JPH0515042Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a piston position detection device that detects the position of a reciprocating piston using fluid pressure.

[Prior Art] Pistons that reciprocate within cylinders using fluid pressure have traditionally been used in various industrial equipment, such as robots and
Widely used in NC machine tools, etc. In order to monitor the operating status of these various industrial devices, it is effective to know where the piston is located within the cylinder, and various piston position detection devices have been put into practical use. Among them, those that attach a magnetic field generating member such as a permanent magnet to the piston and detect the magnetic field from the magnet are more reliable than those that use limit switches that open and close mechanical contacts. It is widely used because it has the advantages of high energy efficiency, low cost compared to those using photoelectric switches that detect optical changes, and ease of handling.

[Problems to be Solved by the Invention] However, even the piston position detection device of the type that detects the magnetic field as described above is still not satisfactory, and the following problems have occurred.

Since the piston position detection device is applied to various industrial equipment as described above, the environment in which it is used is extremely harsh such as a factory. Therefore, the piston position detection device is sometimes placed in a strong magnetic field other than the magnetic field generated by a magnetic field generating member such as a permanent magnet attached to the piston, and detects other disturbance magnetic fields to detect the magnetic field as if it were coming from the piston. This results in false detection. For example, when a cylinder is used in a hydraulic control system of a welding robot, a conductive wire carrying a large current required for welding may swing in the vicinity of a piston position detection device. In this case, a magnetic field caused by the current, that is, an alternating magnetic field as a disturbance magnetic field that changes with the frequency of the commercial power source acts on the piston position detection device.

As a solution to this problem, a so-called directional type has been proposed, in which the piston position detection device is housed in a magnetically shielded case and has increased sensitivity only to the magnetic field generated from the direction of the cylinder. . However, even with this, there is a drawback that malfunction occurs when the intensity of the disturbance magnetic field exceeds a certain level, and it does not have sufficient reliability.

The present invention was developed in view of the above problems, and is a magnetic field detection type piston position detection device that is inexpensive and easy to handle due to its operating principle, and is an excellent piston position detection device that can completely avoid malfunctions caused by disturbance magnetic fields. Its purpose is to provide a position detection device.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the means constructed in the present invention is to attach a magnetic field generating member to a piston that reciprocates inside a cylinder by fluid pressure, and to generate a magnetic field by the magnetic field generating member. A piston position detection device that detects the position of the piston by detecting a magnetic field generated by the piston, comprising: a first magnetic field detection means that is provided outside the cylinder and detects a magnetic field from the magnetic field generating member; a second magnetic field detection means that is provided near the detection means and detects a magnetic field with higher sensitivity than the first magnetic field detection means with respect to a disturbance magnetic field that acts from outside the cylinder and whose magnitude changes periodically; and the detection result of the first magnetic field detection means and the second magnetic field detection means.
and the detection results of the magnetic field detection means, and the second
When the magnetic field detecting means does not detect a disturbance magnetic field, the detection result of the first magnetic field detecting means is output, and when the second magnetic field detecting means detects a disturbance magnetic field, it outputs the detection result of the disturbance magnetic field before the detection of the disturbance magnetic field. The gist of the present invention is a piston position detection device characterized by comprising: output selection means for maintaining and outputting the detection result of the first magnetic field detection means.

[Operation] The piston position detection device of the present invention includes two magnetic field detection means, a first magnetic field detection means and a second magnetic field detection means, outside the cylinder. As sensors for detecting magnetic fields, there are sensors based on various operating principles, such as Hall elements, magnetoresistive elements, and reed switches, and any of them may be used. The first magnetic field detection means detects the magnetic field of the magnetic field generating member attached to the piston. Further, the second magnetic field detection means has a generation source outside the cylinder than the first magnetic field detection means, and detects the magnetic field with high sensitivity to a disturbance magnetic field in which the magnitude of the magnetic field changes periodically. . The detection results of these two magnetic field detection means are both input to the output selection means, and when the second magnetic field detection means does not detect the above-mentioned disturbance magnetic field, the detection result of the first magnetic field detection means is accurate. It is determined that the position of the piston is reflected in the position of the piston, and the detection result of the first magnetic field detection means is output as is. Further, when the second magnetic field detection means detects a disturbance magnetic field, it is assumed that the previous detection result of the first magnetic field detection means accurately reflects the piston position.
The previous detection result output of the first magnetic field detection means is held.

Hereinafter, the piston position detecting device of the present invention will be described in more detail with reference to examples.

[Example] Fig. 1 is a schematic diagram showing a piston position detection device according to an example installed in a cylinder, in which figure A is a cross-sectional view taken along the axis of the cylinder, and figure B is a cross-sectional view taken along the axis of the cylinder. A' cross-sectional view is shown. As shown in the figure, inside the cylinder 10 is a piston 12 that reciprocates in the direction of the arrow using fluid pressure such as air pressure or oil pressure.
are fitted. A ring-shaped groove 14 is formed in the circumference of this piston 12, and the groove 1
4 has an annular permanent magnet 16 fitted therein.
The piston position detection device 20 of the embodiment installed in the cylinder 10 detects the magnetic field from the permanent magnet 16 to detect the sliding condition of the piston 12. As shown in FIG. The first Hall element (including a signal processing circuit that converts a minute signal into a logic level and outputs the signal) 22 detects that the magnetic field near the piston position detection device 20 has become stronger as the magnetic field approaches the vicinity directly below the piston position detection device 20. Detect with. The piston position detection device 20 has a built-in second Hall element 24 (including a signal processing circuit that converts a minute signal into a logic level and outputs it) which is another Hall element, which is different from the first Hall element described above. It is placed on a shield box 26 that shields the Hall element 22 from external magnetic fields. Therefore, the first Hall element 22 operates to detect a magnetic field whose source is inside the cylinder 10, that is, the magnetic field whose source is the permanent magnet 16, with higher sensitivity than the second Hall element 24. On the other hand, in response to a disturbance magnetic field whose source is outside the cylinder 10 and whose magnitude changes periodically, the second Hall element 24 acts as the first
The detection operation is performed with high sensitivity compared to the Hall element 22. In this way, the outputs of the two Hall elements 22 and 24, which detect different magnetic fields, are input to the output processing circuit 28, which will be described later, and then subjected to predetermined processing, resulting in the final detection output as the piston position detection device 20. is obtained. The piston position detection device 20 is housed in a case 30 made of a non-magnetic material such as resin in order to increase mechanical strength and protect it from floating dust and the like.

FIG. 2 is a detailed electrical circuit diagram of the output processing circuit 28 described above. This output processing circuit 28 includes a set of + and - power supply terminals for receiving power supply.
It is equipped with three terminals: TSP, TSN, and a signal terminal TO for outputting the piston position detection results, and is connected to external equipment via these terminals.
The two Hall elements 22 and 24 described above are connected between the power supply terminals TSP and TSN and receive power supply. Similarly, the latch IC 32 that inputs the outputs of the two Hall elements 22 and 24 also has power terminals TSP,
Powered by TSN, light emitting diode 34
and ON/OFF control of the base current of the switching transistor Tr via the current limiting resistor 36.
That is, when the latch IC 32 produces an output, the light emitting diode 34 emits light and the transistor Tr
The signal terminal TO connected to the collector of the latch IC 32 is set to a low impedance of the ground level, and when there is no output from the latch IC 32, the light emitting diode 34 is turned off and the signal terminal TO is set to an open level.

FIG. 3 is an input/output state diagram of this latch IC 32. As shown in the figure, the output of the latch IC 32 is the same as the output of the first Hall element 22 when the output of the second Hall element 24 is at a low level (hereinafter referred to as "L"), and the output of the second Hall element 24 is " This is a normal latch logic circuit that maintains the previous output of the first Hall element 22 when changing from the "L" level to the High level (hereinafter referred to as "H").

Next, regarding the detection operation of the piston position detection device 20 configured as described above, firstly, when there is no disturbance magnetic field, and secondly, when there is a disturbance magnetic field and the magnetic field from the piston 12 is not detected, Thirdly, three cases will be explained in which there is a disturbance magnetic field and the magnetic field from the piston 12 is also detected at the same time.

Figure 4A shows the first case when there is no disturbance magnetic field,
FIG. 3 is an explanatory diagram of the outputs of the second Hall elements 22 and 24 and the latch IC 32. As the piston 12 moves as shown in the figure, the magnetic field generated by the permanent magnet 16 at the position where the piston position detection device 20 is arranged is increased from 0 to G1.
When the value changes to [Gauss], the output of the first Hall element 22 changes accordingly to "L" and "H" accurately following the change. At this time, since the second Hall element 24 is excluded from the influence of the magnetic field from the permanent magnet 16 by the magnetic shielding effect of the shield box 26,
Its output is always "L". Therefore, the latch
The output of the IC 32 is the same as the output of the first Hall element 22, and a detection output corresponding to the position of the piston 12 is obtained.

Figure 4B shows an alternating current, that is, a strong magnetic field (-G2 to +G2) that changes periodically in magnitude and direction.
[Gauss]) acts on the piston position detection device 20 as a disturbance magnetic field. At this time, the output of the second Hall element 24 is "H" when the magnitude of the detected disturbance magnetic field reaches a large value exceeding the threshold level ±G3. In the illustrated example, the magnetic field from the permanent magnet 16 from the piston 12 is not acting, and therefore only the disturbance magnetic field is acting on the first Hall element 22 as well. However, the magnetic field detection sensitivity of the first Hall element 22 with respect to the disturbance magnetic field is kept low compared to the detection sensitivity of the second Hall element 24 due to the magnetic shielding effect of the shield box 26, and the disturbance magnetic field is ±G4 (>± G3) produces an "H" output only when it is stronger than G3). When the outputs of the first and second Hall elements 22 and 24 change in this way, the output of the latch IC 32 corresponds to the output of the first Hall element 2 before the second Hall element 24 detects the magnetic field.
Since it maintains the output of 2, it always shows the output of "L" and accurately reflects the piston position detection result as in the above-mentioned figure A.

Next, using Figure 4C, we can see that there is a disturbance magnetic field (-G2 to +G2 [Gauss]) as shown in Figure B above.
A case will be described in which the piston position is near the piston position detection device 20. The disturbance magnetic field is the time
When it occurs at t1, the second Hall element 24 exhibits the same output change as described above in response to the magnetic field change. In addition, the output of the first Hall element 22, which had detected the magnetic field from the permanent magnet 16 before the disturbance magnetic field was generated, may maintain the initial "H" output for a short time after time t1, but it will remain permanently. Magnetic field from magnet 16 +
If the disturbance magnetic field becomes strong enough to cancel G1 (-G5), it may change to "L".
Then, when the disturbance magnetic field becomes even stronger (-G6), a magnetic field in the opposite direction is detected and the output is reversed again to become "H". In this way, the first Hall element 22
When the disturbance magnetic field has the opposite polarity to the magnetic field generated by the permanent magnet 16, the output may undergo repeated changes. However, even in this case, the second Hall element 24, which is highly sensitive to the disturbance magnetic field, detects the disturbance magnetic field and changes its output to "H" before the output of the first Hall element 22 changes. , the latch IC32 output always maintains "H" reflecting the piston position.

Piston position detection device 2 that operates as described above
0, no matter how strong the disturbance magnetic field is generated, its output always accurately reflects the piston position, making it possible to perfectly monitor the operating status of the fluid pressure cylinder. This is also clear from the empirical rule that most of the disturbance magnetic fields generated at the location where the piston position detection device 20 is normally arranged are alternating magnetic fields caused by large currents obtained from the commercial power source. That is, the disturbance caused by the alternating magnetic field changes at 50 or 60 Hz, and therefore there are moments when the magnetic field becomes "0" 100 or 120 times per second. At this time, the output of the second Hall element 24 becomes "L", and the latch IC captures the latest output of the first Hall element 22, thereby detecting the piston position detection device 20 even when disturbances are continuously occurring. The output accurately reflects the piston position.

In the above-described embodiments, the source of the disturbance magnetic field is an alternating current that changes sinusoidally, that is, the magnitude of the magnetic field changes periodically, and the direction of the magnetic field also changes periodically. explained. However, the disturbance magnetic field in the present invention may be anything as long as the magnitude of the magnetic field changes periodically, for example, an alternating current and a direct current are superimposed, and the magnitude changes periodically but the direction is opposite. This can be done in the same way even with pulsating currents that should not be used.

When affected only by the above-mentioned alternating current, the direction of the magnetic field also reverses periodically, so as shown in Figure 4, the threshold level (±G3)
is set to both positive and negative. On the other hand, if the present invention is carried out in the case of a positive-only pulsating current, for example, only a positive-only threshold level is set, and the other configurations and operations are the same.

[Effects of the Invention] As described above in detail with reference to the embodiments, the piston position detection device of the present invention uses the detection result of the first magnetic field detection means for detecting the magnetic field from the piston to be detected by the first magnetic field detection means. The second type is highly sensitive to disturbance magnetic fields that act from the outside and whose magnitude changes periodically.
It is determined whether or not the magnetic field is accurate based on the detection result of the magnetic field detection means. Therefore, no matter how strong the disturbance magnetic field is, the piston position can always be detected accurately, resulting in a piston position detection device that is inexpensive, easy to handle, and highly accurate.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a piston position detection device which is an embodiment of the present invention, in which figure A is a cross-sectional view along the cylinder axis, figure B is a cross-sectional view taken along line A-A',
Figure 2 is an electric circuit diagram of the example, Figure 3 is an input/output characteristic diagram of the latch IC used in the electric circuit,
FIGS. 4A, 4B, and 4C each show a timing chart representing the operating state of the piston position detection device of the embodiment. 10...Cylinder, 12...Piston, 16...
...Permanent magnet, 20...Piston position detection device, 2
2...First Hall element, 24...Second Hall element, 32...Latch IC.

Claims (1)

[Claims for Utility Model Registration] In a piston position detection device in which a magnetic field generating member is attached to a piston that reciprocates inside a cylinder by fluid pressure, and the position of the piston is detected by detecting the magnetic field generated by the magnetic field generating member. , a first magnetic field detection means provided outside the cylinder for detecting the magnetic field from the magnetic field generation member; and a first magnetic field detection means provided near the first magnetic field detection means acting from the outside of the cylinder so as to detect the magnetic field. a second magnetic field detection means that detects a magnetic field with higher sensitivity than the first magnetic field detection means with respect to a periodically changing disturbance magnetic field;
and the detection results of the magnetic field detection means, and the second
When the magnetic field detection means is not detecting the disturbance magnetic field, the detection result of the first magnetic field detection means is output, and when the second magnetic field detection means is detecting the disturbance magnetic field, the disturbance magnetic field is detected. A piston position detection device comprising: output selection means for maintaining and outputting a previous detection result of the first magnetic field detection means.