JPH0619103Y2 - Metal detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field of the Present Invention> The present invention relates to a metal detector used for detecting a metal contained in an article being conveyed.

<Prior Art> (Fig. 6) A metal detector has been conventionally used to detect a metal piece mixed in a product, particularly a plant product, during the transportation of the product.

FIG. 6 is a schematic diagram of a conventional metal detector used for such a purpose.

In the figure, reference numeral 1 is a conveyor, and the inspection object W is
Another conveyor or the like (not shown) is carried in from one end side 1a of the transfer conveyor 1, passes through the detection unit 2 provided in the central portion of the transfer conveyor 1, and another conveyor or the like (not shown) from the other end side 1b. Be shipped to.

The detection unit 2 is formed in a frame shape for passing an inspection object, generates a magnetic field in the frame from an internal transmission coil (not shown), and receives a change in the magnetic field in the frame as a reception coil (not shown). The object to be inspected W containing metal, which is configured to be detected by
When the magnetic field passes through the detecting section 2, the magnetic field changes, and the induced voltage in the receiving coil changes.
The presence or absence of metal in the object W to be inspected is detected.

The conveyor 1 is always driven in a fixed direction by a driving device 4 composed of a motor or the like, and
Also, the discriminating unit 3 is always operating with respect to the inspected object W sequentially conveyed, and when metal is mixed in the inspected object W, the drive is stopped by a signal from the discriminating section 3, This signal is output to the outside to select the object to be inspected.

However, such a metal detector must be able to detect a slight change in magnetic field due to a small metal mixed in the object W to be inspected.

For this reason, the detection unit 2 is, for example, Japanese Patent Laid-Open No. 59-24.
As disclosed in Japanese Patent No. 282, a pair of receiving coils are arranged along the transport direction of a device under test, and a differential component of a signal induced in two receiving coils is detected by a detection signal indicating a change in magnetic field. A high-sensitivity output is used, and the determination unit 3 determines the detection signal with high sensitivity.

Problems to be Solved by the Present Invention> However, in the conventional metal detector in which the high-sensitivity detection unit 2 and the determination unit 3 are always operated as described above, the transport conveyor 1 and the detection unit 2 are used. There was a problem that the same operation as that in which metal was mixed was caused by a slight impact or vibration with respect to.

As a technique for solving this, for example, Japanese Patent Publication No. 40-
No. 16872 discloses a metal object detection method in which a metal is detected after optically detecting that a product has reached a fixed position in front of a detection coil for metal detection.

In this detection method, the quality of the product is judged by whether or not the metal soup bag is detected by the detection coil with a very slight time delay after the product reaches a fixed position before the detection coil.

However, in such a method of determining the presence or absence of metal depending on whether or not metal is detected within a certain set time from the timing when the product comes to a fixed position, the product conveyance speed, conveyance posture, product length However, there is an inconvenience that the set time has to be changed depending on the position of the metal object in the product, and it is completely impossible to inspect different kinds of products in any order.

Further, as a technique related to a technique for inspecting an article while transferring it, Japanese Patent Application No. 58-171111 discloses an ultrasonic sensor for detecting the edge of a container (bin) being transferred and the contents in the container. Place the light emitter / receiver for determining the presence or absence of an object at the same position in the transport direction of the container, and between the time when the front end of the container passes and the time when the rear end passes in front of the ultrasonic sensor. , A method of detecting the presence or absence of contents is shown.

However, this detection method can be applied only when the target portion of the inspection is in a fixed position in the body to be inspected,
Not applicable for metal detection. That is, even if one sensor for detecting the passage of the object to be inspected is provided at a fixed position in the magnetic field, while the passage of the object to be inspected is being detected by the sensor, it is not always possible that the metal mixed in the object to be inspected. Does not always give the largest change to the magnetic field.

In particular, as described above, the 1
In the detection unit that detects the differential component of the pair of receiving coils, when the object to be inspected, which is shorter than the length of the magnetic field region, reaches the center of the magnetic field (that is, the intermediate portion between the two receiving coils), the object to be inspected Since the influence of the mixed metal of the body is generated in both reception coils by almost the same amount, the detection signal due to the mixed metal is hardly obtained.

The present invention solves this problem, and provides a metal detector capable of detecting metal with respect to various inspected objects with high sensitivity and resistance to disturbance without being influenced by the length of the inspected object or the transportation speed. It is intended to be provided.

<Means for Solving the Problems> In order to solve the problems, the metal detector of the present invention generates a magnetic field in a passage hole for passing an object to be inspected and passes the object to be inspected. A detection unit that receives the magnetic field with a pair of receiving coils arranged in a direction and outputs an operation signal of the pair of receiving coils as a detection signal according to a change in the magnetic field; and an object to be inspected in a passage hole of the detection unit. In a metal detector equipped with a conveyer for passing through and a discriminating unit which receives a detection signal from the detecting unit and discriminates the presence or absence of mixed metal in the inspection object passing through the detecting unit, with respect to the discriminating unit Judgment stop means for stopping the input of the detection signal or the judgment operation of the judgment section, and the tip of the inspection object conveyed by the conveyance conveyor reaches a position a predetermined distance before the entrance of the passage hole of the detection section. A first position detecting device for optically detecting that the rear end of the object to be inspected, which is conveyed by the conveyer, has reached a position where a predetermined distance has exited from the exit of the passage hole of the detector. A second position detecting device for optically detecting that the front end of the inspected object is detected by the first position detecting device and then the rear end of the inspected object is detected by the second position detecting device. Only until the determination is stopped, a detection control unit that cancels the stop of the input of the detection signal or the stop of the determination operation of the determination unit by the determination stop unit and determines the presence or absence of the mixed metal of the inspection object. It has.

<Operation> With this configuration, in the metal detector of the present invention, the first position detecting device detects the front end of the object to be inspected conveyed by the transfer conveyor, and the rear end thereof detects the second position detecting device. The presence or absence of mixed metal is detected by the detection signal from the detection unit only until the inspection object is detected, that is, from just before the inspection object enters the passage hole of the detection unit until it completely exits from the passage hole. When the object to be inspected is in front of the first position detecting device or behind the second position detecting device, the presence or absence of metal is not determined.

<Embodiment of the Invention> (FIGS. 1 to 4) Hereinafter, one embodiment of the invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing a metal detector of one embodiment, and FIG. 2 is a front view of FIG.

In the figure, 11 is a base portion of the metal detector 10, which is formed in a prismatic shape and arranged in parallel with each other.
Legs 11a are provided on both ends of each in a protruding manner.

Reference numeral 12 denotes a base portion supported by two base portions 11 so as to sandwich the front and rear lower end portions thereof.
Supporting plates 13 and 14 are attached to the upper portions of the a and the rear side 12b so as to be widened upward.

At the upper ends of the support plates 13 and 14, support portions 15 and 16 which are horizontally bent forward and backward are formed, respectively.

A conveyor 20 is arranged above the supporting portions 15 and 16.

Both ends 20a and 20b of the conveyor 20 are L-shaped attachment members 23 that support the conveyor rollers 21 and 22 on both sides.
Through both ends 15a, 15b of the supporting portions 15, 16,
It is attached to 16a and 16b.

One of the side surfaces 1 of the base 12 is provided on one of the conveying rollers 22.
Rotational force from a driving device (comprising a motor and a speed change mechanism) 25 attached to 2c is applied to the pulley 26 and the driving belt 2
7 is transmitted.

A detection unit 30 is installed at the center of the support units 15 and 16 so as to be orthogonal to the transport conveyor 20.

The detection unit 30 is formed in a frame shape, and is provided with a rectangular detection passage hole 31 in the center for passing the conveyor 20 and an article conveyed by the conveyor 20.

Further, on both sides of the detection unit 30, first and second light emitting and receiving devices 33 having an optical axis that traverses the transport path of the transport conveyor 20,
34 is provided on the supporting portions 15 and 16.

The first light projecting / receiving device 33 constitutes the first position detecting device of this embodiment, and the detection passage hole 3 of the detecting section 30.
1, a light projecting unit 33a that outputs light that crosses a position a predetermined distance before the entrance, and a light receiving unit 33b that receives this light (first
(Not shown in FIGS. 2 and 3), the second light projecting / receiving device 34 constitutes the second position detecting device of this embodiment, and the detection passage hole of the detecting portion 30 is provided. Projection unit 3 that outputs light that crosses a position behind a predetermined distance from the exit of 31
4a and a light receiving portion 34b for receiving this light.

The first and second light projecting / receiving devices 33, 34 include a light projecting unit 33a,
It is formed so that the output level of the light receiving portions 33b and 34b becomes "H" when the light from 34a is shielded by the inspection object.

A control unit 35 is attached to the upper portion of the detection unit 30.

FIG. 3 shows the detection unit 30 and the first and second light projecting / receiving devices 3.
3 is a diagram showing a circuit configuration of the control unit 35 and 34;

In FIG. 3, in the detection unit 30, a transmission coil L1 for generating a magnetic field in the detection passage hole 31 and a pair of reception coils arranged opposite to the transmission coil L1 and arranged side by side in the passage direction of the object to be inspected. L2 and L3 are stored. The two receiving coils L2 and L3 are differentially connected to each other.

The transmitter coil L1 generates an equal amount of alternating magnetic flux with respect to the receiver coils L2 and L3 by an oscillator OSC that generates an AC signal having a predetermined frequency.

The output sides of the receiving coils L2 and L3 are differentially connected via a variable resistor VR, and the central terminal of this variable resistor VR is a switch 48 (discrimination stopping means) which is opened and closed by a detection control unit 45 described later. Is connected to the amplifier 37 of the discriminator 36.

The variable resistor VR is used to balance the induced voltage by finely adjusting automatically or manually when different induced voltages are generated in the receiving coils L2 and L3 due to the influence of the ambient temperature or the like. is there.

The output of the amplifier 37 is input to the detection unit 38.

The detection unit 38 is configured to synchronously detect the signal from the amplifier 37 by the oscillation signal of the oscillator OSC, rectify the signal, and output the detection signals obtained by A / D conversion.

The detection signal from the detector 38 is input to the comparator 40.

The comparison unit 40 compares a predetermined reference value with the detection signal from the detection unit 38. When the detection signal is larger than the reference value, for example, the comparison unit 40 sends an "H" level stop signal to the alarm circuit 41 to mix the metal. And stop switch 4
2 is opened to stop the power supply to the drive device 25.

The stop signal from the comparison unit 40 is released by a manual reset switch (not shown) and becomes "L" level.

On the other hand, the light receiving portion 33 of each of the first and second light projecting / receiving devices 33, 34.
The received light signals from b and 34b are input to the detection control unit 45.

The detection control unit 45 controls the opening and closing of the switch 48 by the light receiving signals from the light receiving units 33b and 34b, and is configured, for example, as shown in FIG.

In FIG. 4, the output of the light receiving portion 33b is input to the set terminal S of the flip-flop 46, and the output of the light receiving portion 34b is input to the clock terminal CK of the flip-flop 46 via the inverter 47. The D terminal of the flip-flop 46 is fixed at "L" level.

Therefore, when the "H" level signal from the light receiving unit 33b is input, the output Q of the flip-flop 46 is set to the "H" level, and the light receiving signal from the light receiving unit 34b is "L".
When it falls to the level, the output Q becomes "L" level. The output Q of the flip-flop 46 at the initial operation is reset to the "L" level.

The output (output Q) of the detection control unit 45 drives the switch 48 provided on the input side of the determination unit 36 to open and close. That is, the switch 48 is opened when the output Q of the flip-flop 46 is at "H" level, and closed when the output Q of the flip-flop 46 is at "L" level, which cuts off the input of the detection signal to the discrimination unit 36 and is mixed. Stop the determination of the presence or absence of metal.

<Operation of the Embodiment> Next, the operation of the embodiment will be described.

When the operation is started, power is supplied to the drive device 25 via the stop switch 42, and the transport device 20 is driven by the drive device 25 from the one end side 20a to the other end side 20b. At this time, the flip-flop 46 of the detection control unit 45
Is reset, and its output Q becomes "L" level, so that the switch 48 is closed and the input of the determination unit 36 is short-circuited.

Here, the object W to be inspected is transferred from another conveyor or the like to the conveyor 2
When sequentially loaded into one end side 20a of 0, the object W to be inspected
Are conveyed toward the detection passage hole 31 of the detection unit 30.

When the tip of the object W to be inspected reaches the first light projecting / receiving device 33, the light receiving signal from the light receiving section 33b becomes "H" level at t1 as shown in FIG. 46 is set, and its output Q becomes "H" level as shown in FIG. 5 (c).

Therefore, the switch 48 is opened, and the detection signal from the detection unit 30 is input to the determination unit 36.

The rear end of the inspection object W passes through the first light projecting / receiving device 33 t
At 2 o'clock, the output of the light receiving unit 33b returns to the "L" level.

When the inspection object W enters the detection passage hole 31 of the detection unit 30,
The detection signal due to the change in the magnetic field is input to the determination unit 36 via the variable resistor VR and amplified and detected. The detected signal is compared with a predetermined reference value in the comparison unit 40.

Here, when a metal is mixed in the inspection object W,
A stop signal from the comparison unit 40 is sent to the alarm circuit 41 and the stop switch 42 to notify the metal mixing and the conveyor 20 stops. When the metal mixture is not detected, the inspection object W passes through the detection unit 30 as it is.

When the tip of the inspection object W that has passed through the detection unit 30 is the second at t3.
When the light receiving signal from the light receiving unit 34b reaches the "H" level as shown in FIG. 5 (b), the trailing end of the light receiving / receiving device 34 passes through the second light emitting / receiving device 34 at "t4". Return to L "level.

Therefore, at the time t4, the output Q of the flip-flop 46 of the detection control unit 45 changes from "H" level to "L" level as shown in FIG.
Is closed, and the input of the detection signal from the detection unit 30 to the determination unit 36 is stopped.

As a result, the detection signal from the detection unit 30 takes time (t1) from the time when the tip of the object W to be inspected reaches the first light projecting / receiving device 33 to the time when its rear end passes through the second light projecting / receiving device 34. From the time t4), it is sent to the determination unit 36,
When the object W to be inspected is in another position, it is cut off.

Therefore, even if there is a shock, vibration, or the like on the transport conveyor 20 or the detection unit 30 during the time from t1 to t4, the malfunction does not occur.

In the same manner, the detection operation is performed on the inspected objects W sequentially carried in while receiving the signal interruption control from the detection control unit 45.

<Other Embodiments of the Present Invention> In the above embodiment, the detection control unit 45 is composed of individual elements such as flip-flops. It does not depart from the gist of the present invention to configure a microcomputer having a program.

Further, in the above embodiment, the detection signal from the detection unit 30 is short-circuited by the switch so that the metal detection operation is not performed. However, for example, the amplifier 37, the detection unit 38 or the comparison unit 40 of the discrimination unit 36 may be operated. A means for stopping the operation may be provided, and the detection control unit may control the stopping means to start or stop the metal detection operation.

<Effects of the Invention> As described above, in the metal detector of the invention, after the first position detection device detects that the tip of the object to be inspected has passed before the entrance of the passage hole of the detection portion. , The input of the detection signal from the detection unit to the determination unit is stopped or determined only until the second position detection device detects that the rear end of the inspected object has exited the exit of the passage hole by a predetermined distance. It is configured to release the stop of the discriminating operation of the portion and discriminate the presence or absence of the mixed metal.

For this reason, the presence or absence of the mixed metal is determined by the detection signal only while the inspected object influences the magnetic field of the detection unit, so that the malfunction does not occur even when the magnetic field changes due to disturbance or the like in another period. Absent. Further, since it is not necessary to set the time for determining the presence or absence of metal, even if the length, the transportation posture, and the transportation speed of the object to be inspected are different, it is possible to correspond without any change. Different varieties can also be inspected in any order.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention, FIG. 2 is a front view of FIG. 1, FIG. 3 is a block diagram showing a control part of the embodiment, and FIG. FIG. 5 is a circuit diagram showing the main part of FIG. 5, FIG. 5 is a signal diagram showing the operation of the main part, and FIG. 6 is a schematic view of a conventional device. 10 ... Metal detector, 20 ... Conveyor, 30 ...
Detection unit, 31 ... Detection passage hole, 33 ... First light emitting / receiving device, 34 ... Second light emitting / receiving device, 35 ... Control unit, 36
...... Discrimination unit, 45 ...... Detection control unit, 48 ...... Switch,
L1 ... Transmission coil, L2, L3 ... Reception coil.

Claims (1)

[Scope of utility model registration request] 1. A magnetic field is generated in a passage hole for passing an object to be inspected, and the magnetic field is received by a pair of receiving coils lined up in the passing direction of the object to be inspected. A detection unit that outputs a signal as a detection signal corresponding to the change in the magnetic field, a conveyor that passes the inspection object through a passage hole of the detection unit, and a detection signal from the detection unit, and the detection unit In a metal detector provided with a discriminating unit for discriminating the presence or absence of mixed metal of an inspected body passing therethrough, a judgment stopping unit for stopping the input of the detection signal to the judging unit or the judging operation of the judging unit; A first position detection device that optically detects that the tip of the inspection object conveyed by the conveyor has reached a position a predetermined distance before from the entrance of the passage hole of the detection unit; A second position detecting device for optically detecting that the rear end of the sent inspection object has reached a position where the rear end of the inspection part has exited from the exit of the passage hole by a predetermined distance; Only after the detection by the first position detecting device until the rear end of the inspected object is detected by the second position detecting device, the input of the detection signal by the determination stop means or the determination is stopped. A metal detector, comprising: a detection control unit that releases the stop of the discriminating operation of the unit and discriminates the presence or absence of mixed metal in the inspection object.