JPS6071415A - Detecting device for longitudinal crackon belt - Google Patents

Abstract

PURPOSE:To prevent longitudinal cracks on a belt from being erroneously detected at a position where no loop coil is buried by providing a phase rotating circuit in the captioned device in which the longitudinal cracks is are detected by an output of a detecting coil electromagnetically coupled with the loop coil curried in a conveyor belt along its width. CONSTITUTION:The captioned device includes a detection coil 24 disposed in a confronting relation to a belt 10 so as to be electromagnetically coupled with plural loop coils 14 extending in the width direction of the belt 10 and buried in an equidistant interval. When a constant amplitude AC current is supplied to the aforesaid detecting coil 24 from a constant-current circuit 28, constant and varying fractions of voltage appear at both ends of the coil 24. Here, in order to remove the constant fraction described above, a voltage corresponding thereto is generated from a cancellation voltage generating circuit 34, and applied to a cancelleration circuit 36. In addition, only the aforesaid varying fraction is taken out, amplified 38, phase-detected by detectors 40, 42, and the resultant resistance and clearance variation components are outputted. Phase rotation is effected by a phase rotation circuit 44 based on both variation components.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention is a method for automatically detecting longitudinal tears that occur during operation of a conveyor belt used for transporting ore, lime, coal, etc. without contacting the belt. related to a device for

Conventional technology and problems Conveyor belts that transport ore, lime, coal, etc. may be struck by the sharp edges of stones, etc., resulting in vertical cracks. Tears develop throughout the length of the belt, not only impairing the conveying function of the conveyor, but also rendering the entire belt unusable. Therefore, it is desirable to detect and repair vertical tears as soon as possible, but it is impossible to constantly monitor vertical tears with the naked eye in belts that are several hundred meters or more in length. . Therefore, there is a need for a device that automatically detects vertical tears in conveyor belts, and various devices have been developed and devised in the past.

As a typical example, as described in Japanese Utility Model Publication No. 44-4180, a loop coil is buried in a belt, a detection coil is placed directly above the passage of the belt, and the effective inductance between the terminals of this detection coil is There are devices that detect changes in Methods for detecting this change in effective inductance L include a method in which the detection coil is inserted into one side of the bridge and the corresponding change is extracted as unbalance of the bridge, and a method in which the detection coil is used as an inductor coil of an oscillation circuit. There is a method of extracting the change in the oscillation frequency as a change in the oscillation frequency.

However, when this method is applied to a conveyor belt in which reinforcing steel cords are embedded, when the distance between the detection coil and the belt changes, the effective inductance also changes and an erroneous signal is generated.

In general, conveyor belts frequently experience vertical vibrations and lateral vibrations during operation, and therefore, the conventional method described above, as long as it is applicable to conveyor belts with embedded reinforcing steel cords, does not generate many false signals. Therefore, it cannot be put to practical use. Furthermore, even if the distance between the detection coil and the belt can be effectively kept constant using a copying roll device, etc., the effective inductance at the connection portion of the steel cords will be reduced due to the difference in the embedded density of the steel cords. changes, causing an erroneous signal to be emitted.

OBJECTS OF THE INVENTION The present invention provides a method to detect vertical tearing of a conveyor belt, particularly a conveyor belt in which reinforcing steel cords are buried, without malfunction during the service life of the belt, and to automatically generate an alarm. This is what we are trying to do.

Structure of the Invention The present invention provides an apparatus for detecting longitudinal tearing of a conveyor belt, which includes a plurality of loop coils extending in the width direction of the belt and embedded at predetermined intervals in the longitudinal direction of the belt, and a device for electromagnetically coupling with the loop coils. a detection coil arranged opposite to the belt; a circuit connected to the detection coil to detect changes in effective reactance and effective resistance of the coil; and a circuit connected to the circuit to detect changes in effective reactance and resistance of the coil; This feature includes a circuit that rotates the phase so that the impedance change characteristic when facing a part other than the normal loop coil coincides with the actance axis, which will be explained in detail with reference to the drawings below. .

Embodiment of the Invention FIG. 1 shows a conveyor belt equipped with a reinforcing steel cord and a loop coil for detecting longitudinal cracks, 10 the belt made of rubber, 12 the steel cord, 14
is the loop coil. +a) is a schematic plan view, (bl
is the same cross-sectional view, and as shown in the cross-sectional view (bl), the steel cord 12 and the route coil 14 are buried in different layers, the former being on the front side of the belt on which loads such as ore are placed, and the latter on the back side of the belt. Placed on the side.Steel cord 12
extend linearly in the longitudinal direction of the belt, and are arranged in plural at approximately equal intervals in the belt width direction. The loop coil 14 is a one-turn or multiple-turn short-circuit coil, and the winding axis is oriented perpendicular to the belt surface, and the rectangular coil extends across the entire width of the belt. In Figure 1, the loop coil 14
Although only one is shown, in reality, many are buried at a predetermined pitch (for example, 30 m) in the belt length direction. The reinforcing steel cord 12 and the loop coils 1 and 4 are electrically insulated.

FIG. 2 shows a state in which the baggage 16 is conveyed by the belt conveyor 10. 18.20 is a pulley. 22
is the detection end, which is equipped with a detection coil, this detection coil is the primary winding of the transformer, and the loop coil is the secondary winding of the transformer.
It is detected as a change in the impedance of the detection coil (a change in a vector consisting of an effective resistance component R and an effective reactance component X).

If a change in the impedance of the detection coil is detected as a change in the magnitude and/or direction of a vector consisting of an R component and an X component, it is possible to accurately detect loop coil breakage and hence vertical belt tearing. That is, when the detection coil faces the part A where the loop coil of the belt is buried;
When facing the portion B where only the reinforcing steel cord is buried, a clearly different vector change appears. Furthermore, if the loop coil is disconnected, the vector at that time will be almost the same as the vector of portion B.

FIG. 4 shows impedance changes of the detection coil measured by specifying the measurement frequency and the dimensions of the loop coil and steel cord. The vertical axis shows the beam actance change ΔX, the horizontal axis shows the resistance change ΔR, and vI to v5 are the impedance changes of the detection coil measured at the loop coil section. vl
is when the distance between the detection coil and the belt is 60-, v2 is when the fin is 50, v3 is when the crane is 40, and v2 is 30 when the fin is the same.
In the case of the fin, when vl is the same 20 mm, a larger change in impedance is observed as the interval becomes smaller.

The distance between the detection coil and the belt is related to the magnitude of the vectors, but is not related to the phase angle (orientation), and these vectors Vl, V2 . ... is on the straight line C1. Straight line C2 shows the impedance change when the detection coil faces only the reinforcing steel cord of the belt, and straight line C] shows the impedance change when the detection coil faces the broken loop coil, which is clear from the figure. These are almost the same, and are clearly different from that of the normal loop coil section C1. Similarly, if the distance between the detection coil and the belt differs, the magnitude of the vector changes, but the phase angle remains the same. The dotted lines are Vl and V on C2 and C3
2. ...Indicates the corresponding position.

Therefore, if each vector is rotated all at once so that the straight line C2 is two times the Δχ axis, it can be said that when the ΔR acid component appears, it is when the detection coil is opposed to the normal loop coil. The distance between the ΔR acid component detection coil and the belt varies somewhat (between V+ and ■5), but it is necessary to set an appropriate threshold value depending on the possible interval and judge whether or not a ΔR greater than that is detected. For example, the change in the interval is negligible.

As shown in FIG. 3, the reinforcing steel cords of the belt are engaged over a predetermined length at the connecting portion C, and the embedding density is high. Therefore, when detecting the effective inductance directly, there is a risk of erroneous detection in this part, but with the present invention, which treats the vector as a vector, there is no such erroneous detection. In other words, the impedance of the detection coil in this connecting portion C is also the same as the straight line C in Fig. 4.
2, and there is almost no change in phase angle except for a slight increase in size. Therefore, if the above phase rotation is performed, no ΔR acid component is generated at the connecting portion C, and no signal is generated.

FIG. 5 shows an embodiment of the invention □' open circuit. 24 is the above detection coil, 26 is an AC power supply, 28 is a constant current circuit for driving the detection coil 24 with a constant current, 30 is a high input impedance buffer, 32 is a reference signal 31. It is a phase sick that generates S2. Further, 34 is a circuit for generating a cancellation voltage for the cancellation circuit 36, 38 is an amplifier, 40.42 is a phase detector, and 44 is a phase rotation circuit.

When an alternating current I of constant amplitude is supplied to the detection coil 24 by the constant current circuit 28, a voltage ■ proportional to the impedance Z of the coil appears across the coil 240 (V=I
At Z! = constant).

Since this voltage consists of a fixed component and a varying component, the fixed component is generated in a circuit 34, this is added to a circuit 36, the fixed component is removed in this circuit, and only the varying component is taken out and this is amplified by an amplifier 38. do. This is to avoid saturation of the amplifier 38 if the fixed portion is included in the amplification. The phase of the amplified voltage change is detected by a detector 40, 42 which can apply reference voltages si' and s2 having a phase difference of 90°, and a resistance change ΔR and a reactance change ΔX are output. These .DELTA.R9.DELTA.X are added to the phase rotation circuit 44 to perform processing to align the aforementioned straight line C2 with the .DELTA..chi. axis. Of ΔX and ΔR that have been subjected to such processing, ΔR or it is checked with a threshold value vth, and a signal equal to or greater than the threshold value vth is taken out as an output signal ΔR'. This is a signal indicating normal loop coil detection as described above.

FIG. 6 shows another embodiment of the invention. 46 is a floating transformer whose primary winding is connected to the above-mentioned AC power supply 26, and whose secondary winding is the detection coil 24 and the dummy coil 4B.
, energizes the bridge 54 consisting of resistors 50, 52. Each side of this bridge 54 is adjusted so that it is balanced when the detection coil 24 faces the non-loop coil portion of the belt, and the input end of the amplifier 38 is connected to the detection end of this bridge to generate a bridge unbalance voltage. Try to amplify it.

As can be easily inferred from the above explanation, this bridge 5
4 becomes unbalanced only when the detection coil 24 faces the normal loop coil 14, and the unbalanced voltage includes only the variation and does not include the fixed voltage, so the canceling circuit 36 etc. in Fig. 5 is unnecessary. It is.

The components after the amplifier 38 are the same as those shown in FIG.

According to this circuit, disconnection of the loop coil and, therefore, longitudinal tearing of the belt can be detected reliably. Note that the detection output of this detection circuit is that when the loop coil is disconnected, the event pulse ΔR' indicating the presence of the loop coil is no longer generated, so this alone is not sufficient to generate a vertical tear alarm, for example, when the loop coil is disconnected. It is necessary to issue a loop coil breakage or vertical belt tear alarm on the condition that there is no event pulse even if this pulse occurs. However, such means can be constructed as appropriate and any known means can be used. For example, a disc provided with a light transmission hole is connected to a belt drive pulley, and when the detection coil faces a loop coil on the belt, light passes through the light transmission hole and enters the light receiving element. The output is the loop coil detection output, which is added to one input of the AND gate, and the other input is the output ΔR of the circuit 44.
An example of this is to add an inverted signal of .

If the belt is stretched and slack, it may be misaligned when detected by the disc described above, but in order to prevent this, a one-shot multi or similar device is activated to create a pulse of an appropriate width (window pulse), and this is used as an AND gate. This can be handled by opening the input gate over an appropriate width before and after the expected position of the loop coil. It is also possible to directly detect the position of the loop coil by embedding a magnet in the belt at or near the loop coil position and detecting this with a second detection coil.

When the loop coil 14 makes electrical contact with the steel cord 12, the impedance of the detection coil changes randomly. Therefore, it is better to insulate both.

In addition, the loop coil 14 is preferably laid on the belt 10 so as to directly face the detection coil 24, and when the steel cord 12 is inserted between them, the steel cord performs an electromagnetic shielding function, and the loop coil detection output is reduced. Become.

As described in detail, according to the present invention, it is possible to reliably detect vertical tearing of a belt conveyor with a built-in steel cord, and it is extremely effective. Of course, the present invention may be applied to a belt conveyor that does not have a built-in steel cord, and no problem will occur even if this is done.

[Brief explanation of the drawing]

1 to 3 are explanatory diagrams of a conveyor belt, FIG. 4 is an impedance change characteristic diagram of a detection coil, and FIGS. 5 and 6 are block diagrams showing an embodiment of the present invention. In the drawing, 10 is a conveyor belt, 12 is a steel cord, 14 is a loop coil, 24 is an &output coil, 30, 36
．． 3B, 40.42 or 54°3B, 40.42 is Δ
The R1ΔX detection circuit 44 is a phase rotation circuit.

Claims (1)

[Claims] A device for detecting longitudinal tearing of a conveyor belt, comprising: a plurality of loop coils extending in the width direction of the belt and embedded at predetermined intervals in the longitudinal direction of the belt; a detection coil arranged to face the belt; a circuit connected to the detection coil to detect changes in effective reactance and effective resistance of the coil; A device for detecting longitudinal belt cracks, comprising: a circuit that rotates the phase so that the impedance change characteristic when facing a part other than the coil matches the reactance axis.