JPS6133871A - Method of detecting load bearing point - 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 The present invention is a method of tightening bolts using one power tool, and when the bolt axial force reaches near the stress-bearing point, the power tool 1 automatically tightens the bolt. The present invention relates to a stress-proof point detection method for stopping tightening by a tool.

General Branch When tightening a bolt using a powered tool, for example, an electric tool, in order to apply the optimum tightening force to the bolt, some means must be used to control the electric tool. There is a need to.

One known method of controlling the power tool is to detect and control the saturation state of the load current, voltage, etc. of the power tool.
There is one shown in Publication No. 9649. The saturation detection device shown in this publication will be explained below with reference to FIGS. 13 to 15. In the 13th FEJ, V.

is this circuit input voltage, vl is the reference voltage generation circuit (31)
The output voltage v2 is the output voltage of the delayed voltage generation circuit (32), and the saturation voltage value of this output voltage v2 is set larger than the saturation voltage value of the output voltage v1 of the reference voltage generation circuit (31). has been done. (33) is the above voltage V1, V2
Va is the differential detector (33
), (34) is the voltage at the output end of the differential detector (33)
, and v4 is the voltage at the output end of the Schmitt circuit (34).

FIG. 14 is a curve showing an example of the change in voltage Vo with respect to time t, and S is the saturation detection point of the curve. 15th
The figure shows the above voltage V versus time t.

, Vl, v2, v8, and v4. Note that Vx shown in FIG. 15(b) is the Schmitt level voltage of the Schmitt circuit (34).

The operation of the device configured as described above will be explained below. When a voltage Vo as shown in FIG. 14 is applied to the circuit of FIG. 13, before the curve of the voltage Vo reaches the saturation detection point S, the voltages Vi, v2 as shown in FIG.
The curves intersect. Next, if the voltages v1 and v2 are input to the differential detector (33), then v2-vl is amplified to v8 as shown in FIG. 15(b), and the output of the differential detector (33) is voltage at the end. Furthermore, this voltage v
8 becomes the input of the Schmitt circuit (34), and when the voltage V exceeds the Schmitt level voltage Vx, the voltage at the output terminal of the Schmitt circuit (34), which had been zero, suddenly becomes v4. Generates a voltage of Therefore, if the Schmitt voltage Vx is set to the saturation detection point S of the voltage VO as shown in FIGS. can.

In the case of the saturation detection device that is being tested, the maximum value of the input voltage vO differs depending on the volt size, so v, , v2, and v8 also change. Therefore, it is necessary to provide a Schmidt level voltage Vx for each bolt size, which poses the problem of complicating the configuration and making operations when tightening the bolts complicated.

When tightening bolts for the purpose of The point at which the rate of change reaches a predetermined value after reaching the maximum value is defined as a load-bearing point, and the power tool is controlled based on this load-bearing point. According to the present invention, when a bolt is tightened using a single power tool, when the axial force of the bolt reaches near the stress-bearing point, the tightening operation using the single power tool is automatically stopped. Before explaining the present invention in detail, first, the proof point and the yield point that often occurs at the proof point will be explained.

The above-mentioned yield point is determined by, for example, placing a cylindrical test piece cut from a bolt in a tensile tester and pulling it by applying a gentle load only in the axial direction. The load at this time and the state in which the bar-shaped test piece is stretched are recorded using a differential transformer or the like on a recording paper with stress S on the vertical axis and strain ε on the horizontal axis.

Then, as shown in the graph of Figure 11, while stress and strain are in a proportional relationship while elastic strain is occurring in the test piece, the graph becomes a straight line, and when both elastic strain and plastic strain occur, stress and strain Since the proportional relationship is broken, the graph becomes a curve. This point of change is called the yield point (1).

Various stress-strain curves (2) shown in Fig. 11 can be obtained depending on the type of material, presence or absence of heat treatment, etc.
In some cases, as shown in the graph of FIG. 12, the yield point (1) may not clearly appear. In this way, for materials whose yield point (1) is not clearly expressed, there is a proof point (3), which is similar to the yield point (1). This stress-bearing point (
3) The point at which a predetermined amount of residual strain (usually 0.2%) is produced in the test piece when a load is applied in the axial direction of the test piece. The stress that causes this residual strain is called proof stress.

The method of detecting the stress point will be explained below. In order to find the stress point using the method according to the present invention, it is necessary to find the stress-strain curve that occurs in the bolt when the bolt is tightened. It can be converted into the axial force generated on the bolt when the bolt is tightened, and the strain can be converted into the rotation angle θ of the bolt or nut when the bolt is tightened. Therefore, first, as shown in the graph of FIG. 1, the axial force N-rotation angle 0 curve (4) when tightening the bolt is determined. Then, this axial force N-rotation angle 0 curve (4
) is a straight line in the part corresponding to the elastic region of the bolt, and a curve in the plastic region where both elastic strain and plastic strain occur in the bolt. Then, this axial force N-rotation angle 0 curve (
The gradient of 4) is maximum in the straight line portion (4a) and gradually becomes gentler in the curved portion (4b). Therefore, the slope of the curved part (4b) is relative to the slope of the straight part (4a),
The point at which the predetermined amount has decreased is defined as the proof point (3), and this proof point (3
) to control the tightening torque of the power tool. That is, in the axial force N - rotation angle 0 curve (4), (+H/d
t) −n (dI/dt) wax O<n<
1 is defined as a stress-proof point (3), and the tightening torque of the power tool is controlled based on this stress-proof point (3). Note that the optimum value of n may be determined through experiments for each type of bolt used, but normally this value may be set to about 0.5. That is, the gradient of the curved part (4b) of the axial force N - rotation angle 0 curve (4) is the same as that of the straight part (4a).
The point at which the slope becomes 50% is defined as the proof stress point (3).

By the way, when determining the stress point (3) using the above method, it is very difficult to directly determine the axial force N. However, the torque T applied to the bolt by a power tool can be determined relatively easily. Here, the relationship between torque T and axial force N is T = k d #---■.

k: Torque coefficient d: Bolt diameter ■From the formula, N=----■.

d At this time, it can be seen that the axial force N can be easily determined from the torque T because the torque coefficient k and the bolt straightness il d are set in advance depending on the bolt used.

Therefore, as shown in the graph of FIG. 2, the torque knee rotation angle θ curve (5) during bolt tightening is determined. The point where the slope of the curved portion (5b) of the torque knee rotation angle θ curve (5) becomes 50% of the slope of the straight line portion (5a) may be defined as the stress proof point (3).

In addition, as another method for detecting the stress point (3), a current I flowing through a series commutator motor built in a power tool,
The stress point (3) can also be determined from the curve showing the relationship with the current application time t.

That is, there is a proportional relationship between the torque T applied to the bolt by the power tool and the current I flowing through the series commutator motor built into the power tool, and the rotation angle θ and the energization time t to the series commutator motor are also proportional to each other. There is a proportional relationship. Therefore, as shown in the graph of FIG. 3, a current (2) vs. waiting time curve (6) is obtained. Then, the point where the slope of the curved portion (6b) of this current ■-waiting time curve (6) becomes 50% of the slope of the straight line portion (6a) may be defined as the proof point (3).

In addition, when detecting the above-mentioned stress point (3), the current I-turn rotation angle 0 line showing the relationship between the current ■ flowing through the series commutator motor built in the power tool and the rotation angle θ is also used as described above. The proof point (3) can be found in the same way as above.

Next, from the above current I-waiting time curve (6), the proof point (3)
An example of control when calculating the power tool and controlling the power tool will be explained.

FIG. 4 is a block diagram showing the first embodiment, and in the figure (
10) is a sampling circuit that detects changes in the current flowing through the series commutator motor built in the power tool (11) at predetermined time intervals and holds the current value at the start time during that time;
(12) is a differential amplifier for detecting the difference between the current value flowing through the series-wound commutator motor and the current value held in the sampling circuit (10) for each division time, that is, the amount of change in current. be. (13) is an amplifier circuit for smoothing and amplifying the signal corresponding to the amount of change for each division time detected by the differential amplifier (12). (14) is the amplifier circuit (1
(15) is a peak hold circuit that holds the maximum value of the signal smoothed and amplified by (3), and (15) is a peak hold circuit that holds the maximum value of the signal smoothed and amplified by (15).
This is a level generation circuit that outputs a stress point detection level corresponding to 0%. (16) compares the signal output from the amplifier circuit (13) and the stress-proof point detection level output from the level generation circuit (15), and if the two match, the power tool (1
This is a comparator to stop the operation of 1).

In the above configuration, the operation when finding the stress point (3) will be explained. First, when the power tool (11) starts operating, the current value is input to the sampling circuit (10), so the sampling circuit (10) detects changes in the current at predetermined time intervals, and during that time, the current value is input to the sampling circuit (10). Holds the current value.

This value is then sequentially sent to the differential amplifier (12).

In the differential amplifier (12), as shown in the graph of FIG. The amount of change Δ■ is detected and sent to the amplifier circuit (13). The amplifier circuit (13) smoothes and amplifies the signal corresponding to the amount of change ΔI output from the differential amplifier (12), and then outputs the signal to the comparator (16) and the peak hold circuit (14).
). The peak hold circuit (14) holds the maximum value of the signal output from the amplifier circuit (13) and then sends it to the level generation circuit (15). The level generating circuit (15) calculates a stress point detection level (a) corresponding to 50% of the maximum value held in the peak hold circuit (14) and sends it to the comparator (16). In this way, the amplifier circuit (
When the signal (b) corresponding to the amount of change in current ΔI outputted from the level generating circuit (13) and the withstand point detection level (a) outputted from the level generation circuit (15) are input to the comparator (16), ), as shown in Figure 6, compare the two, and if they match, the power tool (11)
stop the operation.

Next, from the above current I-waiting time curve (6), the proof point (3)
The second embodiment when determining the power tool and controlling the power tool is described in the seventh embodiment.
The explanation will be given according to the block diagram shown in the figure.

In the figure, (10a) and (10b) are first and second sampling circuits. The first and second sampling circuits (10a) (10b) detect changes in the current flowing through the series-wound commutator motor at predetermined time intervals and hold the current value at the starting time during that time. As shown in the graph of FIG. 8, the sampling start times of the first sampling circuit (10a) and the second sampling circuit (10b) are shifted by half a cycle.

As shown in the graph of FIG. 9, (12) is the difference in current value that occurs between the first and second sampling circuits (10a) and (10b) due to the time difference at the start of sampling, that is, the amount of change in current △ ■It is a differential amplifier for detecting. Incidentally, the signal corresponding to the amount of change △■ in the current output from the differential amplifier (12) is as shown in FIG.
The polarity or reversed state is detected every half cycle. (17
) is the amount of change in the current output from the differential amplifier (12) △I
(13) is an amplifier circuit that smooths and amplifies the signal output from the double-wave rectifier circuit (17). . (14) is smoothed by the amplifier circuit (13),
A peak hold circuit (15) holds the maximum value of the amplified signal, and (15) is a peak hold circuit (14).
This is a level generation circuit that outputs a stress point detection level corresponding to 30% of the maximum value held by. (16) is the signal output from the amplifier circuit (13) and the level generation circuit (
This is a comparator for comparing the stress point detection level outputted from 15) and stopping the operation of the power tool (11) when the two match.

In the above configuration, the operation when finding the stress point (3) will be explained. First, when the power tool (11) starts operating, the current value is determined by the first and second sampling circuits (10a).
) (10b), the first and second sampling circuits (10a) (10b)
As shown in the graph of the figure, changes in the current are detected at predetermined time intervals with a half-cycle shift between the two, and the current value at the start time is held during that time. This value is then sequentially sent to the differential amplifier (12). In the differential amplifier (12),
As shown in the graph of Fig. 9, the difference in current value occurring between the first and second sampling circuits (10a) and (10b), that is, the amount of change in current Δ■, is detected due to the time difference between the sampling start times of the first and second sampling circuits (10a) and (10b). , the signal corresponding to the amount of change △■ is sent to the amplification circuit (13) via the double-wave rectification circuit (17).
send to The amplifier circuit (13) smoothes the signal sent from the differential amplifier (12) via the double-wave rectifier circuit (17), amplifies it, and sends it to the comparator (16) and peak hold circuit (14). send. Peak hold circuit (1
In step 4), the maximum value of the signal output from the amplifier circuit (13) is held and then sent to the level generation circuit (15). The level generation circuit (15) generates a stress point detection level (30% of the maximum value held in the peak hold circuit (14)).
b) is calculated and sent to the comparator (16). In this way, the amount of change in the current output from the amplifier circuit (13) △
The signal corresponding to I (B) and the stress point detection level (A) output from the level generation circuit (15) are connected to the comparator (
16), the comparator (16) selects the first
As shown in FIG. 0, the two are compared, and if they match, the operation of the power tool (11) is stopped.

When tightening bolts using a power tool, detect the stress point that occurs in the bolt when tightening the bolt, and calculate the tightening torque of the power tool based on this stress point. Since this is controlled, an appropriate tightening axial force can be applied to the bolt without creating a Schmidt level voltage Vx for each bolt size as in the conventional example.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between axial force and rotation angle when tightening bolts with a power tool, Figure 2 is a graph showing the relationship between torque and rotation angle, and Figure 3 is a graph showing the relationship between current and time. It is. FIG. 4 is a block diagram showing the first concrete example of the stress point detection method, FIG. 5 is a graph showing the state at the time of sampling, and FIG. 6 is a graph showing the state when the stress point is detected by a comparator. . FIG. 7 is a block diagram showing the second specific embodiment, FIGS. 8 and 9 are graphs showing the state at the time of sampling, and FIG. 10 is a graph showing the state at the time of stress point detection by the comparator. Figure 11 and 1
Figure 2 is a graph showing the relationship between stress and strain when a tensile load is applied to the test piece in the axial direction. Figures 13 to 1
FIG. 5 is a diagram for explaining the configuration and operation of the saturation detection device. (3') - proof point, (4) - axial force N - rotation angle 8 curves, (4a) - straight line section, (4b) - curved section. Patent applicant Shiga Bolt Co., Ltd. Agent Sho Ehara Hidetake 4 Father\4 Figure 13 Figure 15

Claims (1)

[Claims] (1) When tightening a bolt, the load current, load voltage, load power, or torque of the power tool corresponding to the rate of change of the bolt axial force with respect to the tightening rotation angle, and either the tightening rotation angle or the tightening time. It is characterized by detecting the related characteristics, determining the point at which the rate of change reaches a predetermined value as the rate of change reaches a predetermined value, and controlling the power tool based on this stress-bearing point. A stress-bearing point detection method.