JP6553103B2 - Fluid pressure cylinder sensor - Google Patents

Description

  The present invention relates to a sensor for fluid pressure cylinders.

  Conventionally, a fluid pressure cylinder using fluid pressure such as an air cylinder is known. Further, as a device for detecting the position of the piston of the fluid pressure cylinder, there is a sensor for fluid pressure cylinder having a two-wire sensor circuit configuration or the like. For example, an external load such as a programmable controller input card and an external power source are connected to such a fluid pressure cylinder sensor. The fluid pressure cylinder sensor is supplied with electric power from an external power source regardless of whether the fluid pressure cylinder sensor is ON or OFF.

  Further, as shown in FIG. 8, as an example of a fluid pressure cylinder sensor, a fluid pressure cylinder sensor 100 described in Patent Document 1 includes a bridge circuit 101 having magnetoresistive elements 101 a and 101 b and voltage dividing resistors 101 c and 101 d. And a comparator 102 to which an output signal from the bridge circuit 101 is input. In the fluid pressure cylinder sensor 100, the first transistor 111 whose output is input to the base terminal of the comparator 102, the light emitting diode 112 whose cathode terminal is connected to the collector terminal of the first transistor 111, and the light emitting diode 112 And a second transistor 113 having a base terminal connected to the anode terminal. The fluid pressure cylinder sensor 100 is used by being connected to an external load 121 and an external power source 122. In such a configuration, when the fluid pressure cylinder sensor 100 is ON, the voltage drop δV1 between the emitter and the base of the second transistor 113, the voltage drop δVa of the light emitting diode 19, and the collector-emitter of the first transistor 111. A drive voltage Vd obtained by combining the voltage drop amount .delta.V3 with the voltage drop amount .DELTA.V3 is applied to the bridge circuit 101.

JP 2007-139130 A

  Here, as shown in FIG. 9, a plurality of hydraulic cylinder sensors 100 and a plurality of hydraulic cylinders 110 may be incorporated into the automatic machine 200. In this case, it is assumed that the next sequence control is performed by the programmable controller based on the fluid pressure cylinder sensors 100 being turned on.

  For example, as shown in FIG. 10, a plurality of fluid pressure cylinder sensors 100 are connected in series as an example of a system for realizing the above usage mode, and an input card of a programmable controller, etc. A system is conceivable in which the external load 121 of and the external power supply 122 are connected. According to such a configuration, for example, when all of the fluid pressure cylinder sensors 100 are turned on, a current flows through the external load 121, so that all the fluid pressure cylinder sensors 100 are turned on to the external load 121. Can be detected.

  In the system as described above, the number N of fluid pressure cylinder sensors 100 that can be connected in series is determined by the minimum operating voltage Vmin of the external load 121, the power supply voltage V0 of the external power supply 122, and the drive voltage Vd. Specifically, since the value obtained by multiplying the drive voltage Vd by the number N of the fluid pressure cylinder sensors 100 needs to be set to be equal to or less than the value obtained by subtracting the minimum operating voltage Vmin from the power supply voltage V0, the fluid pressure The number N of cylinder sensors 100 is a natural number that satisfies the inequality N ≦ (V0−Vmin) / Vd. For this reason, the number N of fluid pressure cylinder sensors 100 that can be connected in series is limited.

  According to the above inequality, the number N can be increased by lowering the drive voltage Vd. Here, there is a concern that if the drive voltage Vd is lowered, the operation of the MR sensor package 103 becomes unstable. However, since the minimum operation voltage of the MR sensor package 103 has been lowered in recent years, the drive voltage Vd is lowered. The MR sensor package 103 can operate normally even under the above conditions.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a fluid pressure cylinder sensor capable of reducing the drive voltage applied to the bridge circuit when the fluid pressure cylinder sensor is ON. It is to be.

  A sensor for a fluid pressure cylinder which achieves the above object includes a bridge circuit including a magnetoresistive element, a comparator to which an output signal from the bridge circuit is input, a signal terminal and a common terminal, and a piston of the fluid pressure cylinder Two-wire sensor circuit configuration used for detecting the position of the first transistor, the first transistor whose output is input to the base terminal, and the base connected to the collector terminal of the first transistor via a connection line. A second transistor having a terminal, an emitter terminal connected to the signal terminal, and a collector terminal connected to the bridge circuit; a voltage regulating diode provided on the connection line and configured by a switching diode or a rectifier diode; When the first transistor and the second transistor are in the ON state, the second And a light emitting diode to which a voltage corresponding to the voltage drop between the emitter and the base of the resistor and the voltage drop of the voltage adjustment diode is applied, wherein the fluid pressure cylinder sensor comprises the first transistor and the second transistor. When the transistor is in an ON state, a drive voltage including the voltage drop amount between the emitter and base of the second transistor and the voltage drop amount of the voltage adjustment diode is applied to the bridge circuit. It is characterized by

  According to this configuration, when the first transistor and the second transistor are in the ON state, a voltage corresponding to the voltage drop between the emitter and the base of the second transistor and the voltage drop of the voltage adjustment diode is applied to the light emitting diode As a result, the light emitting diode emits light, and a drive voltage is applied to the bridge circuit. The driving voltage includes the voltage drop between the emitter and the base of the second transistor and the voltage drop of the voltage adjustment diode, but does not include the voltage drop of the light emitting diode. As a result, the drive voltage can be reduced as compared with the configuration in which the drive voltage includes the emitter-base voltage drop amount of the second transistor and the light-emitting diode voltage drop amount.

Regarding the fluid pressure cylinder sensor, the bridge circuit and the comparator may be incorporated in one package.
According to this configuration, the assembly of the fluid pressure cylinder sensor can be facilitated as compared with the case where the bridge circuit and the comparator are independent components.

  The fluid pressure cylinder sensor includes a bypass line connecting an emitter terminal or a collector terminal of the second transistor and a portion of the connection line between the first transistor and the voltage adjustment diode, the light emitting diode Is preferably provided on the bypass line.

  According to this configuration, since the light emitting diode is connected in parallel with the emitter-base of the second transistor and the voltage adjustment diode, the light emitting diode and the emitter-base of the second transistor are connected in series. It can suppress that a drive voltage becomes high resulting from the problem.

  In particular, according to this configuration, when the first transistor is turned on, current flows in both the voltage adjusting diode and the light emitting diode. Thus, current can flow through both the voltage adjustment diode and the light emitting diode connected in parallel with one transistor, so that the configuration can be simplified.

  A line connected to the signal terminal and the common terminal for the fluid pressure cylinder sensor, the bypass line being provided separately from a line passing through the voltage adjustment diode and the first transistor, and the bypass line And a third transistor that receives the output of the comparator to a base terminal. The light emitting diode may be provided on the bypass line.

  According to this configuration, the light emitting diode is connected in parallel to the emitter-base of the second transistor and to the voltage adjustment diode. Then, when the first transistor is turned on, the second transistor is turned on, and a drive voltage is applied to the bridge circuit. Further, when the third transistor is turned on, a voltage corresponding to the voltage drop between the emitter and base of the second transistor and the voltage drop of the voltage adjusting diode is applied to the light emitting diode. Accordingly, it is possible to suppress an increase in drive voltage due to the light emitting diode and the emitter-base of the second transistor being connected in series. In particular, according to this configuration, since the current is divided into the first transistor and the third transistor, the current amplification factor required for the first transistor and the third transistor can be reduced.

  In the fluid pressure cylinder sensor, a resistor may be provided on the bypass line to adjust a ratio between the current flowing through the voltage adjustment diode and the current flowing through the light emitting diode.

According to this configuration, the current flowing to the light emitting diode can be adjusted by the resistance. This can suppress, for example, excessive current flow to the light emitting diode.
The fluid pressure cylinder sensor may include a constant current circuit used to apply a voltage to the bridge circuit when the first transistor and the second transistor are in the OFF state.

  According to such a configuration, a voltage is applied to the bridge circuit even when the first transistor and the second transistor are in the OFF state. In addition, since the current flowing in the bridge circuit is constant by the constant current circuit, stable operation of the bridge circuit and the comparator can be realized in the situation where the first transistor and the second transistor are in the OFF state.

  In the fluid pressure cylinder sensor, the number of the voltage adjustment diodes is obtained by subtracting the voltage drop amount between the emitter and base of the second transistor from the voltage drop amount of the light emitting diode. It may be a quotient when divided by the amount of voltage drop per unit.

  According to this configuration, the voltage obtained by combining the voltage drop amount between the emitter and the base of the second transistor and the voltage drop amount of the voltage adjustment diode can be made close to the voltage drop amount of the light emitting diode. Thereby, the above-described effect can be realized with the minimum number of voltage adjustment diodes.

  According to the present invention, it is possible to reduce the drive voltage applied to the bridge circuit when the fluid pressure cylinder sensor is turned on.

FIG. 2 is a schematic perspective view of an air cylinder. The schematic diagram which shows the relationship between an air cylinder and a cylinder switch. The circuit diagram of the cylinder switch of 1st Embodiment. The circuit diagram of the cylinder switch of 2nd Embodiment. The circuit diagram of another example cylinder switch. The circuit diagram of another example cylinder switch. The circuit diagram of another example cylinder switch. The circuit diagram of a cylinder switch of a prior art. BRIEF DESCRIPTION OF THE DRAWINGS The conceptual diagram which shows an example of an automatic machine apparatus typically. FIG. 2 is a conceptual view schematically showing an electrical configuration of a cylinder switch.

First Embodiment
Hereinafter, a first embodiment of the fluid pressure cylinder sensor will be described.
A cylinder switch as a fluid pressure cylinder sensor is used to detect the position of the piston of an air cylinder, which is a type of fluid pressure cylinder. As shown in FIG. 1, the cylinder switch 11 is installed in a mounting groove 14 formed on the outer peripheral surface of the air cylinder 12 so as to extend along the moving direction of the piston rod 13 a. As shown in FIG. 2, a magnet 16 is provided in the housing groove 15 formed on the outer peripheral surface of the piston 13, and the cylinder switch 11 emits an output signal when the magnet 16 moves to a predetermined position with the piston 13. Is configured as. Although not shown, the mounting groove 14 is provided on the other surface of the air cylinder 12 in order to change the mounting position of the cylinder switch 11 appropriately.

  As shown in FIG. 2, the cylinder switch 11 includes various electronic components. These electronic components are all surface mounted components (SMD), and are mounted on the circuit board 17 to form a two-wire sensor circuit described later. An MR sensor package 18 as an electronic component, a light emitting diode 19 and electronic components such as transistors and resistors (not shown) are surface-mounted on the circuit board 17 by soldering. The various electronic components and the circuit board 17 are housed in the case 21.

Next, the circuit configuration of the cylinder switch 11 will be described based on FIG.
As shown in FIG. 3, the two-wire sensor circuit 22 constituting the cylinder switch 11 includes a bridge circuit 23 including magnetic resistance elements 23 a and 23 b and a comparator (op-amp) to which an output signal from the bridge circuit 23 is input. A signal terminal 25 and a common terminal 26 are provided.

  The bridge circuit 23 is composed of two magnetoresistance elements 23a and 23b and two voltage dividing resistors 23c and 23d. The connection point between the two magnetoresistive elements 23a and 23b is connected to the inverting input terminal of the comparator 24, and a magnetic detection signal is input to the comparator 24. The connection point between the two voltage dividing resistors 23c and 23d A reference voltage is input to the comparator 24 by being connected to the input terminal. The comparator 24 compares the output signal from the bridge circuit 23, binarizes High / Low, amplifies and outputs it. The bridge circuit 23 and the comparator 24 are incorporated into one package to form an MR sensor package 18.

  The two-wire sensor circuit 22 of the cylinder switch 11 has a first bus LN1 connecting the signal terminal 25 and the MR sensor package 18 (specifically, the bridge circuit 23), a common terminal 26, and the MR sensor package 18 (specifically, And a second bus LN2 for connecting to the bridge circuit 23).

  The two-wire sensor circuit 22 includes a first transistor 28 and a second transistor 29, a connection line LN3, and switching diodes 31 and 32 as voltage adjustment diodes.

  The first transistor 28 is an NPN transistor. The output terminal of the comparator 24 of the MR sensor package 18 is connected to the base terminal of the first transistor 28 via the resistor 27. That is, the output of the comparator 24 is input to the base terminal of the first transistor 28. The emitter terminal of the first transistor 28 is connected to the second bus LN2.

  The second transistor 29 is a PNP transistor. The second transistor 29 is provided on the first bus LN1, the emitter terminal of the second transistor 29 is connected to the signal terminal 25, and the collector terminal of the second transistor 29 is connected to the MR sensor package 18 (in detail). It is connected to the bridge circuit 23).

The connection line LN3 connects the collector terminal of the first transistor 28 and the base terminal of the second transistor 29.
The switching diodes 31 and 32 are provided on the connection line LN3. In the present embodiment, two switching diodes 31 and 32 are provided. Both the switching diodes 31 and 32 are connected in series with each other with the direction from the base terminal of the second transistor 29 toward the collector terminal of the first transistor 28 as the forward direction.

  According to such a configuration, when the first transistor 28 is in the ON state, the second transistor 29 is in the ON state, whereby the drive voltage Vd is applied to the MR sensor package 18 (bridge circuit 23).

  In this case, the diode characteristic between the emitter and the base of the second transistor 29 causes a voltage drop between the emitter and the base of the second transistor 29 and a voltage drop between both switching diodes 31 and 32. Therefore, the drive voltage Vd includes a first voltage drop amount δV1 that is a voltage drop amount between the emitter and the base of the second transistor 29, and a second voltage drop amount δV2 that is a voltage drop amount of both the switching diodes 31 and 32. including. Specifically, the drive voltage Vd is a combination of the first voltage drop amount δV1, the second voltage drop amount δV2, and the third voltage drop amount δV3 that is the collector-emitter voltage drop amount of the first transistor 28. Voltage. The drive voltage Vd is set to the minimum operating voltage (for example, 1.6 V) of the MR sensor package 18 or more.

  The two-wire sensor circuit 22 of the cylinder switch 11 includes a bypass line LN4 provided separately from the connection line LN3, and a light emitting diode 19 and a resistor 20 provided on the bypass line LN4.

  The bypass line LN4 is a portion connecting the emitter terminal of the second transistor 29 and the switching diodes 31 and 32 (specifically, the second switching diode 32) of the connection line LN3 and the collector terminal of the first transistor 28. And connected.

  The light emitting diode 19 and the resistor 20 are connected in series with each other on the bypass line LN4. The light emitting diode 19 and the resistor 20 are connected between the emitter and base of the second transistor 29 and in parallel with the switching diodes 31 and 32. For this reason, when both transistors 28 and 29 are in the ON state, a voltage corresponding to the voltage drop between the emitter and base of the second transistor 29 and the voltage drop of the switching diodes 31 and 32 is applied to the light emitting diode 19. The Specifically, a voltage obtained by combining the first voltage drop amount δV1 and the second voltage drop amount δV2 is applied to the series connection body of the light emitting diode 19 and the resistor 20. Incidentally, the voltage drop amount δVa of the light emitting diode 19 is larger than the voltage drop amount per switching diode 31, 32, and is larger than the second voltage drop amount δV2.

  The resistor 20 adjusts the ratio between the current flowing through the switching diodes 31 and 32 and the current flowing through the light emitting diode 19. Specifically, the magnitude relationship between the voltage applied to the series connection body composed of the light emitting diode 19 and the resistor 20 and the voltage obtained by combining the first voltage drop amount δV1 and the second voltage drop amount δV2 is the resistance value of the resistor 20. It changes accordingly, which changes the ratio of the two currents.

  In the present embodiment, the resistance value of the resistor 20 is a voltage obtained by combining the voltage drop amount δVa of the light emitting diode 19 and the voltage applied to the resistor 20 with the first voltage drop amount δV1 and the second voltage drop amount δV2. It is set to match. Specifically, a voltage (δV1 + δV2−δVa) obtained by subtracting the voltage drop amount δVa of the light emitting diode 19 from the voltage obtained by adding the first voltage drop amount δV1 and the second voltage drop amount δV2 is applied to the resistor 20. The resistance value of the resistor 20 is set.

  As shown in FIG. 3, the two-wire sensor circuit 22 of the cylinder switch 11 includes a constant current circuit 30 that is used to apply a voltage to the MR sensor package 18 when the cylinder switch 11 is OFF.

  The constant current circuit 30 is connected between the emitter and collector of the second transistor 29. The constant current circuit 30 includes a circuit in which a first constant current resistor R1 is connected between the collector and base of the NPN transistor Q1, and the collector terminal of the NPN transistor Q1 is connected to the emitter terminal of the second transistor 29. Yes. The first constant current resistor R1 has a resistance value that enables operation in a state where the NPN transistor Q1 is saturated. The constant current circuit 30 further includes a second constant current resistor R2 having one end connected to the emitter terminal of the NPN transistor Q1, a collector terminal connected to the base terminal of the NPN transistor Q1, and a base terminal connected to the NPN transistor Q1. And a second NPN transistor Q2 connected to the emitter terminal. The other end of the second constant current resistor R 2 and the emitter terminal of the second NPN transistor Q 2 are connected to the collector terminal of the second transistor 29.

  By setting the resistance values of the first constant current resistor R1 and the second constant current resistor R2 within a predetermined range, the current value flowing from the constant current circuit 30 to the MR sensor package 18 when the cylinder switch 11 is OFF is , And the cylinder switch 11 falls within a predetermined range that does not malfunction. For example, by setting the resistance value of the first constant current resistor R1 to 1 kΩ and the resistance value of the second constant current resistor R2 to 100 kΩ, the value of the current flowing through the MR sensor package 18 can be less than 1 mA. .

Further, between the signal terminal 25 and the common terminal 26, a Zener diode 33 for preventing a surge voltage and a capacitor 34 for preventing an external noise are connected in parallel.
The cylinder switch 11 is attached to a predetermined position of the air cylinder 12. For example, when the piston rod 13a is in a predetermined immersion state (reference position), an output signal of High is output from the MR sensor package 18 (comparator 24) by the action of the magnet 16, and the MR sensor is moved in the state of moving from the reference position. A low output signal is output from the package 18.

  As shown in FIG. 3, when one cylinder switch 11 is used, the cylinder switch 11 is connected between the external load 35 and the DC external power supply 36 between the signal terminal 25 of the two-wire sensor circuit 22 and the common terminal 26. Is used in the connected state. In this case, the + terminal of the external power supply 36 is connected to the signal terminal 25 via the external load 35, and the − terminal of the external power supply 36 is connected to the common terminal 26.

  When the cylinder switch 11 is turned on, that is, the piston rod 13a moves to the reference position and the MR sensor package 18 outputs a High output signal by the action of the magnet 16, the first transistor 28 is turned on. Then, the second transistor 29 is turned on, and from the signal terminal 25, between the emitter and base of the second transistor 29, both the switching diodes 31 and 32 of the connection line LN3, and between the collector and emitter of the first transistor 28. The current for operating the external load 35 flows to the common terminal 26 through the first current path EL1 which passes through. Then, the drive voltage Vd is applied to the MR sensor package 18.

  Further, when both transistors 28 and 29 are turned on, a current flows through the second current path EL2 passing through the light emitting diode 19 and resistor 20 of the bypass line LN4 and between the collector and emitter of the first transistor 28. . Thereby, it can be visually confirmed that the light emitting diode 19 is turned on and the cylinder switch 11 is turned on. That is, the cylinder switch 11 is provided separately from the first current path EL1 flowing between the emitter-base of the second transistor 29 and between the switching diodes 31 and 32, and the first current path EL1. It can be said that a current path EL2 is provided. The first current path EL1 and the second current path EL2 are common to a part (first transistor 28).

  In the present embodiment, the current flowing between the emitter and the base of the second transistor 29 is different from the current flowing through the light emitting diode 19. As already described, the ratio of the current flowing through the switching diodes 31 and 32 and the current flowing through the light emitting diode 19 is adjusted by the resistor 20 on the bypass line LN4. As a result, the current flowing through the light emitting diode 19 is It is lower than the rated current of the light emitting diode 19. That is, the resistor 20 limits the current flowing through the light emitting diode 19 to be lower than the rated current by adjusting the ratio of the current flowing through the switching diodes 31 and 32 and the current flowing through the light emitting diode 19. It is functioning.

  Incidentally, the second transistor 29 contributes to stable operation of the MR sensor package 18 by being turned on when the cylinder switch 11 is turned on. More specifically, if the second transistor 29 does not exist and the constant current circuit 30 is provided on the first bus LN1, the voltage divided by the constant current circuit 30 is applied to the MR sensor package 18. It will be done. In this case, the voltage applied to the MR sensor package 18 is lowered, and the operation of the MR sensor package 18 may become unstable.

  In this respect, in the present embodiment, since the second transistor 29 is provided on the first bus LN 1 and the constant current circuit 30 is provided in parallel with the second transistor 29, the second transistor 29 is provided. When in the ON state, the voltage (drive voltage Vd) applied to the MR sensor package 18 is not divided by the constant current circuit 30. As a result, it is possible to suppress the disadvantage caused by the constant current circuit 30, that is, the decrease in the voltage applied to the MR sensor package 18 due to the partial pressure.

  The second transistor 29 is turned off when the cylinder switch 11 is turned off, thereby restricting the flow of current to the MR sensor package 18 through the first bus LN 1, thereby making the constant current circuit 30 effective. It makes it function.

  The external load 35 includes, for example, a photocoupler. When a current flows through the external load 35, the photocoupler is turned on, and a signal is output to the programmable controller. The programmable controller executes sequence control by the input of the signal.

Next, the operation of this embodiment will be described.
When the cylinder switch 11 is ON, that is, when the output signal from the comparator 24 is High, the drive voltage Vd is applied to the MR sensor package 18, and the first voltage drop amount δV1 and the second voltage drop amount δV2 The combined voltage is applied to the light emitting diode 19 and the resistor 20.

  Here, the drive voltage Vd is lower than the voltage obtained by combining the first voltage drop amount δV1 and the voltage drop amount δVa of the light emitting diode 19. For this reason, the drive voltage Vd is lower than that of the configuration shown in FIG. 8, that is, the configuration in which the light emitting diode 19 is connected in series with the emitter-base of the second transistor 29.

  For example, it is assumed that the voltage drop amount δVa of the light emitting diode 19 is 2.0V, the first voltage drop amount δV1 is 0.7V, and the third voltage drop amount δV3 is 0.1V. Further, assuming that the amount of voltage drop per switching diode 31 or 32 is 0.7 V, the second amount of voltage drop ΔV2 is 1.4 V. In this case, the drive voltage Vd applied to the MR sensor package 18 is 2.2V (= 0.7V + 1.4V + 0.1V).

  The driving voltage Vd in the fluid pressure cylinder sensor 100 of FIG. 8 shown as a comparison target is the sum of the voltage drop amount δVa of the light emitting diode 19, the first voltage drop amount δV1, and the third voltage drop amount δV3. It is 2.8V. For this reason, the drive voltage Vd can be reduced by 0.6 V under the above conditions.

  In addition, since the combined voltage of the first voltage drop amount δV1 and the second voltage drop amount δV2 is 2.1 V and the voltage drop amount δVa of the light emitting diode 19 is 2.0 V, the resistance value of the resistor 20 is The resistance 20 is set to be applied with 0.1 V (= 2.1 V-2.0 V). Thereby, the same current flows to the light emitting diode 19 and both the switching diodes 31 and 32.

  As a specific example, a model DSA5002 (manufactured by Panasonic) was used as the second transistor 29, a model 1SS400 (manufactured by ROHM) was used as the switching diodes 31 and 32, and a model 2SC4154 (manufactured by Isahaya Electronics Co., Ltd.) was employed as the light emitting diode 19. Then, the resistance value of the resistor 20 was set to 20Ω, the external load 35 was set to 1 kΩ, and the power supply voltage V0 was actually measured to 24V. In this case, when the cylinder switch 11 is ON, a current of about 20 mA flows through the MR sensor package 18, and the drive voltage Vd (specifically, the voltage between both terminals 25 and 26 when the cylinder switch 11 is ON) is 2.2V. Met.

  Next, the case where a plurality of cylinder switches 11 are used will be described. As a mode of use in which a plurality of cylinder switches 11 are used, for example, it is assumed that the plurality of cylinder switches 11 are connected in series to the external load 35 and the external power supply 36. In detail, the signal terminal 25 of the cylinder switch 11 located on the most upstream side is connected to the + terminal of the external power supply 36 via the external load 35, and the common terminal 26 of the cylinder switch 11 located on the most downstream side is the − terminal of the external power supply 36 Connected to. The common terminal 26 of the upstream cylinder switch 11 and the signal terminal 25 of the downstream cylinder switch 11 are connected to each other.

  The number N of cylinder switches 11 that can be connected in series to the external power source 36 when the cylinder switches 11 are connected in series as described above will be described. If the minimum operating voltage Vmin of the external load 35 is 10 V and the power supply voltage V0 is 24 V, in this embodiment, the number N of cylinder switches 11 that can be connected in series is N ≦ (V0−Vmin) / Vd. Because it is a natural number that satisfies the inequality, it becomes "6". On the other hand, the number N that can be connected in series in the fluid pressure cylinder sensor 100 to be compared is “5”.

According to the embodiment described above, the following effects can be obtained.
(1-1) The cylinder switch 11 of the two-wire sensor circuit configuration used to detect the position of the piston 13 of the air cylinder 12 has a bridge circuit 23 including magnetoresistive elements 23a and 23b and an output signal from the bridge circuit 23 Are input, and the signal terminal 25 and the common terminal 26 are provided. The cylinder switch 11 has a first transistor 28 whose output receives the output of the comparator 24 at its base terminal, and a second transistor 29 having its base terminal connected to the collector terminal of the first transistor 28 via the connection line LN3. And. The collector terminal of the second transistor 29 is connected to the bridge circuit 23, and the emitter terminal of the second transistor 29 is connected to the signal terminal 25.

  In such a configuration, the cylinder switch 11 is provided with the switching diodes 31 and 32 provided on the connection line LN 3 and the voltage drop between the emitter and the base of the second transistor 29 when both the transistors 28 and 29 are in the ON state. And a light emitting diode 19 to which a voltage corresponding to the voltage drop of the switching diodes 31 and 32 is applied. When the both transistors 28 and 29 are in the ON state, the cylinder switch 11 has a first voltage drop δV1 that is a voltage drop between the emitter and base of the second transistor 29 and a voltage drop across the switching diodes 31 and 32. A drive voltage Vd including a second voltage drop amount δV2 which is an amount is applied to the bridge circuit 23.

  According to this configuration, the drive voltage Vd includes the first voltage drop amount δV1, but does not include the voltage drop amount δVa of the light emitting diode 19. As a result, the drive voltage Vd can be reduced as compared with a configuration in which the first voltage drop amount δV1 and the voltage drop amount δVa of the light emitting diode 19 are included in the drive voltage Vd. Therefore, the number N of cylinder switches 11 that can be connected in series can be increased.

  Further, since the switching diodes 31 and 32 that cause a certain amount of voltage drop are provided on the connection line LN3, a voltage corresponding to the voltage drop amount δVa of the light emitting diode 19 can be applied to the light emitting diode 19. .

  Here, focusing on the point of causing a voltage drop, it may be considered to provide a Schottky barrier diode or a zener diode, for example, instead of the switching diodes 31 and 32. However, in general, the voltage drop amount of the Schottky barrier diode is sufficiently smaller than the voltage drop amount δVa of the light emitting diode 19, so that the number of Schottky barrier diodes tends to increase and there is a concern that the number of components increases. . On the other hand, the voltage drop amount of the Zener diode is generally not suitable for use because it tends to be larger than the voltage drop amount δVa of the light emitting diode 19.

  In this regard, in this embodiment, the switching diodes 31 and 32 are employed as elements that cause a certain amount of voltage drop. The voltage drop amount of the switching diodes 31 and 32 is large compared to the voltage drop amount of the Schottky barrier diode and tends to be smaller than the voltage drop amount of the zener diode. Thereby, the voltage necessary for light emission can be applied to the light emitting diode 19 while reducing the number of parts.

  (1-2) The voltage drop amount δVa of the light emitting diode 19 is larger than the voltage drop amount per switching diode 31, 32. In such a configuration, two switching diodes 31 and 32 are provided. According to such a configuration, the voltage obtained by combining the first voltage drop amount δV1 and the second voltage drop amount δV2 that is the voltage drop amount of both the switching diodes 31 and 32 can be brought close to the voltage drop amount δVa of the light emitting diode 19. it can.

  (1-3) The cylinder switch 11 includes a bypass line LN4 that connects the emitter terminal of the second transistor 29 and a portion of the connection line LN3 between the first transistor 28 and the switching diodes 31 and 32. . The light emitting diode 19 is provided on the bypass line LN4.

  According to this configuration, since the light emitting diode 19 is connected between the emitter-base of the second transistor 29 and in parallel with the switching diodes 31 and 32, the distance between the light emitting diode 19 and the emitter-base of the second transistor 29 is It is possible to suppress that the drive voltage Vd becomes high due to the series connection of

  In particular, in the present embodiment, when the first transistor 28 is turned ON, current flows in both the switching diodes 31 and 32 and the light emitting diode 19. As a result, both currents can be supplied by one transistor, and the structure can be simplified.

  (1-4) On the bypass line LN4, there is provided a resistor 20 that adjusts the ratio of the current flowing through the switching diodes 31 and 32 and the current flowing through the light emitting diode 19. According to this configuration, the current flowing through the light emitting diode 19 can be adjusted by the resistor 20. Thus, by adjusting the resistance value of the resistor 20, for example, it is possible to suppress the flow of an excessive current (for example, a current higher than the rated current) in the light emitting diode 19. In other words, a current equal to or greater than the rated current of the light emitting diode 19 can be supplied to the cylinder switch 11 (in other words, the external load 35).

  In particular, in the present embodiment, the resistance value of the resistor 20 is the sum of the voltage drop amount δVa of the light emitting diode 19 and the voltage applied to the resistor, and the sum of the first voltage drop amount δV1 and the second voltage drop amount δV2. It is set to the same voltage as the As a result, the current flowing through the cylinder switch 11 (specifically, the current flowing through the cylinder switch 11 excluding the current flowing through the MR sensor package 18) It is equally divided into the current flow. Thus, an appropriate current can be supplied to the light emitting diode 19.

  (1-5) The cylinder switch 11 uses the constant current circuit 30 used to apply a voltage to the MR sensor package 18 (specifically, the bridge circuit 23) in a state where both the transistors 28 and 29 are in the OFF state. I have. According to such a configuration, a voltage is applied to the MR sensor package 18 even when both transistors 28 and 29 are in the OFF state. Further, since the current flowing through the MR sensor package 18 is constant by the constant current circuit 30, stable operation of the MR sensor package 18 can be realized in a situation where both the transistors 28 and 29 are in the OFF state.

  (1-6) The bridge circuit 23 and the comparator 24 are incorporated in one package as the MR sensor package 18. According to such a configuration, the cylinder switch 11 can be easily assembled as compared with the case where the bridge circuit 23 and the comparator 24 are independent parts.

Second Embodiment
In the present embodiment, as shown in FIG. 4, the cylinder switch 11 includes a bypass line LN 14 connected to the signal terminal 25 and the common terminal 26.

  The bypass line LN14 is connected to a first bus LN1 connected to the signal terminal 25 and a second bus LN2 connected to the common terminal 26. In the present embodiment, the bypass line LN14 is provided on both terminals 25 and 26 side with respect to the series connection body of the switching diodes 31 and 32 and the first transistor 28. Specifically, the bypass line LN14 is connected to a portion connecting the signal terminal 25 and the emitter terminal of the second transistor 29 in the first bus LN1, and is connected to the emitter terminal of the first transistor 28 in the second bus LN2. It is connected to the part by the side of the common terminal 26 rather than the connection point P of this. The bypass line LN14 is provided separately from the line passing through the switching diodes 31, 32 and the first transistor 28.

  A resistor 20, a light emitting diode 19, and a third transistor 38 are provided on the bypass line LN14. The resistor 20, the light emitting diode 19 and the third transistor 38 are connected in series with one another, and the series connection of these is connected in parallel with both the switching diodes 31, 32 and the first transistor 28. .

The light emitting diode 19 is provided on the bypass line LN14 with the direction from the first bus LN1 to the second bus LN2 as the forward direction.
The third transistor 38 has a collector terminal connected to the cathode terminal of the light emitting diode 19 and an emitter terminal connected to the second bus LN2. The third transistor 38 has a base terminal connected to the comparator 24 via a resistor 37. The output of the comparator 24 is input to both the first transistor 28 and the third transistor 38. That is, the first transistor 28 and the third transistor 38 are synchronized. In the present embodiment, the third transistor 38 is the same type as the first transistor 28.

The operation of this embodiment will be described.
When a high output signal is output from the comparator 24, the first transistor 28 and the third transistor 38 are turned on. As a result, the drive voltage Vd is applied to the MR sensor package 18, and the drive voltage Vd is also applied to the series connected body composed of the resistor 20, the light emitting diode 19 and the third transistor 38. Therefore, a current flows through the first current path EL1, and a current flows through the bypass line LN14. In this case, a voltage corresponding to the first voltage drop amount δV1 and the second voltage drop amount δV2, more specifically, a voltage corresponding to the voltage drop amount δVa of the light emitting diode 19 is applied to the light emitting diode 19. In the present embodiment, the bypass line LN14 constitutes a second current path EL2, and the first current path EL1 and the second current path EL2 are independent of each other.

According to the embodiment described above, the following effects can be obtained.
(2-1) A light emitting diode 19 and a third transistor 38 are provided on a bypass line LN14 provided separately from a line passing through both the switching diodes 31 and 32 and the first transistor 28. The third transistor 38 has a base terminal to which the output of the comparator 24 is input. Even in such a configuration, the effect (1-1) and the like are exhibited.

  In particular, in the present embodiment, the third transistor 38 is provided separately from the first transistor 28. As a result, the current flowing through the cylinder switch 11 is divided into the current flowing through the first transistor 28 and the current flowing through the third transistor 38. Therefore, a variety having a low current amplification factor can be adopted as the first transistor 28 and the third transistor 38.

  More specifically, in the first embodiment, a current obtained by combining the current flowing through the connection line LN3 and the current flowing through the bypass line LN4 flows through the first transistor 28. On the other hand, in this embodiment, since the current is shunted to the first transistor 28 and the third transistor 38, the current flowing to each transistor 28, 38 flows to the first transistor 28 of the first embodiment. It can be smaller than the current. As a result, the current amplification factor required for each of the transistors 28 and 38 may be small. Therefore, a type having a low current amplification factor can be adopted for each of the transistors 28 and 38.

The above embodiments may be modified as follows.
As shown in FIG. 5, in the first embodiment, the bypass line LN4 may connect the collector terminal of the second transistor 29 and the connection line LN3.

  Similarly, as shown in FIG. 6, in the second embodiment, the bypass line LN 14 may be provided between both the transistors 28 and 29 and the MR sensor package 18. Specifically, one end of the bypass line LN14 is connected to a portion connecting the collector terminal of the second transistor 29 and the MR sensor package 18 in the first bus LN1, and the other end of the bypass line LN14 is connected to the second bus LN2. Of these, the MR sensor package 18 side may be connected to the connection point P.

  The resistance value of the resistor 20 is such that the voltage obtained by combining the voltage applied to the resistor 20 and the voltage drop amount δVa of the light emitting diode 19 is greater than the voltage obtained by combining the first voltage drop amount δV1 and the second voltage drop amount δV2. Alternatively, it may be set to be smaller. Thus, the ratio between the current flowing through both switching diodes 31 and 32 and the current flowing through the light emitting diode 19 can be changed. In short, the resistance value of the resistor 20 is set corresponding to each voltage drop amount δV1, δV2, δVa so that a current that is greater than or equal to the minimum current that can be emitted by the light emitting diode 19 and less than the rated current flows to the light emitting diode 19. It is good to have.

  In the first embodiment, the number of switching diodes is not limited to two, and may be set based on the respective voltage drop amounts δV1, δV2, and δVa. For example, the number of switching diodes may be set so that the voltage obtained by adding the first voltage drop amount δV1 and the second voltage drop amount δV2 approaches the voltage drop amount δVa of the light emitting diode 19. Specifically, the number of switching diodes is set to a quotient when a value obtained by subtracting the first voltage drop amount δV1 from the voltage drop amount δVa of the light emitting diode 19 is divided by the voltage drop amount per switching diode. It is good to be done.

  Further, in the configuration in which the number of switching diodes is set as described above, if a remainder is generated in the division, the resistance value of the resistor 20 may be set so that the voltage of the remainder is applied. The resistor 20 may be omitted if the above remainder does not occur. That is, the resistor 20 is not essential. The same applies to the second embodiment.

  In place of the switching diodes 31 and 32, a rectifying diode may be used. In short, the voltage adjustment diode may be formed of a switching diode or a rectifier diode.

  As shown in FIG. 7, the cylinder switch 11 may be provided with a three-terminal regulator 40 as a constant voltage circuit instead of the constant current circuit 30. In this case, the three-terminal regulator 40 may be connected to the first bus LN1 and the second bus LN2 so as to apply a constant voltage to the MR sensor package 18.

The bridge circuit 23 and the comparator 24 may not be packaged.
The mounting position of the cylinder switch 11 with respect to the air cylinder 12 is not limited to the position where the piston 13 is detected in the state where the piston rod 13a is immersed. For example, it may be a position for detecting the piston 13 in a state in which the piston rod 13a protrudes, or a position for detecting the piston 13 in a state in which the piston rod 13a protrudes to a predetermined intermediate position.

The fluid pressure cylinder is not limited to the air cylinder 12 and may be a hydraulic cylinder that operates with hydraulic oil.
The fluid pressure cylinder to which the cylinder switch 11 is attached is not limited to a direct acting fluid pressure cylinder, and may be a rotary cylinder. In this case, the cylinder switch 11 may be used for position detection in the rotational direction of the shaft of the rotary cylinder.

The cylinder switch 11 may be used alone or in combination with each other in series.
The embodiments and other examples may be combined as appropriate.

Next, a preferable example that can be grasped from each of the above embodiments and other examples will be described below.
(A) A first bus connecting the bridge circuit and the signal terminal and a second bus connecting the bridge circuit and the common terminal are provided, and the emitter terminal of the first transistor is connected to the second bus, The second transistor may be provided on the first bus bar.

  (Ii) The resistance of the resistor is determined by combining the voltage drop of the light emitting diode and the voltage applied to the resistor with the voltage drop between the emitter and the base of the second transistor and the voltage drop of the voltage adjustment diode. It is good to be set to match the voltage.

  11: cylinder switch (sensor for fluid pressure cylinder), 13: piston, 18: MR sensor package, 19: light emitting diode, 20: resistance, 23: bridge circuit, 23a, 23b: magnetic resistance element, 24: comparator, 25 Signal terminal 26 Common terminal 28 First transistor 29 Second transistor 30 Constant current circuit 31, 32 Switching diode (voltage adjustment diode) 38 Third transistor LN1 First bus , LN2 ... second bus, LN3 ... connection line, LN4, LN14 ... bypass line, Vd ... drive voltage.

Claims (7)

Two-wire sensor circuit configuration including a bridge circuit including a magnetoresistive element, a comparator to which an output signal from the bridge circuit is input, a signal terminal and a common terminal, and used to detect the position of a piston of a fluid pressure cylinder A fluid pressure cylinder sensor,
A first transistor in which an output of the comparator is input to a base terminal;
A second transistor having a base terminal connected to the collector terminal of the first transistor via a connection line, an emitter terminal connected to the signal terminal, and a collector terminal connected to the bridge circuit;
A voltage adjusting diode provided on the connection line and configured by a switching diode or a rectifying diode;
A light emitting diode to which a voltage corresponding to the voltage drop between the emitter and the base of the second transistor and the voltage drop of the voltage adjustment diode is applied when the first transistor and the second transistor are in the ON state;
Equipped with
The fluid pressure cylinder sensor includes a voltage drop amount between the emitter and the base of the second transistor and a voltage drop amount of the voltage adjustment diode when the first transistor and the second transistor are in the ON state. A fluid pressure cylinder sensor, wherein a drive voltage is applied to the bridge circuit.   The sensor for a fluid pressure cylinder according to claim 1, wherein the bridge circuit and the comparator are integrated into one package. A bypass line connecting the emitter terminal or collector terminal of the second transistor and a portion of the connection line between the first transistor and the voltage regulation diode;
The fluid pressure cylinder sensor according to claim 1, wherein the light emitting diode is provided on the bypass line. A line connected to the signal terminal and the common terminal, the bypass line provided separately from a line passing through the voltage adjustment diode and the first transistor;
A third transistor provided on the bypass line, the output of the comparator being input to a base terminal;
Equipped with
The fluid pressure cylinder sensor according to claim 1, wherein the light emitting diode is provided on the bypass line.   5. The fluid pressure cylinder sensor according to claim 3, wherein a resistor for adjusting a ratio of a current flowing through the voltage adjustment diode and a current flowing through the light emitting diode is provided on the bypass line. 6.   The constant current circuit used for applying a voltage to the said bridge circuit in the condition where the said 1st transistor and the said 2nd transistor are OFF states are provided in any one of Claims 1-5. Sensor for fluid pressure cylinder.   The number of voltage regulation diodes is obtained by subtracting the voltage drop amount between the emitter and base of the second transistor from the voltage drop amount of the light emitting diode, and dividing the value by the voltage drop amount per one of the voltage regulation diodes. The fluid pressure cylinder sensor according to any one of claims 1 to 6, which is a quotient of time.

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