JPS6032804B2 - electromagnetic sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic sensor capable of correcting measurement errors due to temperature.

In the conventional electromagnetic sensor that senses the guiding fin body,
For example, consideration has been given to reducing the output error caused by a rise in sensor temperature by using a differential winding for the output coil or by providing a temperature compensation coil in addition to the detection coil. However, when such an electromagnetic sensor is exposed to high temperatures, for example when the sensor is installed near the welding torch in an automatic welding robot, it is necessary to correct the output error due to the rise in sensor temperature. was not sufficient, and the error could not be ignored in practice. Accordingly, it is an object of the present invention to provide an electromagnetic sensor that detects the temperature of an electromagnetic coil, compensates for errors corresponding to the temperature, and always obtains accurate detection output.

Other objects and features of the invention will become apparent from the more detailed description below. First, the embodiment shown in FIG. 1 will be described. C, is a detection coil, and C2 is a temperature compensation coil. Although details of the coils C, C2 are not shown, each coil has an inductance of several tens of rH.
R represents the equivalent DC resistance of the coil C, and R2 represents the equivalent DC resistance of the coil C2. Z and Z are AC resistors that form the basis of the AC bridge circuit BA together with the coils C, , C2.

R3 and R4 are DC resistors that constitute a DC bridge circuit BD together with the coils C, , C2.

S, is the AC of the AC bridge circuit BA (in this example, I
S2 is a constant current DC power supply for the DC bridge circuit BD.

SW is a switching means for switching each side of the bridge circuit so that bridge circuits BA and BD having two common sides of the coils C, , C2 can be selectively configured.

In this embodiment, it is a two-pole, double-throw switch that is normally tilted back to the right as shown in the figure and switched to the left by the operation of relay RL. A, is the first circuit that inputs the output of the bridge circuit BA.
The amplifier, n, is a second amplifier that inputs the potential across the coil C, and n, a variable amplifier that inputs the output of the bridge circuit BD.

is amplifier A, is output value A, . This is a known linearization amplifier that inputs A4. The amplifier is constructed such that the relationship is a linear function.

RE is a known rectifier circuit that receives the output of the amplifier A4.

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 receives the output of the bias circuit BI. AD is a first adder that inputs the output of the amplifier A5 and the output of the amplifier A5.

1 is a known first held circuit that inputs the output of the rectifier circuit RE.

The ratio is determined by the adder AD. This is a known second hold circuit that inputs the output of the circuit. AD2 is a second adder which inputs the output of the hold circuits 1, 2.

T is a known timer control circuit, and relay RL
A signal instructing the operation of the hold circuit 1, 2, and adder AD2 is outputted at the timing shown in FIG.

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

In the illustrated state, the switching means SW is in a normal state, and an AC bridge circuit BA is constituted by coils C, C2 and AC resistors B and Z2.

And, Koino is close to the guide crab body W on the interstitial day. Therefore, the impedance of coil C, changes, and the output value A, . changes in response to changes in the interstitial day. The state of this change becomes a curve as shown in the figure. The output of this amplifier A, is input to the amplifier, and its output value A4, is a value in a linearized relationship with respect to the gap date as shown. Furthermore, the output of amplifier A4 is rectified by rectifier circuit RE. On the other hand, from the control signal T, a command signal is normally applied and activated only to the hold circuit 2, and the power of the circuit RE described above is held to the circuit 2. On the other hand, as time passes, a command signal for the circuit T click relay RL is output, and the accompanying means SW
switches to the left in the figure, and the bridge circuit BA switches to BD.

At this time, the DC voltage difference across the coil C is input to the amplifier, and the output of the DC bridge circuit BD is input to the amplifier. Since the current flowing through coil C is constant,
The output value A of the amplifier A2 is a linear function determined by the DC resistance value of the coil, that is, the temperature of the coil C. When the output value of this amplifier A2 is input to the variable bias circuit BI, depending on the bias level set in the circuit BI in relation to the ambient temperature (for example, 25°C), the output value from the circuit BI at 25°C, for example, B1, so that becomes zero,
The output is corrected by the set level and output. Furthermore, the output from this circuit BI is input to an amplifier A5. The input value of the amplifier AP is amplified by the gain set in the amplifier A5 and output. This set of gains is determined so that the output value of the circuit RE can be temperature-compensated, as will be made clear in the description of the temperature compensation effect described later. At the same time, the output value of the bridge circuit BD is input to the amplifier A3.

In this case, if the coils C and C2 are at the same temperature, the output value of the amplifier A3 will be zero, but if there is a temperature difference, the output value will be positive or negative depending on which coil is hotter.
This world power value is amplified according to the gain set in amplifier A3. This set of gains is determined so that the output of the amplifier A5 can be temperature-compensated, as will be made clear in the description of the temperature compensation function described later. The respective outputs of amplifiers A3 and A5 are then added by adder AD.

Furthermore, with the passage of time, before the command to relay RL is erased, a command signal for the hold circuit ratio is output, the hold circuit is activated, and the output value added by the adder AD, described above, becomes It is held at the circuit ratio.

When the command signal for the relay RL is erased, the bridge circuit BA is configured by the return of the means SW, and the hold circuit BA is also activated. The hold circuit 1 is activated by the command signal to 1, and the output value of the circuit RE resulting from the output of the restored bridge circuit BA is held in the circuit 1 again.

Further, by a command signal to adder AD2, adder A
D2 is activated and the output value of the hold circuit is added to obtain a temperature compensated output value.

This temperature compensation can be further explained in detail with reference to FIG. 3. In this figure, days, . indicates the change in the output of the hold circuit 1 with respect to the change in the temperature of the coil C, when the temperature of the coils C, , C2 is the same, and 2,2 is the change in the output of the hold circuit VC, ,
3 shows the change in the output with respect to the temperature change of the coil C, when the temperature of the coil C2 is different.

On the other hand, the ratio , represents the output output of the hold circuit 2 when the temperatures of the coils C, , C2 are the same, that is, when the output of the amplifier A3 is zero,
, , shows the output of the hold circuit 2 when the temperatures of C2 are different. The A nail indicates the output of the amplifier A3. In the above explanation, the gain of the amplifier is . The output curve shown by is compensated by the output curve shown by the ratio , and is adjusted in advance so that the output AD2 of the adder AD2 is constant against changes in temperature. Furthermore, the gain of amplifier A3 is set such that the output curve denoted by 2,2 is compensated by the output curve denoted by &2, resulting in a constant output ADa with respect to temperature changes.
It is adjusted in advance. It will be understood that these adjustments will vary depending on the material and dimensions of the guide body W, the gap date on which accurate sensing is desired, etc. Thus, the output of the adder AD2 is input to a position control means (not shown) that moves the coil C close to and away from the conductor W, thereby making it possible to keep the gap constant.

In this example.

The coils C, , C2 are installed near the skin G welding torch of the automatic welding robot, and the iron plate of IQ thickness to be welded is connected to the conductor W.
When the coils were aligned with a gap of 3 ribs between the iron plates, the temperature of the coils eventually rose to about 20°C, but the alignment error was within 0.2 ribs. In the embodiment shown in FIG. 1, instead of the circuit CT as the temperature compensation means, the computer is connected by known means, that is, an A/D converter and a relay connected to each of the amplifiers A, A2, and A3. If the RL and the position control means (not shown) are interfaced with a computer by known means, the same effects as those of the above-mentioned embodiments can be achieved.

This will be explained in detail with reference to the flowchart shown in FIG. First, the operator enters the measurement conditions (conductor W and gap day conditions) and temperature coefficient T (t
) and the gap coefficient f(1) are stored.

The coefficients T(t) and f(1) are determined by the output values A, . The power coefficients T(t) and f(1) are determined practically. That is, the coefficient T(t) is calculated for each temperature difference between the case where there is no difference in temperature between the coils C and C2 and the case where there is a difference in temperature. Also, the temperature of the coil C, from the output signal value A2 of the amplifier A2, and the temperature difference between the coils C and C2 from the output value A3 of the amplifier A3 are determined through experiments, and their coefficients are also memorized. .

Then, as a step in the computer program, it is determined whether the output of the 'A' amplifier is zero or not.

[〇- If it is zero, there is no temperature difference between the coils C and C2, so the temperature of the coil C is determined by the coefficient from the output value A2 of the amplifier A2. Further, the corresponding temperature coefficient T(t) is selected and determined from the measurement conditions inputted in advance and the temperature of the coil C. If it is not zero in step 1, then calculate the temperature of coil C from the table using the coefficient, for example, from the output value A2 of the amplifier, and then calculate the temperature of coil C, from the output value A of the amplifier. The temperature difference ΔT between C2 and C2 is determined, for example, by a coefficient, and is determined from a table.

Furthermore, the corresponding temperature coefficient T(t) is selected and determined from the measurement conditions input in advance, the temperature of the coil C, and the temperature difference ΔT. 8 Select and find the gap coefficient f(1) from the measurement conditions in this sensing.

The output value A, . have coefficients T(t) and f(1
) to find the gap date.

In the embodiment shown in FIG. 1, the input coil ' to the amplifier is set at both ends of the coil, but it may also be set at both ends of the series of the coils C and C2. In this case, the output value Aa of the amplifier is , the average value of the temperatures of coils C, and C2.

Then, in the following circuit, a correction curve may be determined based on this value. Furthermore, in the embodiment of FIG. 4 in which a computer is used, each coil C, . C
It is obvious that the temperature of 2 can be calculated by calculation. Furthermore, in addition to storing the aforementioned coefficients in the computer,
It will be understood that it would also be possible to store the values of gap days corresponding to each condition as a table. Next, another embodiment that does not use a compensation coil as a coil will be described with reference to FIG.

C3 is a primary coil to which an AC voltage is applied by the AC power source S and the switch.

C and C are detection coils, and C4 and C are coils wound over the coil C3. A differential transformer T is constituted by the coils C, C3, and C4. SW
is a switch as a switching means, and RL is a relay for switching this switch. R, , R4 are equivalent DC resistances of the coils C, , C4, respectively. R3,R
Reference numeral 5 denotes a DC resistor forming two sides of the DC bridge BD, which is formed when the means SW is switched from the one shown in the figure and the switch 1 is opened, and S2 is a DC power supply for the bridge BD. A, , A3 are amplifiers. When the conductor W approaches the differential transformer T, its differential output is input to the amplifier A, where it is amplified and an output value A,2 is output.

When the amplifier A3 is switched to the bridge BD, the difference in resistance value between the DC resistances R and R4, that is, the coil C,
A function value of the temperature difference between C4 and C4 is output. The amplifier is
The value of the DC resistance R, that is, the function value of the temperature of the coil C, is output. The outputs of these amplifiers A, A2, A3 may be connected to the circuit CT shown in FIG. 1, or may be connected to a computer and processed according to a program as shown in FIG. That will be understood.

Furthermore, in this embodiment as well, the temperature of the coil is
, and C4 may be measured. In addition, in this invention, an electromagnetic coil as a sensor,
For example, as shown in FIG. 6, there is only a detection coil C without a compensation coil or a differential winding coil, and this coil C,
Alternatively, the AC power supply S and the DC power supply S2 may be selectively connected to each other by a switch SW, and the output value of the amplifier may be temperature-corrected by the output value of the amplifier A2 in accordance with the embodiment described above.

Further, in the above embodiment, the DC power source used for measuring the DC resistance of the coil may be a low frequency AC power source that provides substantially the same effect. Various other modifications within the technical scope of the present invention are also included within the technical scope of the present invention. Since this invention is as described above,
This has the following remarkable effects.

(1) The temperature of the electromagnetic coil that detects the conductor is corrected for the detection error caused by changes in the impedance of the coil due to temperature. When used in a sensor for detecting an object to be welded near a torch, accurate sensing can be expected regardless of the temperature of the coil.

(0) To detect the temperature of the electromagnetic coil, if we use the short-time switching method to find the DC resistance of this coil,
In particular, it is not necessary to provide a temperature detection sensor.

(m) In the case where a temperature compensation coil is attached to the detection coil to form a bridge, the short-time switching method is used to alternately switch between the AC bridge circuit and the DC bridge circuit. Not only does it not require a temperature detection sensor, but one of the coils is close to the heat source, and initially both coils were at the same temperature as the ambient temperature, but now the temperature of the coil closer to the heat source is Accurate temperature correction is possible even if the temperature rises first.

(W) In the case of the detection coil using a differential transformer, the switching means is used to alternately switch between the differential transformer circuit and the DC bridge circuit, so there is no need to provide a temperature detection sensor in the sensor itself. (m)
Similarly, accurate temperature correction can be made even if there is a temperature difference between the coils.

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention, in which FIG. 1 is a circuit diagram, FIG. 2 is a timer output diagram, and FIG. 3 is a temperature compensation diagram. FIG. 4 is a flowchart showing another embodiment. Fifth
The figure is a circuit diagram of yet another embodiment. FIG. 6 is a circuit diagram of still another embodiment. C. ...Detection coil, C
2...Temperature compensation coil, C3...Primary coil, C4
...Differential winding coil, SW...Switching means, BA...
...DC bridge circuit, BD...AC bridge circuit, CT...temperature compensation means, T...
...Differential transformer. Figure 2 Figure 3 Figure 6 Figure 4 Figure 5

Claims (1)

[Claims] 1. An AC bridge circuit and a DC bridge circuit that are selectively configured by a switching means, with the detection coil and the temperature compensation coil on two common sides, and the output of the DC bridge circuit and the detection coil. An electromagnetic sensor comprising a DC resistance measuring means of the detection coil to which an output is connected, and a temperature compensating means to connect an output of the DC resistance measuring means and an output of the AC bridge circuit. 2. The electromagnetic sensor according to claim 1, wherein the coil connected to the DC resistance measuring means is one of the two coils. 3. The electromagnetic sensor according to claim 1, wherein the coils connected to the DC resistance measuring means are both the coils. 4. A primary coil, a detection coil further wound around this primary coil, a differential winding coil for this, a differential transformer circuit constituted by these coils, and the detection coil and differential winding coil on two sides. switching means for selectively connecting the detection coil and/or the differential winding coil to the DC bridge circuit; temperature compensation means for compensating with the output values of the DC bridge circuit and the DC resistance measuring means;
An electromagnetic sensor equipped with