JPH0252961B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that uses high-frequency overcurrent to non-contactly detect the position of an edge of a conductive metal body or its approach.

Advances in technology in the mechanical industry are remarkable, and automated systems that combine machines and electronics, such as robots, have come to occupy an extremely important position. In such automated systems, various detection devices play important functions, but metal object position detection devices are especially needed for a wide range of applications, including eddy current type, capacitive type, formula,
Magnetic type and other types are known. However, when used for the purpose of detecting the moving direction position of the edge of a metal body moving across the detection area of the detection device or its approach, the conventional detection device has the following problems. was.

First, with the eddy current type, considerable errors occur if the separation distance between the detection section (probe) of the detection device and the metal object to be detected is not maintained accurately.
Furthermore, in the capacitive type, errors occur due to the influence of moisture and oil adhering to the detection section or the surface of the metal object to be detected. Furthermore, the magnetic type has a limitation in that it is necessary to add a magnetic body to the object to be detected.

The present invention was made to solve the problems of the conventional device, and the detection accuracy is not easily affected by the distance between the detection unit and the detection target.
Another object of the present invention is to provide an edge detection device for metal bodies that is not affected by moisture or oil adhering to these objects, can be detected even in water or oil, and does not require the addition of a magnetic body to the detection target. shall be.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on drawings showing embodiments thereof.

FIG. 1 is a block diagram of the apparatus of the present invention. Reference numeral 1 denotes a probe which should face the metal plate A to be detected, and has three detection coils 21, 22, 23 and resistors 3, 3, 3 built therein. Each detection coil 2
1, 22, 23 are rod-shaped ferrite cores 21a,
Windings 21b, 22b, 22a, 23a, respectively
23b, one end of which is connected to the ground potential, and the other end connected to the output terminal of the high frequency oscillator 4 via resistors 3, 3, 3.

Each of the detection coils 21, 22, 23 has one end surface of each ferrite core 21a, 22a, 23a facing a protective plate (not shown) of the probe 1 made of a non-magnetic material. The detection coils 21, 22, and 23 are arranged so that the directions in which they are arranged in parallel coincide with each other.

The oscillator 4 emits an output with a frequency of about 100KHz to 10MHz, and the detection coils 21 and 2
A high frequency current is passed through the windings 21b, 22b, and 23b.

Non-grounded terminals of each detection coil 21, 22, 23 are connected to differential amplifiers 5a, 5b. That is, the terminal of the winding 21b of the detection coil 21 is connected to the +input terminal of the differential amplifier 5a, and the terminal of the winding 22b of the detection coil 22 is connected to the -input terminal of the differential amplifier 5a and the +input terminal of the differential amplifier 5b. Furthermore, the terminals of the winding 23b of the detection coil 23 are respectively connected to the - input terminal of the differential amplifier 5b. Therefore, a signal corresponding to the difference between the terminal voltages of the detection coils 21 and 22 is obtained at the output terminal of the differential amplifier 5a.
On the other hand, the output terminal of the differential amplifier 5b is connected to the detection coil 2.
A signal corresponding to the difference between the terminal voltages of 2 and 23 is obtained.

The output signals of differential amplifiers 5a and 5b are provided to phase detection circuits 6a and 6b, respectively. The output of the oscillator 4 is given to these phase detection circuits 6a and 6b as a synchronizing signal.

The phase detection circuits 6a and 6b detect differential amplifiers 5a and 5 in the same phase according to the input signal from the oscillator 4.
The component of the b output is output, and this output is sent to the amplifier 7a,
7b and amplified to the required level.

The outputs of amplifiers 7a and 7b are both applied to an adder circuit 8 and a subtracter circuit 9. Adder circuit 8 is amplifier 7
A and 7b outputs are added and a sum signal PS is output.
The subtraction circuit 9 calculates the difference between the outputs of the amplifiers 7a and 7b and outputs the difference signal MS.

As will be described later, the sum signal PS is used to detect when the edge of the metal plate A approaches the probe 1, and the difference signal MS is used to detect when the edge of the metal plate A approaches the probe 1, for example.
That is, the metal plate A with the center of the detection coil 22 as a reference
It is used as a signal containing edge position information.

Next, the operation of this circuit will be explained. First, metal plate A
is located away from the probe 1, the voltages at the non-grounded terminals of the detection coils 21, 22, and 23 are equal, so the output signals of the differential amplifiers 5a and 5b are zero, and the sum signal PS and the difference signal MS is zero in both cases. Next, the metal plate A is connected to the detection coil 2 as shown in the figure.
The operation when moving from the 3 side to the detection coil 21 side will be explained. Now, as shown in FIG. 2, when the edge of the metal plate A is facing the detection coil 23, the eddy current generated in the metal plate A is due to the high frequency flowing through the detection coil 23. Since the impedance of the detection coil 23 is lower than that of the detection coil 22, the terminal voltage of the winding 23b of the detection coil 23 is lower than the terminal voltage of the winding 22b of the detection coil 22. The voltage signal corresponding to the difference is sent to the differential amplifier 5.
b output.

In FIG. 3, the horizontal axis represents the distance x from the center of the detection coil 22 to the edge of the metal plate A (positive on the detection coil 21 side), and the vertical axis represents the output voltages of the amplifiers 7a, 7b. 7b shows the relationship between the output of 7b and x. As shown in the figure, as the metal plate A approaches the detection coil 23 from a distance, the amplifier 7b
The output increases and reaches a maximum value when the edge of the metal plate A passes through the center of the detection coils 23 and 22, and as it approaches the detection coil 22, the output of the amplifier 7b decreases. As the edge of the metal plate A moves away from the detection coil 21 side, the output of the amplifier 7b approaches zero.

The same phenomenon occurs with the combination of the detection coil 22 and the detection coil 21, and the output of the amplifier 7a increases as the edge of the metal plate A approaches the detection coil 22, and the edge of the metal plate A approaches the detection coil 2.
The output of the amplifier 7a reaches its maximum value at the timing when it passes through the center of the coil 21, and decreases as it moves away from the detection coil 21.

FIG. 4 is a graph showing the relationship between the output of the addition circuit 8, that is, the sum signal PS, the output of the subtraction circuit 9, that is, the difference signal MS, and the distance x from the center of the detection coil 22 to the edge of the metal plate A. Since the adder circuit 8 adds the outputs of the amplifiers 7a and 7b shown in FIG. 3, the sum signal PS gradually rises from the point approaching the detection coil 23 on the edge side of the metal plate A as shown in the figure, and eventually becomes The output is approximately uniform until it passes through the detection coil 21, and the output gradually decreases as the edge of the metal plate A moves away from the detection coil 21.

On the other hand, since the difference signal MS is the difference between the outputs of the amplifiers 7a and 7b, it becomes a signal whose polarity is inverted at x=0 as shown in FIG. Therefore, the sum signal
PS is probe 1 or 3 detection coils 21, 2
This signal is effective as a signal for detecting that the edge of the metal plate A approaches the wide detection area covered by the metal plate A.

On the other hand, the difference signal MS has a steep change state, so it is effective for detecting the value of x from the signal level. In particular, the detection accuracy of x in the range between positive and negative peaks is Since the voltage change with respect to the change in range distance x is large, high accuracy is achieved.

In FIG. 3, the signals indicated by broken lines indicate the outputs of the amplifiers 7a and 7b, respectively, when the distance d between the metal plate A and the probe 1 becomes greater than the signal indicated by the solid line.

The broken line in FIG. 4 represents the amplifier 7 shown in broken line in FIG.
Sum signal PS and difference signal MS corresponding to a and 7b outputs
are shown respectively. As can be understood from this figure, the voltage value of the difference signal MS becomes zero when x=0 regardless of the distance d between probe 1 and metal plate A, so the edge of metal plate A It is possible to accurately detect the point in time when the center position of the detection coil 22 is reached, regardless of the distance d.
Also, since the sum signal PS is a signal that changes slowly,
If the threshold value of the subsequent comparing circuit (not shown) to which this sum signal PS is to be applied is appropriately selected, the approach can be accurately detected without being affected by the distance d.

The impedance of the detection coils 21, 22, and 23 is not affected by water, oil, etc. attached to the protective plate of the probe 1 or the surface of the metal plate A, so the edge of the metal plate A can be detected without being affected by the surrounding atmosphere. Of course, it is possible to detect the edges of the metal plate A in exactly the same way underwater or in oil.

The metal plate A to be detected is connected to each detection coil 2.
1, 22, and 23 that generate eddy currents on their surfaces by high-frequency current flowing therethrough, ie, a conductor, there is no need to provide a magnetic body, and there are few restrictions on the use.

In the above embodiment, the case where three detection coils are used has been explained, but if four or more detection coils are installed in parallel, a differential amplifier, a phase detection circuit, an amplifier, an addition circuit, and a subtraction circuit can be installed next to each other. It may be configured such that one is provided for every two detection coils. In addition, each detection coil is not limited to a configuration in which it is arranged in a straight line;
For example, they may be arranged in an arc shape. Furthermore, if only one of the sum signal PS or difference signal MS is required, one of the subtraction circuit 9 and the addition circuit 8 can be omitted.

As described above, the edge detection device for a metal body according to the present invention is a device for detecting the edge of a conductive metal body, and includes three or more detection coils arranged in parallel to face the metal body, and each detection coil arranged in parallel to face the metal body. an oscillator that causes a high-frequency current to flow through the coil; a plurality of differential voltage detection circuits that detect the difference between the terminal voltages of the two detection coils; and a plurality of phase detection circuits that phase-detect the output of the differential voltage detection circuit; The device is equipped with an addition circuit and/or a subtraction circuit for the outputs of the phase detection circuits, and is designed to detect edges of a metal body by the outputs of the addition circuit and/or subtraction circuit. , stable and highly accurate edge detection is always possible regardless of the surface condition of the detection unit and the detection target, whether in air, water, oil, etc., and there is no need to install a magnetic body on the detection target. etc. The present invention has excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the device of the present invention, FIG. 2 is a schematic diagram for explaining its operation, and FIG.
The figure is a graph showing the relationship between amplifier output and distance x,
FIG. 4 is a graph showing the relationship between the sum signal, the difference signal, and the distance x. 1... Probe, 4... Transmitter, 5a, 5b...
... Differential amplifier, 6a, 6b ... Phase detection circuit, 7
a, 7b...Amplifier, 8...Addition circuit, 9...Subtraction circuit, 21, 22, 23...Detection coil.

Claims (1)

[Claims] 1. A device for detecting the edge of a conductive metal body, comprising three or more detection coils arranged in parallel so as to face the metal body, an oscillator that causes a high-frequency current to flow through each detection coil, and two detection coils. A plurality of differential voltage detection circuits that detect differences in terminal voltages of respective detection coils, a plurality of phase detection circuits that phase detect the output of the differential voltage detection circuits, and an addition circuit and/or subtraction circuit for the outputs of the two phase detection circuits. 1. A device for detecting an edge of a metal body, comprising: a circuit for detecting an edge of a metal body using the output of the addition circuit and/or the subtraction circuit.