JPS629872B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic sensing method and an improvement in an electromagnetic sensor for sensing a conductor in a non-contact manner.

It is well known that the proximity of a conductor to a coil is detected by measuring a change in output due to a change in Q of the coil.

On the other hand, it is also well known that the value of the inductance of a coil varies depending on the dimensions of the coil, and therefore a change in the dimensions of the coil due to a temperature difference in the coil will change the value of the inductance.

Therefore, in such electromagnetic sensing, a problem has been how to reduce measurement errors due to temperature changes in the coil.

As a means to solve this problem, it has been proposed to cool the coil with a refrigerant such as water to maintain a constant low temperature. However, with this method, it is necessary to provide a water jacket to the measurement coil, and a pipe to supply cold water to this water jacket is required, which not only makes the structure complicated, but also causes the pipe to become an obstacle. There is. Furthermore, fine control of the coil temperature cannot be desired.

Therefore, the present invention aims to provide an electromagnetic sensor in which the above-mentioned problems are solved by heating the coil and keeping it at a constant high temperature.

Other objects and features of the invention will become apparent from the more detailed description below.

First, a part of an embodiment of the invention will be explained with reference to FIG. Although this embodiment shows a case where an electromagnetic sensor is integrally provided with a torch of a known automatic welding robot, the present invention is not limited to this embodiment.

1 is an electromagnetic coil in which a detection coil 1a and a temperature compensation coil 1b are wound in series around a heat-resistant winding core 1c. Both coils 1a and 1b had an inductance of several tens of μH.

Reference numeral 2 denotes a non-induction heater in which an electric resistor 2b is provided on a heat-resistant bobbin 2a on the outer periphery of the coil 1. The resistor 2b has electrode terminals 2c and 2d at both ends of the bobbin 2a.
A thin film is evenly coated in between. As shown in FIG. 2, the shaft 2b may be provided with a resistance wire 2b reciprocating in the axial direction of the bobbin 2a between the terminals 2c and 2d of the bobbin 2a. Furthermore, as shown in FIG. 3, the resistance wire 2b may be folded in half and wound between the terminals 2c and 2d of the bobbin 2a. In short, the resistor 2b is provided without induction, including other known methods.

Although the details are not shown, the coil 1 and the heater 2 are integrated to form a heater-equipped electromagnetic coil CL.

T is a welding torch held at one end of the automatic welding robot.

W is a workpiece held at the other end of the automatic welding robot. In this embodiment, the work W is a steel plate having a developed weld line WL.

Then, the torch T is integrally accompanied by the electromagnetic coil CL, and the torch T is connected to the workpiece W at the orthogonal coordinates X, Y, Z.
The position is controlled by the action of a well-known robot in the direction. In more detail, Torch T
The X direction is controlled by another well-known welding line sensor (not shown) so that it is directly above the welding line WL in the Y direction, and the Y direction is controlled by a preset program.
It can be moved at a certain speed in a direction. Torch T's Z
Direction position control is performed using the electromagnetic coil according to the present invention.
Control is performed by the output of CL to keep the gap H between the lower end of the coil CL and the surface of the workpiece W constant.
These will be further explained in detail with reference to the circuit diagram of FIG. In the configuration of FIG. 4, the same parts as those in FIG. 1 are given the same reference numerals, and the explanation thereof will be omitted.

_S1 is a power source for the heater 2.

C ₄ and C ₂ are AC resistances that constitute the sides of the AC bridge B together with the coils 1a and 1b.

_S2 is Bridge B's AC power supply. In this example, it was set to 1MHz.

_A1 is an amplifier that inputs the output of Bridge B.

When the switching means SW is in the normal position shown in the drawing, the AC bridge B is connected as shown in the drawing.

_S3 is a DC power supply, which is connected in series with the coil 1a and amplifier _A2 by switching the switching means SW.

_S4 is another DC power source, which is connected in series with the coil 1b and amplifier _A3 by switching the switching means SW.

SC is a control means for the power supply S ₁ , for example, the power supply S ₁
It is configured to be able to control on/off or control the voltage.

RL is a relay, which is configured to switch the switching means SW (in this embodiment, a two-pole, double-throw switch).

CO ₁ , CO ₂ , CO ₃ are amplifiers A ₁ , A ₂ , A ₃ respectively
An A/D converter connected to the output of

DRZ is a driving means for moving the coil CL in the Z direction, and is composed of, for example, the rotational power of a threaded rod screwed into a nut integrated with the coil CL.

CN is a well-known computer, and includes a central processing unit CPU, memory ME, and the like. A control means SC, a relay RL, A/D converters CO ₁ , CO ₂ , CO ₃ , and a drive means DR are connected to the bus BU of the computer CN by well-known means to obtain an interface.

The operation of the embodiment having the above-mentioned configuration will be described below.

First, the output value of Bridge B (the output value of converter CO 1 is a function of this) is determined by the temperature difference between coils 1a and 1b (the difference between the outputs of converters CO _{2 and} CO ₃ is a function). That is, a correction value for how to correct the value of the sensed gap H is determined in advance by calibration using a known method, and this correction value is stored in the memory ME.

Regarding relay RL, for example, 1 minute
A system program to be run at a rate of seconds is stored in the memory ME.

As for the control means SC, a system program is provided that can control the power supply _S1 so that the coil 1a is maintained at the temperature set in the computer CN in advance (that is, the output value of the converter _CO2 is kept at a certain constant value). Store in memory ME.

Regarding the drive means DRZ, the Z of the coil CL is adjusted so that the gap H becomes a predetermined constant value.
A system program is stored in the memory ME to control the directional position.

Furthermore, the system program controls the driving means DRX in the X-axis direction and the driving means DRY in the Y-axis direction (not shown) so that the torch T follows the welding line WL and moves from one end of the welding line WL to the other end. and the user program is stored in the memory ME.

After completing the above preparations, activate the circuit shown in FIG. 4 and put the computer CN into auto mode.

In the illustrated state, the output value of Bridge B is sent to the computer via amplifier A ₁ and converter CO ₁ .
Enter CN. Then, relay RL operates for the above-described certain period of time, switching means SW switches, and outputs are generated from amplifiers A ₂ and A ₃ . The output value of the amplifier A ₂ is a function of the DC resistance value of the coil 1a, that is, the temperature of the coil 1a, and the output value of the amplifier A ₃ is a function of the DC resistance value of the coil 1b, that is, the temperature of the coil 1b. If these two output values are equal, that is, the input values to the computer CN from which these output values are digitized are equal, then the output from the converter CO ₁ described above to the computer CN is the same.
The input value to CN is exactly a function of the gap H.
Then, in order to maintain this gap H at a predetermined constant value, the driving means is
DRZ is activated.

If there is a difference in the digital input values from the converters CO ₂ and CO ₃ , this means that there is a difference in temperature between the coils 1a and 1b, and according to the program described above, the input from the converter CO ₁ is changed to the computer.
Corrected in CN.

Furthermore, in order to keep the temperature of the input from the converter CO ₂ constant, that is, the temperature of the coil 1a, the power supply S ₁ is controlled by the control means SC by the well-known action of the computer CN according to the program described above, and the temperature of the coil 1a is controlled by the control means SC. Temperature is controlled to be constant.

In this way, the torch T, which is the heat source, is
Coil 1 regardless of whether it is near CL
a, 1b are controlled to a constant temperature, and even if there is a temperature difference between the two coils 1a, 1b, this is corrected and the workpiece W is always kept with an accurate gap H.
You can understand what I mean. In the inventor's experiment, when each configuration was selected so that the temperature of the coil 1a was constant at 250°C and the gap H was controlled to be constant at 5 mm, the operating error was ±
It was within 0.3mm.

Furthermore, it will be understood that in the above-mentioned embodiments, it is also effective to measure the gap H instead of implementing the present invention so that the gap H is constant.

In addition, the temperature of the coils 1a and 1b was measured by measuring the DC resistance value of each individual coil, but this was also done by measuring the DC resistance of either coil alone and the series combined DC resistance of both coils. It's okay.

To measure the temperature of the coils 1a and 1b, a known temperature sensor may be embedded in the coils instead of measuring their direct current resistance.

The power source S ₁ may be a direct current instead of an alternating current. In addition, the power supplies S ₃ and S ₄ are not direct current, but are substantially connected to the coils 1a,
A low frequency AC power source capable of measuring the DC resistance of 1b may be used.

In addition, an electronic circuit that performs the same function as described above without using the computer CN as a temperature correction means.
CT may also be connected.

This circuit CT will be described in detail below with reference to FIG.

_A4 is a known linearization amplifier that inputs the output value _A11 of the amplifier _A1 , and the value of the gap H between the conductor W to be detected and the coil 1a and the output value _A41 of the amplifier _A4 are linear functions. Amplifier _A4 is configured so that the relationship is as follows.

BI is a known variable bias circuit that inputs the output of the amplifier _A2 , and is configured to have a variable bias level.

_A5 is a variable amplifier that inputs the output of the bias circuit BI.

_A6 is a known variable differential amplifier that inputs the output value of amplifier _A3 .

_AD1 is a first adder that receives the output of amplifier _A5 and the output of amplifier _A6 .

_H1 is a known first hold circuit that inputs the output of amplifier _A4 . _H2 is a known second hold circuit that inputs the output of the adder _AD1 .

_AD2 is a second adder that receives the outputs of the hold circuits _H1 and _H2 .

T is a known timer control circuit, which is designed to output signals instructing the relay RL, hold circuits H ₁ , H ₂ , and adder AD ₂ to operate at the timing shown in FIG. 6.

Next, the operation of the above embodiment will be described.

In the illustrated state, the switching means SW in FIG.
It is assumed that this is a normal state and that an AC bridge circuit B is constituted by coils 1a and 1b and AC resistors C ₁ and C ₂ . The coil 1a is close to the conductor W at a gap H. Therefore, the impedance of coil 1a is changing, and the amplifier
The output value A ₁₁ of A ₁ changes in response to a change in the gap H. The state of this change becomes a curve as shown in FIG. 7A. The output of this amplifier A ₁ is amplifier A ₄
The output value A ₄₁ is a value in a linear relationship with respect to the gap H, as shown in FIG. 7B. On the other hand, from the control circuit T, a command signal is usually given to only the hold circuit _H1 to activate it, and the output of the amplifier _A4 mentioned above is held in the circuit _H1 .

On the other hand, as time passes, the relay from circuit T
A command signal for RL is output, and the accompanying means SW is switched downward in the figure. At this time, amplifier A ₂
is output as a function of the temperature of coil 1a, and amplifier A ₃
is output as a function of the temperature of the coil 1b. When the output value A ₂₁ of this amplifier A ₂ is input to the variable bias circuit BI, the ambient temperature (for example, 25°C) is input to the circuit BI.
Depending on the bias level set in relation to , the output is modified by the set level so that the output value BI ₁ from the circuit BI becomes zero at 25°C, for example, as shown in Figure 7. Output. Furthermore, the output from this circuit BI is input to amplifier _A5 . The input value of the amplifier _A5 is amplified by the gain set in the amplifier _A5 and outputted as _A51 in FIG. 7E. This gain set is determined by the amplifier
It is defined so that the output value of _A4 can be corrected for temperature.

At the same time, the output values of amplifiers A ₂ and A ₃ are
Enter _A6 . This differential output value is amplified according to the gain set in amplifier _A6 . This set of gains is determined so that the output of the amplifier _A4 can be temperature-compensated, as will be made clear in the description of the temperature compensation function described later.

And each output of amplifiers A ₅ and A ₆ is connected to adder AD ₁
is added by.

Furthermore, with the passage of time, before the command to relay RL is erased, a command signal to hold circuit _H2 is output and hold circuit _H2 is activated, and the output added by adder _AD1 described above is accordingly output. The value is held in circuit _H2 .

When the command signal to the relay RL is erased, the bridge circuit _B is configured by the return of the means _SW in FIG. Amp A ₄
The output value of is held in circuit _H1 again.

Furthermore, the adder AD ₂ is activated by a command signal to the adder AD ₂ , and the output values of the hold circuits H ₁ and H ₂ are added to obtain a temperature-compensated output value.

To further explain this temperature compensation in detail with reference to Fig. 6, in this figure _H11 represents the change in the output of the hold circuit ^H1 with respect to the change in the temperature of the coil 1a when the temperatures of the coils 1a and 1b are the same. , and H ₁₂ indicates a change in the output with respect to a change in the temperature of the coil 1a when the temperatures of the coils 1a and 1b are different. On the other hand, H ₂₁ indicates the output of the hold circuit H 2 when the temperatures of the coils 1a and 1b are the same, that is, when the output of the amplifier A ₆ is zero, and H ₂₂ indicates the output of the hold circuit H ₂ when the temperatures of the coils 1a and 1b are the same. The output of the hold circuit _H2 is shown when the temperature is different.
And _A61 indicates the output of amplifier _A6 . In the above description, the gain of amplifier A ₅ is such that the output curve denoted H ₁₁ is compensated by the output curve denoted H ₂₁ to maintain a constant output AD ₂₁ of adder AD ₂ with respect to temperature changes. It is adjusted in advance so that Furthermore, the gain of amplifier A ₆ is H ₁₂
The output curve shown by is compensated by the output curve shown by H ₂₂ , and the output AD _{21 is adjusted in advance so that it becomes a constant output AD 21} with respect to changes in temperature. It will be understood that these adjustments vary depending on the material and dimensions of the conductor W, the gap H to be accurately sensed, and the like.

It will also be appreciated that the output of adder AD ₂ is thus a temperature compensated output.

Still another embodiment will be described with reference to FIG. In this embodiment, the same components as those in FIG. 4 are given the same reference numerals, so that the overall structure will be clear from the illustration.

In this embodiment, the AC bridge B is the same as the embodiment in FIG. 4, but the coils 1a,
The temperature of the heater 1b is not measured, and a constant current continues to flow through the heater 2 as well. In this case, it is a simple form that can be put to practical use when the ambient temperature is almost constant, and it is clear from the above explanation that the gap H can be determined from the output value of amplifier _A1 , so details will be given below. Omitted.

Still another embodiment will be described with reference to FIG.

Coil CL in this example is the primary coil
The secondary coils 1a and 1b are differentially wound with respect to C ₃ to form a differential transformer T. _S5 is the AC power supply for the primary coil _C3 .

The heater 2 is provided in accordance with the previous embodiment.

Furthermore, amplifier A ₁ connected to both ends of the secondary coil
It is clear from the well-known operation of the differential transformer T that the gap H can be measured by the output value of . Further, it will be understood from the previous embodiments that the heater 2 keeps the coil C at a constant temperature regardless of the ambient temperature, thereby reducing errors due to temperature.

Still another embodiment will be described with reference to FIG.

The coil CL is only a coil 1 consisting of coils 1a and 1b, and does not particularly include a heater 2. Since the coils 1a and 1b also serve as heaters, their material is, for example, nichrome wire. resistance
The bridge circuit B is formed by C ₁ and C ₂ , the coils 1a and 1b, and the power supply _S2 , and the output thereof is input to the amplifier _A1 , as in the previous embodiment. However, in this embodiment, the resistors C ₁ ,
DC blocking capacitors CD ₁ , CD 2 and CD 3 , CD ₄ are interposed between C ₂ and power source S ₂ and coils _1a and _1b . S ₁ is a known variable DC power supply that supplies DC voltage to coils 1a and 1b;
A known AC blocking filter F ₁ is connected between a and 1b,
_F2 is mediated. Further, a bias capacitor CD ₅ is connected to both ends of the DC power supply S ₁ . SE is a well-known temperature sensor embedded in the coil 1, and the output of the sensor SE is input to a well-known voltage control circuit SC that changes the output voltage of the power supply _S1 .
Control _S1 .

The operation of this embodiment will be described below. As in the previous embodiments, the AC bridge circuit B inputs the difference in AC resistance between the coils 1a and 1b, that is, the function of the gap H, to the amplifier _A1 . The gap H is known from the output value, which is the same as in the previous embodiment. Further, the coils 1a, 1b are heated by the power source _S1 , the temperature of which is detected by the sensor SE, and the power source _S1 is controlled to keep the temperature of the coils 1a, 1b substantially constant. In this case capacitor CD ₁ ,
It will be understood that CD ₂ , CD ₃ , CD ₄ , CD ₅ and filters F ₁ and F ₂ do not affect the power supplies S ₁ and S ₂ and do not interfere with the operation of circuit B.

In addition to the above-mentioned embodiments, the technical scope of the present invention also includes substitutions of equivalent components within the scope of the technical idea of the present invention.

Since the present invention is as described above, it has the following remarkable effects.

(I) Since the electromagnetic coil is heated, it is not only possible to easily control the electromagnetic coil to a nearly constant temperature and reduce errors caused by temperature changes in the electromagnetic coil, but also to reduce errors caused by temperature changes in the electromagnetic coil. Since refrigerant wiring is not required and, for example, a current supply wire for the heater can be used, the electromagnetic coil can be easily moved.

() More accurate measurements can be obtained by measuring the temperature of the electromagnetic coil and controlling the heating. Moreover, if this temperature measurement is carried out by measuring the direct current resistance of the coil, the structure can be made simple and compact.

() More accurate measurements can be expected if a bridge circuit is constructed by adding a temperature compensation coil in addition to the detection coil as the electromagnetic coil.

() If a non-induction heater is used as the heater, which is installed on the bobbin surrounding the outer circumference of the electromagnetic coil, it will not only be possible to heat the electromagnetic coil almost uniformly, but also to reduce the influence of external heat sources (for example, welding torches). Since there is no induction, there is no effect on the output of the electromagnetic coil.

() If a computer is used as the temperature correction means, other control means (for example, control of an automatic welding robot) can also be controlled.

[Brief explanation of the drawing]

1 to 4 show an embodiment of the present invention,
FIG. 1 is a perspective view of essential parts, FIGS. 2 and 3 are perspective views showing various embodiments of the heater, and FIG. 4 is an overall circuit diagram. 5 to 7 show other embodiments, and FIG.
The figure is a circuit diagram showing different parts from FIG. 4, and FIGS. 6 and 7 are diagrams for explaining the operation. Figure 8, Figure 9, Figure 1
0 are circuit diagrams showing still other embodiments. 1... Electromagnetic coil, 1a... Detection coil, 1b...
Temperature compensation coil, 2... Non-induction heater, 2a
…Bobbin, W…Work (conductor), CN and CT
...Temperature correction means, B...AC bridge circuit, SW...
Switching means, _S3 , _S4 ...DC power supply, _A1 , _A2 , _A3 ...Amplifier, _CD1 , _CD2 , _CD3 , _CD4 ...DC blocking capacitor, _F1 , _F2 ...AC blocking filter.

Claims (1)

[Scope of Claims] 1. An AC bridge circuit having a detection coil and a temperature compensation coil on two sides, a heater for heating both coils, and a DC resistance measuring circuit for each of the coils connected by a switching means. An electromagnetic sensor comprising temperature correction means for correcting the output value of the AC bridge circuit based on the output value of the DC resistance measuring circuit. 2. The heater is a non-induction heater provided on a heat-resistant bobbin surrounding the outer periphery of each coil.
An electromagnetic sensor according to claim 1. 3. The electromagnetic sensor according to claim 1, wherein the DC resistance measuring circuit includes a coil, a DC power supply, and an amplifier connected in series. 4. The temperature correction means is a computer that stores a correction value based on the output value of the DC resistance measuring circuit and corrects the output value of the AC bridge circuit using this correction value.
Electromagnetic sensor described in section. 5 An AC bridge circuit with a detection coil and a temperature compensation coil on two sides, a DC blocking capacitor interposed between the AC power supply and AC resistance on the other two sides, and an AC blocking filter interposed at both ends of the coils on the two sides. An electromagnetic sensor comprising a DC power supply connected to the coils, and heating both coils by superimposing DC current.