JPH07218211A - Position detector for cylinder - Google Patents

Abstract

PURPOSE:To provide an-apparatus with a longer service life even when a chattering is generated in a reed switch. CONSTITUTION:This position detector for a cylinder has a detection means which detects the position of a piston in response to a magnet mounted on the piston sliding in the body of a cylinder and displays the results by light. The detection means has reed switches 2 and 3 responding to the magnet mounted on the piston, light emitting bodies 16 and 20 to emit varying light and switching elements 14, 21 and 22 to make the light emitting bodies 16 and 20 emit light with a switching by outputs of the lead switches 2 and 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting the position of a piston which reciprocates in a cylinder, and more particularly to a device having an extended durability time under a usage condition susceptible to a high current. .

[0002]

2. Description of the Related Art Sequence control is the mainstream for automatic control of devices including fluid pressure cylinders. The sequence control is control in which each control step is sequentially advanced according to a predetermined order. When the sequence control circuit is assembled, it is necessary to detect the stroke position of the fluid pressure cylinder as a sequential operation condition. Therefore, the cylinder position detecting device is used as a means for detecting the stroke position. As for this cylinder position detecting device, a combination of a reed switch and a permanent magnet has hitherto been generally commercially available and has become the mainstream. By the way, such a cylinder position detecting device is
As described in detail below, a reed switch reacts with a piston equipped with a permanent magnet within a predetermined range, and this is displayed to detect the position of the piston in the cylinder. Therefore,
The user arranges a cylinder switch whose reed switch indicates its reaction with respect to a permanent magnet by the light of a light emitting body on the outer peripheral portion of the cylinder after confirming a predetermined stroke position of the fluid pressure cylinder.

However, the range in which the reed switch reacts with the permanent magnet has a certain width. It suffices if the user can place the center of the cylinder switch at the center position of the range, but it is difficult to adjust the center position only by displaying the light-emitting body. On the other hand, the cylinder detection device is actually used in the factory, and the detection environment may change greatly due to obstacles such as temperature changes and voltage fluctuations. In that case, if the cylinder switch is attached in a biased state, the reed switch may not react with the permanent magnet. Therefore, if the cylinder switch is installed in a biased manner, the cylinder switch may or may not operate depending on various conditions. Then, the reliability of the cylinder switch is lost, and accordingly, the reliability of the device itself under control is reduced. Therefore, in order to improve the reliability of the cylinder switch, that is, the installability, a two-color display type is conventionally used. The structure and operation of the conventional cylinder position detecting device will be described below.

FIG. 5 is a view showing a cross section of a conventional cylinder position detecting device attached to a cylinder.
A piston 52, which is also made of a non-magnetic material, is fitted in a cylindrical cylinder tube 51, which is made of a non-magnetic material such as brass or aluminum alloy, so as to be able to move forward and backward. A permanent magnet 54 is fitted in the piston 52 in its circumferential shape. Further, lid members 55 and 56 are fitted to the front and rear of the cylinder tube 51. Also, the lid member 5 at the left end
An insertion hole 55a is formed in the center of the piston 5, and a piston rod 53 fixed through the center of the piston 52 is slidably fitted in the insertion hole 55a.

On the other hand, in the above fluid pressure cylinder, as shown in FIG. 5, a cylinder switch 57 which reacts with the permanent magnet 54 provided in the piston 52 is arranged at a predetermined position of the cylinder tube 51. . Figure 6
FIG. 6 is a diagram showing circuit components that make up the cylinder switch 57. This is the same type of first and
The second reed switches 62 and 63 are arranged side by side with a predetermined distance offset from each other. A circuit is composed of the first and second reed switches 62 and 63 and the electrical components formed on the upper surface of the substrate 61. Details of this circuit will be described later. Further, both of the reed switches are formed by forming contact points where the magnetic reeds 64 shown by the dotted lines in the drawing are slightly apart from the both ends in the glass tube in which the nitrogen gas is sealed and overlapped. Then, this circuit component is housed by resin-molding the first and second reed switches 62 and 63 on the cylinder side, and an outer iron case or the like as shown in FIG. 5 for dustproof, dripproof and oilproof. ing.

Next, the circuit configuration formed on the substrate 61 will be described. FIG. 7 is a circuit diagram showing the circuit.
A predetermined voltage is applied to the input terminal 71. And
The input terminal 71 is branched into two, one of which is connected to the first reed switch 62 and the other of which is connected to a first red light emitting diode 72 which emits red light when energized.
The reed switch 62 is further branched into two, one of which is connected to the second red light emitting diode 74 and the other of which is
It is connected to a green light emitting diode 76 that emits green light when energized. The green light emitting diode 76 is connected to the second reed switch 63, while the diode 73 connected to the first red light emitting diode 72 is also connected to the second reed switch 63. Further, the second reed switch 63 further includes a second red light emitting diode 74.
It is connected to the output terminal 75 together with the diode 75 connected to.

Next, the operation of the cylinder position detecting device detailed above will be described with reference to graphs. FIG. 8 is a diagram showing an operation chart. Specifically, the horizontal axis indicates the movement position of the permanent magnet 54 attached to the piston,
The vertical axis shows the magnetic flux density applied to the first and second reed switches 62 and 63. Further, the permanent magnet 5 shown on the horizontal axis
Corresponding to the positions of 4, the relationship of the respective light emitting diodes to be operated is shown. By the way, a line drawn by the value of the magnetic flux density M in parallel with the horizontal axis shows the threshold level, and each reed switch responds when the magnetic flux density of the value of M or more is generated.

First, it is assumed that the piston 52 shown in FIG. 5 moves across the cylinder switch 57 from the left side to the right side in the drawing. Then, the permanent magnet 54 has the first and second reed switches 6 having the positional relationship as shown in FIG.
2, 63 will be moved from the left side to the right side. Therefore, when the permanent magnet 54 moves to a predetermined position by the magnetic field generated by the permanent magnet 54,
The magnetic flux density is applied to the reed switch 62. The applied magnetic flux density is shown by the graph of FIG. 8, where graph A is the magnetic flux density applied to the first reed switch 62 and graph B is the magnetic flux density applied to the second reed switch 63. is there. The magnetic flux density is measured at the center of each reed switch, that is, at the contact point of the magnetic reed 64.

Therefore, when the permanent magnet 54 exceeds the point O shown in FIG. 8 due to the movement of the piston 52, the magnetic flux density of the contact portion of the magnetic reed exceeds the threshold level, and the contact portion of the reed switch 62 magnetic lead. Come into contact and close. Therefore, in the circuit shown in FIG. 7, the load current flows from the input terminal 71 to the reed switch 62. And
Since the other reed switch 63 remains open,
The load current further flows to the terminal 75 via the second red light emitting diode 73 and the diode 74, and the cylinder switch 57
The lens (not shown) lights up in red.

Next, when the piston further moves to the right and reaches a position exceeding point P, the magnetic flux density applied to the second reed switch also exceeds the threshold level. Then, both reed switches 62 and 63 are closed. Therefore, in the circuit shown in FIG. 7, the load current flows through the second reed switch 63 via the first reed switch 62 and the green light emitting diode 74 and reaches the output terminal 75. Therefore, the lens of the cylinder switch 57 lights up in green.

When the permanent magnet 54 exceeds the point Q, the first reed switch 62 is opened because the applied magnetic flux density is below the threshold level. Therefore, the load current flows through the first red light emitting diode 72, the diode 73, and the second reed switch 63 to the output terminal 75.
Reach Therefore, the lens of the cylinder switch 57 lights up in red. Then, the magnetic flux density applied to the second reed switch 63 at the position where the permanent magnet exceeds the point R is also below the threshold level, and the cylinder switch 57
Lens becomes unresponsive. A chart showing the operation state of the above light emitting diode is shown in the lower part of FIG.

In the conventional cylinder switch having such a structure, the two-color display type is adopted as described above, and the region where the green light emitting diode 74 reacts is located at a position where the influence of the external magnetic field, the ambient temperature, etc. is small. "The optimum mounting range"), and the first and second red light emitting diodes 72, 73
The area in which the reaction of is indicated is a position (this is called "dangerous mounting range") that is easily affected by the external magnetic field, ambient temperature, and the like.
Therefore, the user mounts the cylinder switch 57 on the cylinder tube 51 at a position where the contact portion of the magnetic lead is in the optimum mounting range with respect to the permanent magnet 54 when the piston 52 is arranged at a predetermined position.

[0013]

However, such a conventional cylinder switch has a problem that the following inconvenience occurs. Now, assuming that the permanent magnet 54 is arranged at the position shown in FIG. 9, the first and second reed switches 62, 6 are
A magnetic flux density exceeding the threshold level is applied to both of them. Therefore, the first and second reed switches 62 and 63
Are closed and the green light emitting diode 74 is turned on. At this time, the first reed switch 62 is applied with the preliminary magnetic flux density of the value a based on the threshold level M, while the second reed switch 63 is applied with the preliminary magnetic flux density of the value b.

In such a state, when a magnetic field is applied from the outside and the magnetic shield case reaches magnetic saturation, the magnetic field is also applied to the reed switch. In particular, the current used in the spot welding machine used in the automobile manufacturing process is a high current, and a strong magnetic field is generated around the spot welding operation. Therefore, when the cylinder position detecting device is used around the spot welder, the second reed switch 63 malfunctions and opens when the external magnetic field exceeds the value of b, while the first reed switch 62 is opened. Is added with a sufficiently large preliminary magnetic flux density a, the closed state is maintained. As a result, the cylinder switch 57
The lighting of the lamp (not shown) changes from green to red.

Further, when this external magnetic field is one which generates an alternating magnetic field as in the above spot welder or the like, for example, the spot welder generates an alternating magnetic field of 50/60 Hz. Therefore, the second reed switch 63 is repeatedly opened and closed 100/120 times per second, and red and green are repeatedly lit each time. By the way, a load current of about 10 mA flowing through the circuit causes a spark when the magnetic material leads come into contact with each other. Therefore, when the reed switch is repeatedly opened and closed in this manner, the contact portion of the magnetic lead 64 is melted by the heat of the spark, and finally the contact portion is welded to function as a cylinder switch. I can't do it. It has been confirmed by experiments that the life of the reed switch at this time is about 10 million times of contact operation with a load current passing through the reed switch of 10 mA.

Therefore, it is assumed that the conventional position detecting device for a cylinder described above is used, for example, in an automobile production line, particularly in an automobile body line using the spot welding machine.
Then, with the production volume of 1000 automobiles per day, the number of welding times per vehicle is 10 times, the time per welding point is 0.5 seconds,
Under the condition that the welding current frequency is 60 Hz, the reed switch contact operation is 1000 * 10 * 60 = 600,000 times per day, and the reed switch contact operation is 10 million times in 17 days from the start of use with a load current of 10 mA. There is a possibility that welding may occur at the switch part. The malfunction of the detection device is dangerous because interference with other devices may occur during the sequence control process. Also,
The cost burden due to the repair and replacement also increases.

An object of the position detecting device for a cylinder of the present invention is to solve the above-mentioned problems and to prevent a malfunction occurring in a reed switch, and to provide a device having a long life even if a malfunction occurs. To do.

[0018]

A cylinder position detecting device according to the present invention includes a detecting means for detecting a piston position in response to a magnet mounted on a piston sliding in a cylinder body and displaying the position with light. A position detecting device for a cylinder, wherein the detecting means has a reed switch that responds to a magnet mounted on a piston, a light emitting body that emits light, and a switching element that causes the light emitting body to emit light by switching by the output of the reed switch. And have. Further, in the above-mentioned one, the reed switch has two or more and detects different positions of the piston, the light emitter has two or more and emits different lights, and the switching element has
It is characterized in that there are two or more and the output of the reed switch causes the light-emitting body corresponding to the reed switch to emit light.

[0019]

The cylinder position detecting device of the present invention having the above structure operates as follows. When the driving air is supplied to the cylinder, the piston equipped with the magnet slides in the cylinder body. The reed switch of the detection means mounted on the outer peripheral portion of the cylinder body is connected by the magnet mounted on the piston when the piston is within the predetermined range. By connecting the reed switch, the switching control terminal of the switching element connected in series with the reed switch is energized. The switching element makes the switching terminal conductive when the switching control terminal is energized. Since the power source is connected to one side of the switching terminal and the light emitting body is connected to the other end of the switching terminal, the light emitting body is energized by this, and the light emitting body emits light. As described above, the reed switch does not directly energize the light emitter to emit light, but energizes the light emitter through the switching element to emit light, so that the current flowing through the reed switch is small and chattering occurs in the reed switch. Even if it happens, there will be no trouble of welding the reed switch.

Two reed switches fixed at a predetermined distance from each other, when the two reed switches are both on, energize the green light emitting diode to emit green light, and one reed switch is on. When the other reed switch is off, the red light emitting diode is energized to emit red light. The user positions the cylinder position detecting device by fixing the cylinder position detecting device while the reed switch emits green light. At this time, if the cylinder position detection device is fixed to the end of the region where the green light emitting diode emits light, chattering occurs in both the reed switch that energizes the green light emitting diode and the reed switch that energizes the red light emitting diode. There is a fear. In particular, when a spot welder is nearby and a strong magnetic field is generated by an alternating high current, chattering is likely to occur in the reed switch.
Even if chattering occurs in the reed switch, the current flowing through the reed switch is small, so sparks are less likely to occur due to chattering, and the contacts of the reed switch are not welded.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. The cylinder position detecting device of the present embodiment also has a cylinder switch for confirming the position of the piston sliding inside the cylinder at a predetermined position of the cylinder tube as in the conventional device. Figure 1
It is the figure which showed the cross section of the cylinder switch of the position detecting device for cylinders of 1st Example. The cylinder switch of this embodiment has the following structure. First, like the conventional one, the indicator light circuit is formed on the upper part of the substrate 1,
Further, first and second reed switches 2 and 3 are formed in the lower part. The first and second reed switches 2 and 3 are moved back and forth by a predetermined distance as in the conventional case.

The electrical components formed above and below the board 1 are filled with an internal filling resin 4 for protecting water and oil from entering, and further vibration and shock, and the board 1 is made of iron or the like on the resin case 5. Is covered with the first shield case 6 made of magnetic material. Further, the resin case 5 is covered with a second shield case 7 that is also made of a magnetic material such as iron and has a size that encloses the first shield case 6. In addition, a lens 8 is formed on the second shield case 7 for penetrating the first shield case 6 and the inner filling resin 4 in a straight line to emit the light of the light emitting diode on the substrate 1 described below to the outside. There is. Then, a lead wire 9 is wired to a load such as a programmable controller (not shown).

Next, the internal circuit formed on the substrate 1 will be described. FIG. 2 is a diagram showing an internal circuit of the cylinder switch of this embodiment. The first reed switch 2 connected to the input terminal 11 to which a predetermined voltage is applied is connected to the base of the first transistor 14 via the resistor 13. The emitter of the first transistor 14 is connected to the red light emitting diode 16 via the diode 15 and to the output terminal 25. On the other hand, the collector of the first transistor 14 is connected to the input terminal 11. The second reed switch 3 connected to the input terminal 11 is also connected to the base of the second transistor 19 via the resistor 18. And the second transistor 1
The emitter of 9 is connected to the diode 15 and the collector is connected to the input terminal 11.

Further, the green light emitting diode 20 connected to the input terminal 11 includes the third and fourth transistors 21 and 22.
It is connected to the output terminal 25 via. At this time the third
The collector of the transistor 21 is the green light emitting diode 20.
The emitter is connected to the collector of the fourth transistor 22. The emitter of the fourth transistor 22 is connected to the output terminal 25. On the other hand, the bases of the third and fourth transistors 21 and 22 have resistors 23 and
It is connected to the second reed switch 3 and the first reed switch 2 via 24.

The cylinder switch of this embodiment having the above-described structure operates as follows. At this time, as in the conventional one, the magnetic reed of the reed switch responds at a threshold level or higher, and as shown in FIG.
Distinguished by Q and QR. First, when the point O is exceeded, the first reed switch 2 is closed by the permanent magnet arranged in the piston. Then, the base current flows through the first transistor 14 and the fourth transistor 22. Therefore, the collector-emitter of the first transistor 14 is in the ON state and a current flows, but the current does not flow between the collector-emitter of the second transistor 22 because the third transistor is in the OFF state. Therefore, only the red light emitting diode 16 reacts, and the lens 8 emits red light.

Next, when point P is exceeded, both the first and second reed switches 2 and 3 are closed. At this time, the first
The base current flows through all of the fourth transistors 14, 19, 21, and 22. But most of the load current is
It flows to the output terminal 25 through the green light emitting diode 20, the third transistor 21, and the fourth transistor 22. This is because the current tends to flow through a path having a low internal drop voltage, and the diode 15 is connected in series to the red light emitting diode 16 to increase the resistance value on the red light emitting diode 16 side. Is. Therefore, only the green light emitting diode 20 reacts, and the lens 8 emits a green light.

Further, when point Q is exceeded, only the second reed switch 3 is closed, and the second and third transistors 1
A base current flows in 9, 21. However, since the fourth transistor 22 remains in the OFF state, no current flows between the collector and emitter of the third transistor 21, and only the current flows between the collector and emitter of the second transistor 19. Therefore, only the red light emitting diode 16 responds,
A red light is lit on the lens 8.

Therefore, also in the position detecting device for a cylinder of this embodiment, when a strong alternating magnetic field is generated in the state shown in FIG. 9, the contact portion of the magnetic reed of the reed switch is the same as the conventional one. The opening and closing of will be repeated. However, in the present embodiment, both the first reed switch 2 and the second reed switch 3 are connected to the bases of the first to fourth transistors 14, 19, 21, 22 and most of the load current is in each transistor. It will flow between the collector and the emitter. Therefore, only a small amount of load current flows through the first reed switch 2 and the second reed switch 3.

Specifically, it is as follows. That is,
The current value IB flowing through the reed switch is determined by the load current value IC and the current amplification factor hFE of the transistor.
It is represented by B = IC / hFE. Now, suppose that IC = 10mA, hF
When E = 160, IB = 10 (mA) / 160,
Values of about 63 μA can be obtained. This means that when a current of 10 mA is required to make the light emitting diode emit light, a current of 63 μA should be passed through the transistor. Therefore, in this embodiment, the current value flowing through the reed switch can be reduced to 1/150 or less as compared with the conventional one, and even when chattering occurs,
The reed switch reduces the occurrence of sparks and prevents the terminals from welding. As a result, the life of the cylinder switch is significantly extended, and according to experiments, the opening / closing operation of the reed switch can be extended to 600 million times, and until the reed switch is welded by the same calculation as before,
It could be used for 1000 days or more. This is a life extension of about 60 times that of the conventional one. In addition, the double shield case has made it possible to reduce the influence of the external magnetic field.

Next, the second embodiment will be described. This embodiment has the same structure as that of the first embodiment and the substrate 1
The circuit formed in is different. The circuit is shown in FIG. In the circuit of this embodiment as well, the same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. In this, the input terminal 11 and the output terminal 25 of the circuit of the first embodiment are connected via the diode bridge 31, and the input and output terminals 32 and 33 are connected to the other terminals of the diode bridge 31. In this example, an AC power source is used as the power source. As in the first embodiment, most of the load current flows between the collector and emitter of each transistor. Therefore, only a small amount of load current flows through the first reed switch 2 and the second reed switch 3 connected to the base.

Therefore, as in the first embodiment, the current value flowing through the reed switch is remarkably reduced, and it is possible to provide a position detecting device for a cylinder whose life is greatly extended. By adding the diode bridge 31, the cylinder switch of the first embodiment is DC
Although it is used exclusively, the present embodiment can also be used for AC, and it is possible to provide a cylinder position detection device for both AC and DC.

Further, a third embodiment will be described. The cylinder position detecting device of this embodiment also has the same configuration as that of the first embodiment, and the internal circuit formed on the substrate 1 is different. Therefore, FIG. 4 shows a circuit diagram of this embodiment. Note that the same reference numerals are given to the same configurations in the circuit,
The description is omitted. In this embodiment, the first shown in FIG.
In the circuit of the embodiment, the first to fourth transistors 1
4, 19, 21, and 22 are replaced with first to fourth triacs 41, 42, 43, and 44, respectively.
The gate of each triac is connected to the first and second reed switches 2 and 3 in series via the resistors 13, 18, 23 and 24. A diode 45 and a diode 46 are connected in parallel with the diode 15, the red light emitting diode 16, and the green light emitting diode 20, respectively. This is to prevent the light emitting diodes 16 and 20 from being damaged when a reverse voltage is applied.

Therefore, with this structure, even when the triac is used as in the present embodiment as in the case of the first embodiment, only a small amount of load current flows through the gate and the first connection is made to the gate. Only a small amount of load current will flow through the first reed switch 2 and the second reed switch 3 as well. As described above, in the present embodiment, the position detecting device for a cylinder, which is dedicated to AC using the triac, and whose current value flowing through the reed switch is remarkably reduced and its life is remarkably extended, as in the first embodiment. Can be provided.

Although the embodiments of the cylinder position detecting device of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. is there. For example, in the above embodiment, a transistor, a triac, or the like is used, but the circuit component is not limited to this, and an SCR or the like can be used as the same effect. Further, for example, although red and green are used for the light emitting diodes in the above embodiment, the light emitting diodes are not limited to these colors, and there is no problem in using other colors.

[0035]

As is apparent from the above description,
In the cylinder position detecting device of the present invention, the detection means for detecting the piston position in response to the magnet mounted on the piston sliding in the cylinder body is a reed switch responsive to the magnet mounted on the piston, and an optical sensor. Since it has a light-emitting body that emits light and a switching element that switches the light-emitting body to emit light by switching the output of the reed switch, the amount of current flowing through the reed switch is reduced. In addition, the number of times until welding occurs at the contact portion of the reed switch can be significantly increased, and it is possible to provide a detection device having a long life.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross section of a detection means of a cylinder position detection device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an internal circuit of the cylinder switch according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an internal circuit of a cylinder switch according to a second embodiment of the present invention.

FIG. 4 is a diagram showing an internal circuit of a cylinder switch according to a third embodiment of the present invention.

FIG. 5 is a view showing a cross section of a state in which a conventional cylinder position detecting device is attached to a cylinder.

FIG. 6 is a diagram showing a side surface of a circuit component of a conventional cylinder position detecting device.

FIG. 7 is a diagram showing an internal circuit of a conventional cylinder switch.

FIG. 8 is a diagram showing a magnetic flux density generated in a reed switch and an operation chart.

FIG. 9 is a diagram showing a magnetic flux density generated in a reed switch.

[Explanation of symbols]

 1 Substrate 2 First Reed Switch 3 Second Reed Switch 4 Inner Filling Resin 5 Resin Case 6 First Shield Case 7 Second Shield Case 8 Lens 14 First Transistor 16 Red Light Emitting Diode 19 Second Transistor 20 Green Light Emitting Diode 21 Third Transistor 22 4th transistor

Claims (2)

[Claims] 1. A position detecting device for a cylinder, comprising: a detecting unit for detecting a piston position and displaying the result by light in response to a magnet mounted on a piston sliding in a cylinder body. A position detecting device for a cylinder, comprising: a reed switch that responds to a magnet attached to a piston, a light emitting body that emits light, and a switching element that switches by the output of the reed switch to cause the light emitting body to emit light. 2. The cylinder position detecting device according to claim 1, wherein the reed switch has two or more to detect different positions of the piston, and the light emitter has two or more to emit different lights. A position detecting device for a cylinder, which emits light, and wherein the switching element has two or more, and an output of the reed switch causes a light emitting body corresponding to the reed switch to emit light.