JPS6358102A - Piston position detecting circuit for cylinder - Google Patents

Abstract

PURPOSE:To enable the stabilization of ON-OFF control of a load, by driving the read switch by a constant current to extend the life of the contact thereof while the detection sensitivity of a piston position is maintained high. CONSTITUTION:As the read switch 3 reaches a certain part with the movement of a piston in a cylinder, influenced by the magnetic field of the magnet possessed by the piston, the switch 3 is turned ON in an area where the magnetic field exceeds a specified level. The switch 3 causes chattering when the magnetic field crosses over a specified level. With such actions of the switch 3, an integrated output is obtained in a filter circuit 5 and after shaping of the waveform thereof with a buffer amplifier 6, the output is inverted and inputted into an output transistor 7. Thus, the transistor 7 underdoes ON or OFF operation and acts to supply source power to a load during the ON-period. That is, the switch 3 is always ON by a constant current, hence free from direct reception of abnormal voltage and current thereby eliminating melt welding or burning out of the contact thereof 3.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a piston in a cylinder that protects a reed switch that supplies and cuts off power to a load by detecting the position of the piston moving within the cylinder and opening and closing it. This invention relates to a position detection circuit.

[Conventional technology]

BACKGROUND ART A cylinder piston position detection circuit that opens and closes a sensor switch in response to the displacement of a piston within a cylinder to control the supply of power to a load is widely used in hydraulic and pneumatic control systems.

As the sensor switch, non-contact switches such as reed switches, magnetic resistance elements, and Hall elements, which are magnetically opened and closed in response to the piston position, are widely used. Note that such a sensor switch is usually placed on the outer periphery of the cylinder at a position corresponding to both ends of the movable region of the piston or at an intermediate position therebetween.

[Problem that the invention seeks to solve]

However, when the above-mentioned reed switch is used as a sensor switch, when an inductive load or a large current resistive load is connected to it, it is necessary to insert a spark suppression circuit, mainly a CR circuit, in parallel with the reed switch. Also, when connecting a lamp load, a reed switch protection circuit is required to suppress rush current immediately after lighting. Furthermore, if the wiring capacity is large or if a capacitive load is connected, a surge suppressor circuit or the like is required to suppress the surge current flowing through these. In other words, depending on the type and size of the load, the reed switch contacts may weld, melt, or
Protection circuits for preventing carbonization must be selectively used, and these selection operations are troublesome for users.

-4. Sensor switches that use non-contact switches have the advantage of long life, but because they have a temperature coefficient, the operating distance of the rod is not constant due to temperature changes, and the detection sensitivity of the piston position is poor. There were some problems, such as:

The present invention has been made to solve such conventional problems, and its purpose is to suppress the heat generation of the reed switch contacts and extend the life of the contacts by driving the reed switch with a constant current. An object of the present invention is to obtain a cylinder piston position detection circuit capable of stabilizing load on/off control while maintaining high position detection sensitivity.

[Means for solving problems]

The cylinder piston position detection circuit according to the present invention has a constant current circuit that flows an appropriate constant current while the reed switch is in operation, between the power supply side of the reed switch and the load.
It consists of a filter circuit that absorbs chattering when the reed switch opens and closes, and an output transistor that controls the power supply to the load based on the output of this filter circuit.

[Effect]

The constant current drive of the reed switch in the present invention extends the life of the contacts, but this firstly prevents the generation of sparks due to large currents and inductive loads, and the increase in contact resistance of the contacts due to minute currents, and prevents the contact resistance of the reed switch from increasing. acts to protect.

Further, the filter circuit according to the present invention absorbs chattering when the reed switch is opened and closed by its integral action. Furthermore, the power supply to the load is controlled by an output transistor that turns on and off in response to the opening and closing of the reed switch, so the reed switch is always driven in a constant current circuit regardless of the size or type of load. , operates to enable highly reliable operation of the piston position detection circuit.

〔Example〕

One embodiment of the present invention will be described based on the drawings. FIG. 1 shows, for example, a piston position detection circuit of a pneumatic cylinder, and this piston position detection circuit is composed of a sensor section 1 and an output circuit section 2. There is. Further, the sensor section 1 includes a reed switch 3 connected to a constant current circuit 4.

On the other hand, the output circuit section 2 includes a filter circuit 5 connected to the reed switch 3 and one end of the constant current circuit 4, a buffer amplifier 6 that shapes the output waveform of the filter circuit 5, and a base based on the output of the buffer amplifier 6. It consists of an output transistor 7 that is turned on and off in response to the current, and a light emitting diode 8 for an indicator that is turned on by the output of the buffer amplifier 6. Further, the emitter of the output transistor 7 is grounded, and the collector is connected to a power supply via a load (not shown). Diode 9 is a diode for preventing damage to the internal circuit due to reverse connection.

Next, the operation of this circuit will be explained with reference to the time chart of signal waveforms of each part of the circuit shown in FIG.

Now, when the piston in the cylinder moves and reaches the part where the reed switch 3 is located, it receives a magnetic field from the magnet of the piston as shown in FIG. Then, the reed switch 3 is turned on. Note that this reed switch 3 causes chattering when the voltage exceeds the predetermined level and when the voltage falls below the predetermined level, as shown in FIG. By such an operation of the reed switch 3, the filter circuit 5 obtains an integrated output as shown in FIG.
) is inverted and input to the output transistor 7. Therefore, the output transistor 7 turns on and off as shown in FIG. 2(e), and operates to supply power to the load (not shown) during the on period. In other words, since the reed switch 3 is always turned on with a constant current and is not directly affected by abnormal voltage or abnormal current depending on the size or type of load, the contacts of the reed switch 3 may become welded.
No more melting.

FIG. 3 shows another embodiment. This is a more specific version of the circuit diagram in Figure 1, in which a stabilized power supply circuit 11 and a capacitor 12 are connected to the positive DC power supply circuit, and a current flows between the stabilized power supply circuit 11 and the reed switch 3. A limiting resistor 13 is connected to constitute a constant current circuit 4, a resistor 14 and a capacitor 15 are connected as a filter circuit 5, a resistor 16 is connected to a buffer amplifier 6 for waveform shaping, and buffer amplifiers 17 and 18 for current amplification are connected. furthermore, the output transistor 7
A resistor 19 and a resistor 20 are connected to the base of the output transistor 7, and a Zener diode 21 is connected between the emitter and the collector of the output transistor 7. The basic operation and effects of this embodiment are similar to those described with reference to FIG. Here, the current flowing through the reed switch 3 is further stabilized by the stabilized power supply circuit 11, and the voltage applied to the load is limited to a constant voltage value by the Zener diode 21.

FIG. 4 shows yet another embodiment. This has a current limiting resistor 21a1 light emitting diode 22,
A reed switch 3 and a resistor 23 are connected in series, of which the light emitting diode 22, the reed switch 3 and the resistor 2
A Zener diode 24 is connected in parallel to a series circuit consisting of 3. Note that other parts are substantially the same as those shown in FIG. 3, so the same parts are denoted by the same reference numerals and redundant explanation thereof will be omitted. The basic operation and effects of this circuit are substantially the same as those of the above embodiments. Here, a constant current circuit 4 is constructed by connecting a current limiting resistor 21a and a Zener diode 24 in series to a DC power source, and the voltage between the anode side of the light emitting diode 22 and the negative side power source of the resistor 23 is kept constant, and the lead The current flowing through the switch 3 is made constant.

In this way, in each of the above embodiments, the reed switch 3, which opens and closes depending on the piston position, is operated in a constant current circuit, so that the voltage and current flowing to the load are prevented by turning on and off the reed switch. Even if this happens, there will be no adverse effect on the contacts of the reed switch 3.

Note that the present invention is not limited to the above embodiments,
Various other variations are possible.

〔Effect of the invention〕

As described above, according to the present invention, the reed switch is provided with a constant current circuit that flows a constant current, and the filter circuit and the output transistor are connected between the power supply side of the reed switch and the load. Accordingly, power can be supplied to the load via the output transistor that responds to opening and closing of the reed switch, and therefore, the reed switch can be driven in a constant current circuit regardless of the size and type of the load. As a result, reed switch welding,
It has the effect of completely preventing problems such as melting and carbonization.

[Brief explanation of the drawing]

Fig. 1 is a cylinder piston position detection circuit diagram according to the present invention, Fig. 2 is a time chart of signal waveforms of various parts of the circuit shown in Fig. 1, and Fig. 3 shows another embodiment in more detail than Fig. 1. FIG. 4 is a circuit diagram showing another embodiment. ■...Sensor section, 2...Output circuit section, 3...Reed switch, 4...Constant current circuit, 5...Filter circuit, 6... ... Buffer amplifier, 7 ... Output transistor, 8 ... Light emitting diode, 9 ... Diode, 11 ... Stabilized power supply circuit, 12 ... Capacitor , 13... Current limiting resistor, 14... Resistor, 15... Capacitor, 16... Resistor, 17.18... Buffer amplifier, 19.20... Resistor, 21... Zener diode, 21a... Current limiting resistor, 22... Light emitting diode, 23... Resistor, 24... Zener diode.

Claims (1)

[Claims] This cylinder piston position detection circuit detects the position of a piston moving within a cylinder using a reed switch provided on the outer periphery of the cylinder, and supplies or cuts off power to a load by opening and closing the reed switch. and a filter circuit that has a constant current circuit that flows an appropriate constant current while the reed switch is in operation, and that absorbs chattering when the reed switch is opened and closed between the power supply side of the reed switch and the load, and this filter. A piston position detection circuit for a cylinder, characterized in that an output transistor is connected to control power supply to the load based on the output of the circuit.