JPH06249605A - Method and device for detecting traveling object - Google Patents

Abstract

PURPOSE:To make a traveling object detecting device which detects whether or not a traveling object which is the object to be detected of the detecting device is at a specific position from a magnetic field caused by the traveling object not to make any malfunction even when a strong external magnetic field is impressed upon the detecting device from a welding machine, etc., without increasing the size or weight of the detecting device. CONSTITUTION:At least two magnetic sensors 11 and 12 which can detect a magnetic field produced by a magnet MG mounted on a piston 3 are arranged at an interval along the moving direction of the piston 3 and, when the sensors 11 and 12 detect the magnetic field with a time lag which is equal to or longer than a prescribed period of time, the title detecting device 5 detects that the piston 3 is in a specific position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for detecting whether or not a moving object to be detected is at a specific position by a magnetic field emitted from the moving object.

[0002]

2. Description of the Related Art Conventionally, in order to detect a piston position of a fluid pressure cylinder, a detection device having a magnetic sensor which operates by a magnetic field emitted from a magnet mounted on the piston has been used. Such a detection device is attached to the surface of the cylinder tube, and when the piston comes to the attachment position, the magnetic sensor turns on and outputs a detection signal.

However, since the magnetic sensor built in the detection device may be activated by an external magnetic field unrelated to the piston, for example, from a welding machine, there is no piston at the mounting position of the detection device. The strong magnetic field generated may turn on the magnetic sensor and output an incorrect detection signal.

Conventionally, in order to reduce such malfunction due to an external magnetic field, the following method has been adopted. The magnetic shield of the magnetic sensor is doubled or tripled to reduce the influence of the external magnetic field. By using a rare earth for the magnet attached to the piston, a strong magnetic field is generated, and the sensitivity of the magnetic sensor is lowered to reduce the influence of the external magnetic field.

[0005]

However, the above-mentioned detection method has the following problems. That is, the above-described method increases the size and weight of the detection device. In this method, since the price of the magnet becomes high, the detection device becomes expensive, and iron powder or the like adheres to the magnet and its vicinity, which easily causes a failure. In addition, in any of the detection methods (1) and (2), a malfunction may occur with respect to a strong magnetic field.

In view of the above-mentioned problems, the present invention provides a method and apparatus for detecting a moving object that does not become erroneous even with a strong external magnetic field generated by a welding machine or the like without increasing in size or weight. Has an aim.

[0007]

In order to solve the above-mentioned problems, a method according to the invention of claim 1 is for detecting whether or not the moving object is at a specific position by a magnetic field emitted from the moving object. In the method, at least two magnetic sensors capable of sensing a magnetic field emitted from the moving object are arranged at positions separated from each other along a moving direction of the moving object, and the two magnetic sensors are set to a predetermined distance from each other. Is a method for detecting a moving object, which detects that the moving object is at a specific position when a magnetic field is sensed at an interval longer than or equal to.

According to a second aspect of the present invention, the moving object is not located at a specific position when the two magnetic sensors cease to sense the magnetic field at intervals of a predetermined time or more. This is a method of detecting a moving object.

According to a second aspect of the present invention, there are provided two magnetic sensors arranged at positions distant from each other, means for measuring a time difference between signals output from the two magnetic sensors, and the time difference being preset. Compared with the reference time
And means for outputting a detection signal according to the comparison result.

[0010]

Since the two magnetic sensors are arranged at distant positions, there is a time lag in sensing a moving object by these two magnetic sensors. On the other hand, the external magnetic field is sensed by the two magnetic sensors almost at the same time or within a fixed time. Therefore, by measuring the sensing time of the two magnetic sensors and comparing the sensing time with the reference time, the moving object is detected. Is detected or an external magnetic field is detected, and a correct detection signal is output.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an example of the arrangement of two magnetic sensors 11 and 12 according to the detection method of the present invention, and FIG. 2 is an ON signal S1 and 2 of the two magnetic sensors 11 and 12 of FIG. FIG. 6 is a timing chart showing the relationship with the signal Sd.

In FIG. 1, the detection device 5 mounted on the surface of the tube 2 of the fluid pressure cylinder 1 has two magnetic sensors 11 and 12 (first magnetic sensor 11 and second magnetic sensor 11).
The magnetic sensors 12) are arranged at a distance L from each other. As such magnetic sensors 11 and 12, for example, a magnetic resistance element, a Hall element, a reed switch, or a combination of these with a detection circuit is used.

These magnetic sensors 11 and 12 are activated by the magnetic fields of the magnets MG mounted on the piston 3, which is a moving object, at their lower positions, and output ON signals.

Here, the piston 3 is the magnetic sensor 11,
If the position 12 (lower position) is passed from left to right at speed V, the magnetic sensor 11 first turns on,
After that, the magnetic sensor 12 is turned on. The time difference td when the magnetic sensors 11 and 12 are turned on (difference time td) is expressed by the following equation (1).

Td = L / V (1) As shown in the above equation (1), the time td is proportional to the distance L and inversely proportional to the speed V. Generally, the velocity V of the piston 3 is a finite value, so if the maximum value is Vm,
The time td is always a value equal to or longer than the time tm calculated by L / Vm. That is, the following expression (2) is always established.

Td ≧ tm (2) On the other hand, when the magnetic sensors 11 and 12 are turned on by an external magnetic field, for example, a strong magnetic field generated from a DC welding machine,
These may be turned on almost at the same time, and the time difference may be zero.

Therefore, the time (reference time) tm corresponding to the distance L and the maximum speed Vm is obtained in advance, the time difference td when the two magnetic sensors 11 and 12 are turned on is measured, and the measured time td is If it is longer than the reference time tm, it can be determined that the operation is normal due to the movement of the piston 3, not due to the external magnetic field.

That is, as shown in FIG. 2A, when the ON signals S1 and S2 are output in the order of the first magnetic sensor 11 and the second magnetic sensor 12, the output timing is deviated by the reference time tm or more. If there is a magnetic sensor 1
The regular detection signal S at the same timing as the ON signal S2 of 2
Output d. And the two magnetic sensors 11, 12
When the ON signals S1 and S2 are simultaneously output, the detection signal Sd is not output because the magnitude of the timing deviation is naturally less than the reference time tm.

Further, FIG. 2B shows each magnetic sensor 1
ON width of 1 and 12 is long, and two magnetic sensors 11 and 1
The case where the two ON states overlap is shown. Also in this case, since the timings at which the two magnetic sensors 11 and 12 are turned on deviate by the reference time tm or more, the detection signal Sd is output at the same timing as the on signal S2 of the magnetic sensor 12.

In the case of FIG. 2B, the ON signal S2 of the magnetic sensor 12 is passed after the reference time tm has elapsed since the ON signal S1 of the magnetic sensor 11 was turned OFF.
Is turned off, it is determined that the magnetic sensor 12 is turned off not by the external magnetic field but by the movement of the piston 3. Therefore, the detection signal Sd is turned off at the same time when the on signal S2 of the magnetic sensor 12 is turned off.

FIG. 2C shows two magnetic sensors 1.
When the ON states of 1 and 12 overlap, and the piston 3 stops at a position where both magnetic sensors 11 and 12 are turned on, then the piston 3 moves in the opposite direction and the magnetic sensors 11 and 12 are turned off. Is shown.
Such a state occurs, for example, when the detection device 5 is attached to the stroke end position of the piston 3.

Also in this case, since the timings at which the two magnetic sensors 11 and 12 are turned on deviate by the reference time tm or more, the detection signal Sd is output at the same timing as the on signal S2 of the magnetic sensor 12. While the two magnetic sensors 11 and 12 are on, the magnetic sensors 11 and 12 are simultaneously turned off by the external magnetic field, but they are turned off at the same time and there is no time difference. It is determined that the operation is not normal, and the detection signal Sd is not turned off. After that, since the magnetic sensor 12 is turned off and the magnetic sensor 11 is turned off after the elapse of the reference time tm or more, it is determined that the magnetic sensor 11 is turned off not by the external magnetic field but by the movement of the piston 3. Then, the detection signal Sd is turned off.

Thus, according to the detection method of the present invention,
By measuring a time difference td at which the two magnetic sensors 11 and 12 are turned on or off and comparing the time difference td with a reference time tm, the on operation or the off operation is a normal operation due to the movement of the piston 3, or an external operation. It is possible to easily and surely identify whether the malfunction is caused by the magnetic field, and it is possible to easily output only the normal detection signal Sd free from the malfunction caused by the external magnetic field. Further, as the structure of the detection device 5, the two magnetic sensors 11 and 12 may be arranged separately,
The configuration is simple, and the detection device 5 can be made compact.

An example of the numerical values is as follows. For example, the distance L is 20 mm and the speed Vm is 1000.
If it is mm / sec, the reference time tm is 20 msec, and if the time difference td is 20 msec or more, the normal detection signal Sd is output. However, as the reference time tm, the time obtained by increasing or decreasing the time obtained from the distance L and the maximum speed Vm in the positive or negative direction may be used. For example, in the above numerical example, 20 mse obtained
With respect to c, the reference time tm is set to 2 with a margin of 5 msec.
It may be 5 msec.

When the cause of the external magnetic field is the AC welding machine, the operation of the magnetic sensors 11 and 12 is 1 cycle (20 msec) due to the variation in the sensitivity of the magnetic sensors 11 and 12.
Or 17 msec) or there is a half cycle deviation, so the time of the deviation or the time with a margin may be used as the reference time tm. In the case of a DC welding machine, since the two magnetic sensors 11 and 12 operate almost at the same time,
An extremely short time (for example, several mse) in consideration of variations of the magnetic sensors 11 and 12 and timing error of the detection circuit.
(c to 10 msec) may be set as the reference time tm.

FIG. 3 is a block diagram showing an example of the circuit configuration of the detecting device 5a according to the present invention, and FIG. 4 is a timing diagram showing the signal states of the respective parts of the detecting device 5a. Detection device 5a
Is composed of two magnetic sensors 11a and 12a, waveform shaping circuits 13 and 14, a logic circuit 15, a time measuring circuit 16, a determination circuit 17, an output circuit 18, and a power-on circuit 19.

The magnetic sensors 11a and 12a are each composed of two magnetoresistive elements connected to a bridge together with two resistors, and are connected so that the output voltage changes according to the magnetic field.

The waveform shaping circuits 13 and 14 shape the voltage waveforms output from the magnetic sensors 11a and 12a, binarize the voltage waveforms at appropriate levels, and respectively form the magnetic sensors 11a and 12a.
It is converted into signals S1 and S2 which are turned on when 12a senses a magnetic field above a certain level.

The logic circuit 15 includes two magnetic sensors 11
3 based on the signals S1 and S2 input from a and 12a.
Two signals S3, 4, 5 are output. The signal S3 is a signal that turns on when both the magnetic sensors 11a and 12a turn on, and is obtained by taking the logical product of the signals S1 and S2. The signal S4 indicates that both magnetic sensors 11
The signals a and 12a are turned on when they are turned off, and are obtained by inverting the logical sum of the signals S1 and S2. The signal S5 is a signal that turns on when only one of the two magnetic sensors 11a and 12a turns on,
It is obtained by taking the exclusive OR of the signals S1 and S2.

The time measuring circuit 16 measures the time from the rising of the signal S5, rises after a preset reference time tm from the rising of the signal S5, and
3 or rising of signal S4 (falling of signal S5)
At the same time, it outputs a falling signal S6.

The decision circuit 17 receives the input signal S3,
Based on 4 and 6, the signal S7 corresponding to the detection signal Sd is output. Further, based on the signal S8 from the power-on circuit 19, the detection signal Sd for transitional treatment is output.

The output circuit 18 outputs a detection signal Sd which can be output to the outside based on the signal S7 and used for control. The power-on circuit 19 initializes the state of each part and outputs a signal S8 for outputting a correct detection signal Sd according to the state of the piston 3 (magnet MG) when the power of the detection device 5a is turned on. To do.

For example, when the detection device 5a is attached to the stroke end position of the piston 3, the piston 3 is often stopped at a position where the two magnetic sensors 11a and 12a are operated. When the power of the detection device 5a is turned on, the two magnetic sensors 1
Since there is no time difference between the turning on of 1a and 12a, the detection signal Sd is not output as it is. To correct this, when the power is turned on in such a state, the signal 8 is output so as to output the detection signal Sd.

In the detection device 5a shown in FIG. 3, the detection signal Sd is normally output regardless of which side of the magnetic sensors 11a, 12a the piston 3 approaches or departs from. Although the determination circuit 17 can be configured in the above, in order to simplify the configuration of the determination circuit 17, another magnetic sensor 11b may be provided at a position symmetrical to the magnetic sensor 11a with respect to the magnetic sensor 12a. . Next, an example of the detecting device 5b configured as described above will be shown.

FIG. 5 is a block diagram showing an example of a circuit configuration of a detection device 5b according to another embodiment of the present invention. 5, the same elements as those of the detection device 5a shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted or simplified.

In the detection device 5b, the signal S output from the two magnetic sensors 11a and 11b arranged at both ends.
The signal S11 obtained by ORing the 1 and 1a by the OR circuit 21 is input to the logic circuit 15.

The signal S12 output from the logic circuit 15
Is a logical product of the signal S11 and the signal S2, and the signal S1
3 is the negation of the logical sum of the signal S11 and the signal S2.
Therefore, in this detection device 5b, the magnetic sensor 11
Either one of a and 11b and the other magnetic sensor 12 detect the piston 3 (magnet MG) and the time difference.

That is, in the detection device 5b, when the piston 3 is attached to the stroke end position, the position is set so that the magnet MG is detected by either one of the magnetic sensors 11a and 11b and the other magnetic sensor 12. Can be decided According to this detection device 5b, the configuration of the determination circuit 17 can be simplified, and there is an advantage that it is not necessary to consider the left and right directionality when attaching to the stroke end.

According to the above-described embodiment, even in the immediate vicinity of the welding machine, the fluid pressure cylinder 1 and the detection devices 5, 5a, 5 are provided.
b can be used without malfunction. Also,
Since it is possible to use, for example, an inexpensive plastic magnet without making the magnet MG mounted on the piston 3 particularly strong, the cost of the fluid pressure cylinder 1 can be reduced.

In the above-described embodiment, the functions of the logic circuit 15, the time measuring circuit 16, the judging circuit 17, the power-on circuit 19 and the like are implemented by various hard circuits such as transistors, logic elements, semiconductor integrated circuits, or by an appropriate program. It is possible to realize the hardware or software by using the microprocessor or a combination thereof.

In the above embodiment, the detection devices 5, 5
a, 5b configuration, structure, circuit configuration, element type, constant,
The number, arrangement, etc. can be variously changed in accordance with the gist of the present invention.

[0042]

According to the present invention, it is possible to provide a method and apparatus for detecting a moving object that does not become erroneous even with respect to a strong external magnetic field generated by a welding machine or the like without increasing in size or weight.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of arrangement of two magnetic sensors according to a detection method of the present invention.

FIG. 2 is a timing diagram showing a relationship between ON signals and detection signals of the two magnetic sensors shown in FIG.

FIG. 3 is a block diagram showing an example of a circuit configuration of a detection device according to the present invention.

FIG. 4 is a timing diagram showing a signal state of each part of the detection device shown in FIG.

FIG. 5 is a block diagram showing an example of a circuit configuration of a detection device according to another embodiment of the present invention.

[Explanation of symbols]

 MG Magnet (moving object) 3 Piston (moving object) 5, 5a, 5b Detection device 11, 11a, 11b, 12, 12a Magnetic sensor 16 Time measuring circuit (means for measuring time difference) 17 Judgment circuit (output detection signal) means)

Claims (3)

[Claims] 1. A method for detecting whether or not a moving object is located at a specific position by a magnetic field emitted from the moving object, the method being capable of detecting at least two magnetic fields emitted from the moving object.
Two magnetic sensors are arranged at positions distant from each other along the moving direction of the moving object, and when the two magnetic sensors sense a magnetic field at intervals of a predetermined time or more, the movement A method for detecting a moving object, comprising detecting that the object is at a specific position. 2. A method for detecting whether or not a moving object is in a specific position by a magnetic field emitted from the moving object, the method being capable of detecting at least 2 magnetic fields emitted from the moving object.
Two magnetic sensors are arranged at positions distant from each other along the moving direction of the moving object, and when the two magnetic sensors do not sense the magnetic field at intervals of a predetermined time or more, A method of detecting a moving object, comprising detecting that the moving object is not at a specific position. 3. Two magnetic sensors arranged at positions distant from each other, means for measuring a time difference between signals output from the two magnetic sensors, and comparing the time difference with a preset reference time, A device for detecting a moving object according to a comparison result, and a detecting device for a moving object, comprising: