switched by the switching section and alternately displayed on the display section, The amplification part of the can hold the amplification factor that is statically obtained from the calibration, and the other amplification part can change the amplification factor arbitrarily, and it is displayed so that the displayed value and the measured value measured with the torque wrench match. While displaying in the section,
If necessary, the detection output based on the amplification factor obtained by static calibration can be obtained, and there is an advantage that static calibration need not be performed.
Further, since the present invention is provided with the display correction setting unit and is configured to display the value obtained by multiplying the display correction rate set therein by the output signal of the torque detection mechanism on the display unit,
By matching the displayed value with the measured value with a torque wrench, and returning the display correction factor to 100%, the displayed value based on the amplification factor obtained by static calibration can be displayed easily. Not only that, but the display correction rate shows the torque transmission efficiency, and the torque transmission efficiency becomes obvious.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining the whole of the present invention, FIG. 2 is a circuit diagram of a main part of a torque detecting mechanism according to the present invention, and FIG. 3 is a flow chart for explaining an operation of a control unit according to the present invention. 1 ... Automatic screw tightener, 2 ... Motor, 3 ... Connecting shaft, 4 ... Driver bit, 5 ... Torque detection mechanism, 5a ... Strain tube, 5b ... Strain gauge, 6 ... Lift drive source , 7 ... Driver base, 8 ... Voltage supply source, 9 ... First amplification section, 9a ... First correction section, 10 ... Filter, 11 ... First A-D conversion section, 12 ... Switching section , 13 …… I / O interface, 14 …… 2nd amplification section, 14a …… 2nd correction section, 15 ……………………, 16 …… 2nd A-D conversion section, 17 ………… …………, 18 …………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… …, 24 …… Motor drive part, 24a …… Power supply part, 25 …… Display part,

Claims (2)

[Claims] 1. A strain tube and a strain tube for holding a rotatable driver bit by a rotation of a motor on a driver table which is moved up and down by a lifting drive source and detecting a reaction force applied to the driver bit on the driver table. A reaction force type torque detection mechanism having four detection resistors attached to the bridge circuit is attached, and a voltage supply source for supplying a reference voltage is connected to an input end of the bridge circuit, The amount of distortion is detected as an amount of electricity from the output end of the bridge circuit, is sent to a first amplifier having a first corrector that selects an arbitrary amplification factor, and the output signal is branched in two directions. The other is sent directly to the switching unit via the second amplifying unit having a second correcting unit for selecting an arbitrary amplification factor, and the operation of the switching unit causes the second The output signal of the amplifier and an automatic screw driver which characterized in that a control unit to the display unit either of the output signal of the second amplifier. 2. A strain tube and a strain tube for holding a rotatable driver bit by a rotation of a motor on a driver table which is elevated and lowered by an elevation drive source and detecting a reaction force applied to the driver bit on the driver table. A reaction force type torque detection mechanism having four detection resistors attached to the bridge circuit and connected to a voltage supply source for supplying a reference voltage to the input end of the bridge circuit, The distortion amount is detected from the output end of the bridge circuit as an electric amount and is sent to a first amplifying unit having a first correcting unit for selecting an arbitrary amplification factor, and the output signal is converted into a digital amount by the AD converting unit. While converting, a display correction factor setting unit that can set an arbitrary display correction factor is provided, and a control unit that supplies a value obtained by multiplying the display correction factor to the digital amount to the display unit is provided. An automatic screw tightening machine characterized by that.