Fluid pressure cylinder

Abstract

The first MR sensor (28) and the second MR sensor (30) are composed of a first magnetoresistance effect element pattern and a second magnetoresistance effect element pattern. The first MR sensor and the second MR sensor are arranged at a predetermined interval (L) so that when the first MR sensor receives the most magnetic field component of the magnet (26) in a direction parallel to the axial direction of the piston (18), the second MR sensor receives the most magnetic field component of the magnet in a direction parallel to the radial direction of the piston.

Description

Technical Field

[0001] The present invention relates to a fluid pressure cylinder, and in particular to a fluid pressure cylinder provided with a position detection mechanism. Background Art

[0002] Conventionally, there is known a fluid pressure cylinder in which a magnet (permanent magnet) is mounted on a piston and a magnetic sensor for detecting the magnetic field of the magnet is provided in a cylinder tube to detect the position of the piston.

[0003] When such a fluid pressure cylinder is used in an environment where an external magnetic field exists, there is a possibility that the position of the piston may be erroneously detected due to the influence of the external magnetic field.

[0004] Japanese Utility Model Publication No. 4-59404 describes a position detection device for a fluid pressure actuating device that suppresses malfunctions caused by an external magnetic field. The position detection device is provided with a first detection sensor and a second detection sensor in the displacement direction of a piston having a built-in permanent magnet, and the influence of the external magnetic field is offset by subtracting the output of the first detection sensor from the output of the second detection sensor.

[0005] However, Japanese Utility Model Application Laid-Open No. 4-59404 only considers external magnetic fields such as the external magnetic field in a welding line, in which the magnetic field acting on the first detection sensor is the same as the magnetic field acting on the second detection sensor. It is desired to prevent a fluid pressure cylinder from erroneously detecting the position of a piston when various external magnetic fields act by using a simple magnetic sensor structure. Summary of the invention

[0006] The present invention has been made under the background of the above circumstances, and an object of the present invention is to provide a fluid pressure cylinder which effectively utilizes a magnetoresistive element and thereby does not erroneously detect the position of a piston even when various external magnetic fields act.

[0007] The fluid pressure cylinder of the present invention detects the presence of the piston at a predetermined position by detecting the magnetic field of the magnet installed on the piston through the first MR sensor and the second MR sensor installed on the cylinder tube, wherein the first MR sensor and the second MR sensor are composed of a first magnetoresistance effect element pattern and a second magnetoresistance effect element pattern, wherein the resistance value of the first magnetoresistance effect element pattern decreases in accordance with the strength of the magnetic field in the direction parallel to the axial direction of the piston, and the resistance value of the second magnetoresistance effect element pattern decreases in accordance with the strength of the magnetic field in the direction parallel to the radial direction of the piston. Furthermore, the first MR sensor and the second MR sensor are arranged at a predetermined interval so that when the first MR sensor receives the largest magnetic field component of the magnet in the direction parallel to the axial direction of the piston, the second MR sensor receives the largest magnetic field component of the magnet in the direction parallel to the radial direction of the piston.

[0008] In addition, the fluid pressure cylinder of the present invention can also detect the presence of the piston at a predetermined position by detecting the magnetic field of the magnet installed on the piston through the first MR sensor, the second MR sensor, and the third MR sensor installed on the cylinder tube. The first MR sensor, the second MR sensor, and the third MR sensor are composed of a first magnetoresistance effect element pattern and a second magnetoresistance effect element pattern, the resistance value of which decreases according to the strength of the magnetic field in the direction parallel to the axial direction of the piston, and the resistance value of which decreases according to the strength of the magnetic field in the direction parallel to the radial direction of the piston. In addition, the first MR sensor, the second MR sensor, and the third MR sensor are arranged at a predetermined interval in the direction parallel to the axial direction of the piston, so that when the first MR sensor receives the most magnetic field component of the magnet in the direction parallel to the axial direction of the piston, the second MR sensor and the third MR sensor receive the most magnetic field component of the magnet in the direction parallel to the radial direction of the piston.

[0009] According to the above-described fluid pressure cylinder, by effectively utilizing the function of the MR sensor, the position of the piston can be detected with high accuracy, and erroneous detection of the position of the piston can be prevented when various external magnetic fields act.

[0010] The fluid pressure cylinder of the present invention has a plurality of MR sensors having a pair of magnetoresistive effect element patterns that respond to two directions orthogonal to each other and are arranged at a predetermined interval, so that the position of the piston can be detected with good accuracy, and there is no need to worry about erroneous detection of the position of the piston even if various external magnetic fields act. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram of the fluid pressure cylinder according to the first embodiment of the present invention when it is located at a predetermined operating position.

[0012] Figure 2 It is represented by a schematic diagram Figure 1 FIG. 1 is a diagram showing a structure of an MR sensor included in a fluid pressure cylinder.

[0013] Figure 3 It is represented by a circuit diagram Figure 1 FIG. 1 is a diagram showing a structure of an MR sensor included in a fluid pressure cylinder.

[0014] Figure 4 yes Figure 1 Schematic diagram of the fluid pressure cylinder when it is in other action positions.

[0015] Figure 5 yes Figure 1 Schematic diagram of the fluid pressure cylinder when it is in another operating position.

[0016] Figure 6It means corresponding to Figure 1 A diagram of the output of the MR sensor of the position of the piston in the fluid pressure cylinder.

[0017] Figure 7 It is represented by a block diagram Figure 1 FIG. 1 is a diagram showing a structure of a sensor module included in a fluid pressure cylinder.

[0018] Figure 8 It means corresponding to Figure 1 A diagram of the output of a comparison unit etc. of the position of a piston in a fluid pressure cylinder.

[0019] Fig. 9 It means that the magnetic field of other fluid pressure cylinders acts on Figure 1 A diagram of what a fluid pressure cylinder looks like.

[0020] Fig.10 It is a diagram showing the output of the MR sensor based on the magnetic field of another fluid pressure cylinder.

[0021] Fig.11 It means the welding magnetic field in direction A acts on Figure 1 A diagram of what a fluid pressure cylinder looks like.

[0022] Fig.12 This is a diagram showing the output of the MR sensor based on the welding magnetic field in the A direction.

[0023] Fig.13 It means the welding magnetic field in the B direction acts on Figure 1 A diagram of what a fluid pressure cylinder looks like.

[0024] Fig.14 This is a diagram showing the output of the MR sensor based on the welding magnetic field in the B direction.

[0025] Fig.15 is the magnetic field of the magnetized bolt acting on Figure 1 A diagram of what a fluid pressure cylinder looks like.

[0026] Fig.16 FIG. 1 is a diagram showing the output of the MR sensor based on the magnetic field of the magnetized bolt.

[0027] Fig.17 This is a schematic diagram of a fluid pressure cylinder according to a second embodiment of the present invention when it is located at a predetermined operating position.

[0028] Fig.18 It means corresponding to Fig.17 A diagram of the output of the MR sensor of the position of the piston in the fluid pressure cylinder.

[0029] Fig.19 It is represented by a block diagram Fig.17FIG. 1 is a diagram showing a structure of a sensor module included in a fluid pressure cylinder.

[0030] Fig. 20 It means corresponding to Fig.17 A diagram of the output of a comparison unit etc. of the position of a piston in a fluid pressure cylinder. DETAILED DESCRIPTION

[0031] Hereinafter, a plurality of preferred embodiments of the fluid pressure cylinder of the present invention will be described with reference to the drawings.

[0032] (First Embodiment)

[0033] Reference Figures 1 to 16 , a fluid pressure cylinder 10 according to a first embodiment of the present invention will be described. Figure 1 As shown, the fluid pressure cylinder 10 includes: a cylinder 16 closed at one end by a rod cover 12 and at the other end by a head cover 14, a piston 18 slidably disposed in the cylinder 16, and a piston rod 20 connected to the piston 18. The cylinder 16, the rod cover 12, the head cover 14, the piston 18, and the piston rod 20 are all made of non-magnetic materials such as aluminum alloy.

[0034] In the following description, when words about up, down, left, and right directions are used, for convenience, they refer to directions in the drawings, and do not limit the actual arrangement of components, etc. In addition, the direction parallel to the axial direction of the piston 18 as the sliding direction of the piston 18, that is, the left and right direction in the drawings may be referred to as the A direction, and the direction parallel to the radial direction of the piston 18, that is, the up and down direction in the drawings may be referred to as the B direction.

[0035] The internal space of the cylinder 16 is divided into a first pressure chamber 22 on the rod cover 12 side and a second pressure chamber 24 on the head cover 14 side by the piston 18. The first pressure chamber 22 and the second pressure chamber 24 are respectively supplied with pressure fluid or discharged with pressure fluid via ports not shown. One end of the piston rod 20 is connected to the piston 18, and the other end of the piston rod 20 extends to the outside through the rod cover 12.

[0036] When pressure fluid is supplied to the first pressure chamber 22 and pressure fluid is discharged from the second pressure chamber 24, the piston 18 moves to the right, thereby pulling in the piston rod 20. When pressure fluid is supplied to the second pressure chamber 24 and pressure fluid is discharged from the first pressure chamber 22, the piston 18 moves to the left, thereby pushing out the piston rod 20.

[0037] In the present embodiment, the required work is performed in the pushing process of the piston rod 20. For example, in the welding line, the workpiece of the plate to be welded is positioned and held by the other end of the piston rod 20. In addition, the process of moving the piston 18 in the direction of pushing out the piston rod 20 is called a "driving process", and the process of moving the piston 18 in the direction of pulling in the piston rod 20 is called a "return process".

[0038] An annular magnet (permanent magnet) 26 is mounted on the outer periphery of the piston 18. The magnet 26 is magnetized in the A direction, with the left end face of the magnet 26 being the N pole and the right end face being the S pole. A magnetic field (magnetic flux) 46 is formed around the magnet 26, and the magnetic field 46 starts from the left end face of the magnet 26, passes through the radially outer side of the magnet 26, and returns to the right end face of the magnet 26. The magnetic field 46 extends across the cylinder 16 to a specified area. In the present embodiment, the shape of the magnet 26 is annular around the piston 18 at 360 degrees, but in the case of a structure that limits the rotation of the piston 18, the shape of the magnet 26 may not be annular.

[0039] On the outside of the cylinder 16 close to the rod cover 12, a first MR sensor 28 and a second MR sensor 30 are installed as magnetic sensors using magnetoresistive elements at a predetermined distance L in the A direction. In addition, a sensor module 32 is provided on the outside of the cylinder 16, and the sensor module 32 is connected to the first MR sensor 28 and the second MR sensor 30 and processes the outputs from these sensors. In the present embodiment, the first MR sensor 28 and the second MR sensor 30 are provided as separate bodies from the sensor module 32, but these sensors may also be assembled in the sensor module 32.

[0040] The first MR sensor 28 and the second MR sensor 30 have the same structure, and therefore, as a representative, refer to Figure 2 and Figure 3 The structure of the first MR sensor 28 will be described. Figure 2 As shown, the first MR sensor 28 is a combination of a first magnetoresistance effect element pattern 28a and a second magnetoresistance effect element pattern 28b, wherein the first magnetoresistance effect element pattern 28a responds to a magnetic field in a C direction so that the resistance value decreases according to its strength, and the second magnetoresistance effect element pattern 28b responds to a magnetic field in a D direction perpendicular to the C direction so that the resistance value decreases according to its strength.

[0041] like Figure 3As shown, one end of the first magnetoresistance effect element pattern 28a is connected to the positive power supply voltage (Vcc), and one end of the second magnetoresistance effect element pattern 28b is connected to the reference voltage (Gnd). The potential of the connection point between the first magnetoresistance effect element pattern 28a and the second magnetoresistance effect element pattern 28b is the output (V1) of the first MR sensor 28. When the resistance value of the first magnetoresistance effect element pattern 28a decreases, the potential of the connection point becomes higher, and when the resistance value of the second magnetoresistance effect element pattern 28b decreases, the potential of the connection point becomes lower.

[0042] Next, the mounting posture and mounting position of the first MR sensor 28 and the second MR sensor 30 with respect to the cylinder tube 16 will be described.

[0043] [Sensor installation posture]

[0044] The first MR sensor 28 is mounted on the outer side of the cylinder 16 in a posture that the C direction in which the first magnetoresistance effect element pattern 28a reacts is the A direction, and the D direction in which the second magnetoresistance effect element pattern 28b reacts is the B direction. Similarly, the second MR sensor 30 is also mounted on the outer side of the cylinder 16 in a posture that the direction in which the first magnetoresistance effect element pattern reacts is the A direction, and the direction in which the second magnetoresistance effect element pattern reacts is the B direction.

[0045] [Sensor installation position]

[0046] The first MR sensor 28 is installed at the following position: Figure 1 1 , the reference position shown in FIG. 1 is a position where the A direction component of the magnetic field 46 of the magnet 26 attached to the piston 18 is received the most. On the other hand, the second MR sensor 30 is installed at the right side of the first MR sensor 28 and at the position where the B direction component of the magnetic field 46 of the magnet 26 is received the most when the piston 18 is in the reference position. In other words, the first MR sensor 28 and the second MR sensor 30 are arranged with a predetermined distance L in the A direction so that when the first MR sensor 28 receives the A direction component of the magnetic field 46 of the magnet 26 the most, the second MR sensor 30 receives the B direction component of the magnetic field 46 of the magnet 26 the most.

[0047] In the present embodiment, the reference position of the piston 18 is defined as the time when the piston 18 positions and holds a workpiece (not shown) just before reaching the stroke end in the driving process of the piston 18 .

[0048] like Figure 4 As shown in FIG. 1 , when the piston 18 is located at a distance L to the right from the reference position, the first MR sensor 28 receives more of the B direction component of the magnetic field 46 of the magnet 26, and the second MR sensor 30 receives more of the A direction component of the magnetic field 46 of the magnet 26. Figure 5 As shown, when the piston 18 is located 2L to the right from the reference position, the first MR sensor 28 is hardly affected by the magnetic field 46 of the magnet 26 , and the second MR sensor 30 receives a large amount of the B-direction component of the magnetic field 46 of the magnet 26 .

[0049] Figure 6 1 is a graph showing the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 corresponding to the position X of the piston 18. The horizontal axis represents the position X of the piston 18, and the vertical axis represents the output of the sensor. The output V1 of the first MR sensor 28 is represented by a solid line, and the output V2 of the second MR sensor 30 is represented by a dotted line. The position X of the piston 18 takes the origin when the piston 18 is at the reference position, and takes a positive value when the piston 18 is located to the right of the origin. In addition, for convenience, the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 are shown including the case where the piston 18 passes the stroke end and is located to the left.

[0050] The output V1 of the first MR sensor 28 is the maximum value V when the piston 18 is at the origin (X=0). MAX , and is at its minimum value V when X=L MIN The output V2 of the second MR sensor 30 is at a maximum value V when X=L. MAX , and is at its minimum value V when X=0 and X=2L MIN The second MR sensor 30 is disposed at a predetermined distance L to the right of the first MR sensor 28 , so the waveform of the output V2 of the second MR sensor 30 is a waveform obtained by shifting the waveform of the output V1 of the first MR sensor 28 by the distance L in the positive direction of the horizontal axis.

[0051] The output of the first MR sensor 28 and the second MR sensor 30 when they are located far enough away from the magnet 26 and do not receive the magnetic field 46 of the magnet 26 at all is represented as a reference output Vs. The reference output Vs is compared with the maximum value V MAX The specified value between the two is set as the turn-on threshold V ON and the reference output Vs is equal to the minimum value V MIN The cut-off threshold V OFF .

[0052] like Figure 7 As shown, the sensor module 32 connected to the first MR sensor 28 and the second MR sensor 30 includes a control unit 34, a first comparison unit 36a to a fourth comparison unit 36d, a position determination unit 38, a first diagnosis unit 40, a second diagnosis unit 42, and a communication unit 44. ON and the cut-off threshold V OFF The data is stored in the control unit 34 .

[0053] The output V1 is input from the first MR sensor 28 to the first comparison section 36a, and the threshold value V ON The output V1 of the first MR sensor 28 is input to the first comparison unit 36a from the control unit 34. In the first comparison unit 36a, the output V1 of the first MR sensor 28 is compared with the on threshold value V ON When the output V1 of the first MR sensor 28 is the on threshold V ON When the comparison signal C1 is higher than the threshold value V1, the first comparison unit 36a increases the comparison signal C1, and the output V1 of the first MR sensor 28 is lower than the on threshold value V1. ON , the first comparing unit 36a causes the comparison signal C1 to fall.

[0054] The output V1 is input from the first MR sensor 28 to the second comparison unit 36b, and the cut-off threshold V OFF The output V1 of the first MR sensor 28 is compared with the cutoff threshold V OFF When the output V1 of the first MR sensor 28 is the cut-off threshold V OFF When the output V1 of the first MR sensor 28 is greater than the cutoff threshold V OFF , the second comparing unit 36b causes the comparison signal C2 to fall.

[0055] The output V2 is input from the second MR sensor 30 to the third comparison section 36c, and the threshold value V ON The output V2 of the second MR sensor 30 is input to the third comparison unit 36c from the control unit 34. In the third comparison unit 36c, the output V2 of the second MR sensor 30 is compared with the on threshold value V ON When the output V2 of the second MR sensor 30 is the on threshold V ON When the comparison signal C3 is higher than 0.01, the third comparison unit 36c increases the comparison signal C3, and the output V2 of the second MR sensor 30 is lower than the on threshold V ON , the third comparing unit 36c causes the comparison signal C3 to fall.

[0056] The output V2 is input from the second MR sensor 30 to the fourth comparison unit 36d, and the cut-off threshold V OFF The output V2 of the second MR sensor 30 is input to the fourth comparison unit 36d from the control unit 34. In the fourth comparison unit 36d, the output V2 of the second MR sensor 30 is compared with the cutoff threshold V OFF When the output V2 of the second MR sensor 30 is the cut-off threshold V OFF When the output V2 of the second MR sensor 30 is greater than the cutoff threshold V OFF, the fourth comparing unit 36d causes the comparison signal C4 to fall.

[0057] Figure 8 The states of comparison signals C1 to C4 corresponding to the position X of the piston 18 are shown. The comparison signal C1 is switched when the piston 18 reaches the position X3 which is slightly larger than X1. The comparison signal C2 is switched when the piston 18 reaches the position X2. The comparison signal C3 is switched when the piston 18 reaches the position X4 which is slightly smaller than X2. The comparison signal C4 is switched when the piston 18 reaches the position X1.

[0058] The comparison signals C1 to C4 are input to the position determination unit 38, and the position determination unit 38 determines whether the piston 18 has reached the specified position. The position determination unit 38 outputs the determination result as the switch signal SW to the control unit 34. The initial value of the switch signal SW is set to cut off. Figure 8 As shown, when both the comparison signal C1 and the comparison signal C4 are in a rising state, that is, when the piston 18 moves toward the origin and reaches the position X1, the position determination unit 38 switches the switch signal SW from off to on.

[0059] When both the comparison signal C2 and the comparison signal C3 are in a rising state, that is, when the piston 18 moves away from the origin and reaches the position X2, the position determination unit 38 switches the switch signal SW from on to off. Figure 8 The switching of the switch signal SW from off to on and from on to off are shown.

[0060] The control unit 34 can communicate with the outside in a two-way manner via the communication unit 44. The control unit 34 outputs a signal SW′, for example, indicating the lighting and extinguishing of a lamp (not shown) to the outside via the communication unit 44, based on the switch signal SW received from the position determination unit 38. In this case, the lamp is lit from the time when the piston 18 reaches the position X1 in the driving process of the piston 18 to the time when the piston 18 reaches the position X2 in the return process.

[0061] When the lamp is lit, it is known that the piston 18 has reached the end of the stroke of the driving process, and when the lamp is turned off, it is known that the return process of the piston 18 has just started. In addition, when the lamp is lit, it is known that the piston 18 is in a predetermined area near the rod cover 12. The switch signal SW can also be used to control an external device (not shown) that operates in association with the fluid pressure cylinder 10.

[0062] The sensor module 32 can be turned on from the outside. ON and the cut-off threshold V OFF When the control unit 34 receives the connection threshold V from the outside via the communication unit 44 ONand the cut-off threshold V OFF When the setting of the relevant data is changed, the control unit 34 outputs a new connection threshold value V to the first comparison unit 36a and the third comparison unit 36c. ON , and outputs a new cut-off threshold value V to the second comparison unit 36b and the fourth comparison unit 36d. OFF .

[0063] The magnetic force of the magnet 26 decreases (demagnetization) over time, and the sensitivity of the first MR sensor 28 and the second MR sensor 30 decreases when placed in a high temperature environment for a long time. When this happens, it also depends on the on threshold value V ON However, the maximum value V of the output V1 of the first MR sensor 28 is MAX or the maximum value V of the output V2 of the second MR sensor 30 MAX may be reduced to not exceed the turn-on threshold V ON degree.

[0064] Therefore, to monitor the maximum value V of the output V1 of the first MR sensor 28 MAX and the maximum value V of the output V2 of the second MR sensor 30 MAX The first diagnostic unit 40 and the second diagnostic unit 42 are provided for the purpose of determining whether the amount of the sensor decreases or exceeds the prescribed value due to time change, etc. The output V1 of the first MR sensor 28 is input to the first diagnostic unit 40, and the output V2 of the second MR sensor 30 is input to the second diagnostic unit 42. The processing contents in the first diagnostic unit 40 will be described below, but the processing contents in the second diagnostic unit 42 are the same.

[0065] The first diagnostic unit 40 includes a maximum value determination unit 40a, a maximum value storage unit 40b, and a monitoring unit 40c. Whenever the output V1 of the first MR sensor 28 changes from increasing to decreasing, the maximum value determination unit 40a uses the output at that time (for example, the output V1 just before it changes to decreasing) as the maximum value V1. MAX The maximum value storage unit 40b stores the maximum value V received from the maximum value determination unit 40a in a time series. MAX data.

[0066] The monitoring unit 40c periodically monitors the plurality of maximum values ​​V stored in the maximum value storage unit 40b. MAX The average value of the most recent specified number of data in the data is calculated and compared with the average value of the original specified number of data. Then, if it is determined that the average value of the most recent specified number of data is smaller than the average value of the original specified number of data by a specified value or more, a warning signal E1 is output to the control unit 34.

[0067] When receiving the warning signal E1 from the monitoring unit 40c of the first diagnosis unit 40, the control unit 34 notifies that the magnet 26 is likely to be demagnetized, the sensitivity of the first MR sensor 28 is reduced, and outputs the warning signal E1' to the outside via the communication unit 44. In this way, the operator can be urged to perform maintenance such as component replacement or to increase the threshold value V ON adjustments.

[0068] In the present embodiment, the maximum value V of the output V1 of the first MR sensor 28 is determined by the first diagnostic unit 40. MAX The second diagnostic unit 42 monitors the maximum value V of the output V2 of the second MR sensor 30. MAX However, the maximum value V of output V1 can also be monitored by the common diagnostic unit. MAX and the maximum value of output V2 V MAX Monitor the maximum value of output V1. MAX and the maximum value of output V2 V MAX When both of them decrease by more than a predetermined amount, the cause is likely to be demagnetization of the magnet 26, and when only one of them decreases by more than a predetermined amount, the cause is likely to be reduced sensitivity of the MR sensor. It is effective for a common diagnostic unit to distinguish these cases and output a warning signal.

[0069] Next, refer to Figure 9-10 , the case where the fluid pressure cylinder 10 is placed in an environment where various external magnetic fields are applied is described. Fig. 9 In the figures, the fluid pressure cylinder 10 is shown in a simplified manner.

[0070] (When there is a magnetic field from another cylinder)

[0071] like Fig. 9 As shown, it is assumed that the other fluid pressure cylinder 50 and the fluid pressure cylinder 10 are arranged side by side in the B direction, and the magnetic field 56 of the magnet 54 installed in the piston 52 of the other fluid pressure cylinder 50 acts on the first MR sensor 28 and the second MR sensor 30 of the fluid pressure cylinder 10. The magnetic field 56 acting on the first MR sensor 28 and the second MR sensor 30 changes according to the operating position of the other fluid pressure cylinder 50.

[0072] Fig.10An example of the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 based on the magnetic field 56 of the other fluid pressure cylinder 50 is shown. The horizontal axis represents the position of the piston 52 of the other fluid pressure cylinder 50 along the A direction, and the vertical axis represents the output of the sensor. The output V1 of the first MR sensor 28 is represented by a solid line, and the output V2 of the second MR sensor 30 is represented by a dotted line. The position of the piston 52 is taken as the origin at a position corresponding to the reference position of the piston 18 of the fluid pressure cylinder 10 in the A direction.

[0073] The distance in the B direction from the first MR sensor 28 and the second MR sensor 30 to the magnet 54 of the other fluid pressure cylinder 50 is greater than the distance in the B direction from the first MR sensor 28 and the second MR sensor 30 to the magnet 26 of the fluid pressure cylinder 10. Fig.10 As shown, the output V2 of the second MR sensor 30 is the cut-off threshold V OFF Therefore, the possibility of the switch signal SW being turned on and off is low, and when the magnetic field 56 of the other fluid pressure cylinder 50 acts, it is possible to prevent the erroneous detection that the piston 18 of the fluid pressure cylinder 10 is at the specified position. OFF By changing the setting so as to depart from the reference output Vs, it is possible to more reliably prevent erroneous detection.

[0074] (When welding magnetic field is applied)

[0075] Assume that the fluid pressure cylinder 10 is installed in the welding line, and the magnetic field (welding magnetic field) generated by the welding current acts on the first MR sensor 28 and the second MR sensor 30 of the fluid pressure cylinder 10. The welding magnetic field is different from the magnetic field of a magnet and is a magnetic field composed of a component in only one direction. The following description will be made by distinguishing between the case where the direction of the welding magnetic field is the A direction and the case where it is the B direction.

[0076] like Fig.11 As shown, it is assumed that a welding magnetic field 58 in the A direction acts on the first MR sensor 28 and the second MR sensor 30 . Fig.12 An example of the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 based on the welding magnetic field 58 is shown. The horizontal axis represents time, and the vertical axis represents the output of the sensor. Since the welding current is constant, when welding starts, the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 rise from the reference output Vs and then remain at a constant value Va. In addition, the output V2 of the second MR sensor 30 is consistent with the output V1 of the first MR sensor 28.

[0077] like Fig.12 As shown, although the above-mentioned certain value Va is the connection threshold V ONHowever, the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 will not become smaller than the reference output Vs, and the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 will not become the cutoff threshold Vs. OFF Therefore, the switch signal SW is not turned on and off, so when the welding magnetic field 58 in the A direction acts, it is possible to prevent the piston 18 from being erroneously detected to be at the predetermined position.

[0078] like Fig.13 As shown, it is assumed that a welding magnetic field 60 in the B direction acts on the first MR sensor 28 and the second MR sensor 30 . Fig.14 An example of the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 based on the welding magnetic field 60 is shown. The horizontal axis represents time, and the vertical axis represents the output of the sensor. Since the welding current is constant, when welding starts, the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 decrease from the reference output Vs and then remain at a constant value Vb. In addition, the output V2 of the second MR sensor 30 is consistent with the output V1 of the first MR sensor 28.

[0079] like Fig.14 As shown, although the above-mentioned certain value Vb is the cut-off threshold V OFF However, the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 will not become larger than the reference output Vs, and the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 will not reach the on-threshold value V ON Therefore, the switch signal SW is not turned on and off, and when the welding magnetic field 60 in the B direction acts, it is possible to prevent the piston 18 from being erroneously detected to be at the predetermined position.

[0080] (When a magnetic field such as a magnetized bolt is applied)

[0081] like Fig.15 As shown, it is assumed that a mounting member 62 such as a bolt used for assembling and mounting the fluid pressure cylinder 10 is magnetized by the welding magnetic field, so that a magnetic field 64 of the mounting member 62 acts on the first MR sensor 28 and the second MR sensor 30 of the fluid pressure cylinder 10 . Fig.16 An example of output V1 of the first MR sensor 28 and output V2 of the second MR sensor 30 based on the magnetic field 64 of the magnetized mounting component 62 is shown. The horizontal axis represents time and the vertical axis represents the output of the sensor. The output V1 of the first MR sensor 28 is represented by a solid line, and the output V2 of the second MR sensor 30 is represented by a dotted line.

[0082] A magnetic field (magnetic flux) 64 is formed around the magnetized mounting member 62, starting from one end side of the mounting member 62 and returning to the other end side of the mounting member 62, but the magnetic field 64 does not change at all. Therefore, at least the switch signal SW is not turned on or off, and when the magnetic field 64 of the mounting member 62 such as a magnetized bolt acts, it is possible to prevent the piston 18 from being erroneously detected to be at a predetermined position.

[0083] According to the fluid pressure cylinder 10 of this embodiment, two MR sensors 28 and 30 having a pair of magnetoresistive effect element patterns that respond to two directions orthogonal to each other are arranged at a predetermined interval L, thereby being able to detect the position of the piston 18 with good accuracy and preventing the position of the piston 18 from being erroneously detected even when various external magnetic fields act.

[0084] In addition, since the maximum value V of the output V1 of the first MR sensor 28 and the output V2 of the second MR sensor 30 is set MAX Since the first diagnostic unit 40 and the second diagnostic unit 42 that monitor the magnet 26 are reduced or more than a predetermined value, it is possible to easily know whether the magnet 26 is demagnetized or the sensitivity of the first MR sensor 28 or the second MR sensor 30 is reduced.

[0085] (Second Embodiment)

[0086] Next, refer to Figures 17 to 20 A fluid pressure cylinder 70 according to a second embodiment of the present invention will be described. In the fluid pressure cylinder 70 according to the second embodiment, components identical or equivalent to those of the above-described fluid pressure cylinder 10 are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.

[0087] The first embodiment is suitable for the case where the position of the piston 18 to be detected is near the rod cover 12, whereas the second embodiment is applicable even when the position of the piston 18 to be detected is not attached to the rod cover 12. That is, in the second embodiment, the reference position of the piston 18 can be set at an arbitrary position.

[0088] like Fig.17 As shown, on the outer side of the cylinder 16, the third MR sensor 72, which is a magnetic sensor using a magnetoresistive element, the first MR sensor 28, and the second MR sensor 30 are sequentially mounted in a row in the direction A. The interval between the third MR sensor 72 and the first MR sensor 28 is the same as the interval L between the first MR sensor 28 and the second MR sensor 30.

[0089] The third MR sensor 72 has the same structure as the first MR sensor 28, and is installed on the outer side of the cylinder 16 in a posture that the direction in which the first magnetoresistance effect element pattern responds is the direction A and the direction in which the second magnetoresistance effect element pattern responds is the direction B. Fig.17 At the reference position shown, the third MR sensor 72 receives the largest B-direction component of the magnetic field 46 of the magnet 26 , similarly to the second MR sensor 30 .

[0090] Fig.18 1 is a graph showing the output V1 of the first MR sensor 28, the output V2 of the second MR sensor 30, and the output V3 of the third MR sensor 72 corresponding to the position X of the piston 18. The horizontal axis represents the position X of the piston 18, and the vertical axis represents the output of the sensor. The output V1 of the first MR sensor 28 is represented by a solid line, the output V2 of the second MR sensor 30 is represented by a dotted line, and the output V3 of the third MR sensor 72 is represented by a two-dot chain line. The position X of the piston 18 takes the origin when the piston 18 is at the reference position, takes a positive value when the piston 18 is located to the right of the reference position, and takes a negative value when the piston 18 is located to the left of the reference position.

[0091] The output V1 of the first MR sensor 28 is the maximum value V when X=0. MAX , when X=L and X=-L, it is the minimum value V MIN The output V2 of the second MR sensor 30 is at a maximum value V when X=L. MAX , when X=0, it is the minimum value V MIN The output V3 of the third MR sensor 72 is the maximum value V when X=-L. MAX , when X=0, it is the minimum value V MIN The third MR sensor 72 is disposed at a predetermined distance L to the left of the first MR sensor 28 , so the waveform of the output V3 of the third MR sensor 72 is a waveform obtained by shifting the waveform of the output V1 of the first MR sensor 28 by the distance L in the negative direction of the horizontal axis.

[0092] like Fig.19 As shown, the sensor module 32 connected to the first MR sensor 28, the second MR sensor 30 and the third MR sensor 72 includes: a control unit 34, a first comparison unit 36a to a fifth comparison unit 36e, a position determination unit 38, a first diagnosis unit 40, a second diagnosis unit 42, a third diagnosis unit 43 and a communication unit 44.

[0093] The output V3 is input from the third MR sensor 72 to the fifth comparison unit 36e, and the threshold V ONThe output V3 of the third MR sensor 72 is compared with the on-threshold value V ON When the output V3 of the third MR sensor 72 is the on threshold V ON When the output V3 of the third MR sensor 72 is less than the on threshold V ON , the fifth comparing unit 36e causes the comparison signal C5 to fall.

[0094] Fig. 20 The states of comparison signals C1 to C5 corresponding to the position X of the piston 18 are shown. The comparison signal C1 is switched when the piston 18 reaches the position X3 which is slightly larger than X1 and when the piston 18 reaches the position -X3 which is slightly smaller than -X1. The comparison signal C2 is switched when the piston 18 reaches the position X2 and when the piston 18 reaches the position -X2. The comparison signal C3 is switched when the piston 18 reaches the position X4 which is slightly smaller than X2. The comparison signal C4 is switched when the piston 18 reaches the position X1 and when the piston 18 reaches the position -X1. The comparison signal C5 is switched when the piston 18 reaches the position -X4 which is slightly larger than -X2.

[0095] The comparison signals C1 to C5 are input to the position determination unit 38, and the position determination unit 38 determines whether the piston 18 has reached the specified position. The position determination unit 38 outputs the determination result as the switch signal SW to the control unit 34. The initial value of the switch signal SW is set to cut off. Fig. 20 As shown in FIG. 1 , when both the comparison signal C1 and the comparison signal C4 are in the rising state, the position determination unit 38 switches the switch signal SW from off to on. That is, when the piston 18 moves from the right direction to the origin and reaches the position X1 and when the piston 18 moves from the left direction to the origin and reaches the position -X1, the position determination unit 38 switches the switch signal SW from off to on.

[0096] In addition, when the comparison signal C2 and the comparison signal C3 are both in the rising state, that is, when the piston 18 moves away from the origin to the right and reaches the position X2, the position determination unit 38 switches the switch signal SW from on to off. Moreover, when the comparison signal C2 and the comparison signal C5 are both in the rising state, that is, when the piston 18 moves away from the origin to the left and reaches the position -X2, the position determination unit 38 switches the switch signal SW from on to off.

[0097] Fig. 20 1 shows the switching of the switch signal SW from off to on and from on to off. Fig. 20As can be understood, the switch signal SW is turned on when the piston 18 is present in a limited area centered at the origin, so it is possible to easily detect that the piston 18 is located near the reference position (origin).

[0098] The maximum value V of the output V3 of the third MR sensor 72 is MAX The third diagnostic unit 43 is provided for the purpose of monitoring whether the amount of energy has decreased by a predetermined amount or more due to time change, etc. The output V3 of the third MR sensor 72 is input to the third diagnostic unit 43. The processing content of the third diagnostic unit 43 is the same as that of the first diagnostic unit 40 described above.

[0099] According to the fluid pressure cylinder 70 of the present embodiment, the third MR sensor 72 is provided in addition to the first MR sensor 28 and the second MR sensor 30 . Therefore, the position of the piston 18 to be detected can be set at any position other than the vicinity of the rod cover 12 .

[0100] The fluid pressure cylinder of the present invention is not limited to the above-described embodiment, and various structures can be adopted without departing from the scope of the present invention.

Claims

1. A fluid pressure cylinder, wherein a first MR sensor (28) and a second MR sensor (30) mounted on a cylinder barrel (16) detect a magnetic field of a magnet (26) mounted on a piston (18), thereby detecting that the piston is located at a predetermined position, wherein the fluid pressure cylinder (10) is characterized in that: The first MR sensor and the second MR sensor are composed of a first magnetoresistance effect element pattern (28a) and a second magnetoresistance effect element pattern (28b), wherein the resistance value of the first magnetoresistance effect element pattern decreases in accordance with the strength of the magnetic field in a direction parallel to the axial direction of the piston, and the resistance value of the second magnetoresistance effect element pattern decreases in accordance with the strength of the magnetic field in a direction parallel to the radial direction of the piston, and the first MR sensor and the second MR sensor are arranged at a predetermined interval so that when the first MR sensor receives the most magnetic field component of the magnet in a direction parallel to the axial direction of the piston, the second MR sensor receives the most magnetic field component of the magnet in a direction parallel to the radial direction of the piston.

2. The fluid pressure cylinder according to claim 1, characterized in that: A sensor module (32) is provided, which is connected to the first MR sensor and the second MR sensor, and includes: a first comparing unit (36a) which compares the output of the first MR sensor with an on-threshold value greater than a reference output; a third comparing unit (36c) which compares the output of the second MR sensor with the on-threshold value; a second comparing unit (36b) which compares the output of the first MR sensor with a cut-off threshold value less than the reference output; and a fourth comparing unit (36d) which compares the output of the second MR sensor with the cut-off threshold value.

3. The fluid pressure cylinder according to claim 2, characterized in that: The sensor module includes a position determination unit (38), which switches a switch signal from off to on when the output of the first MR sensor is above the on threshold and the output of the second MR sensor is below the off threshold, and switches the switch signal from on to off when the output of the first MR sensor is below the off threshold and the output of the second MR sensor is above the on threshold.

4. The fluid pressure cylinder according to claim 2, characterized in that: The fluid pressure cylinder is capable of changing the settings of the on threshold value and the off threshold value.

5. The fluid pressure cylinder according to claim 1, characterized in that: A sensor module is provided, the sensor module being connected to the first MR sensor and the second MR sensor, the sensor module being provided with a diagnostic unit (40, 42) for monitoring whether the maximum value of the output of the first MR sensor and the maximum value of the output of the second MR sensor have decreased by more than a predetermined value.

6. A fluid pressure cylinder, wherein a first MR sensor, a second MR sensor and a third MR sensor (72) mounted on a cylinder barrel detect the magnetic field of a magnet mounted on a piston, thereby detecting that the piston is located at a predetermined position, wherein the fluid pressure cylinder (70) is characterized in that: The first MR sensor, the second MR sensor, and the third MR sensor are composed of a first magnetoresistance effect element pattern and a second magnetoresistance effect element pattern, the resistance value of the first magnetoresistance effect element pattern decreases corresponding to the strength of the magnetic field in a direction parallel to the axial direction of the piston, and the resistance value of the second magnetoresistance effect element pattern decreases corresponding to the strength of the magnetic field in a direction parallel to the radial direction of the piston. The first MR sensor, the second MR sensor, and the third MR sensor are arranged at a prescribed interval in a direction parallel to the axial direction of the piston so that when the first MR sensor receives the most magnetic field component of the magnet in a direction parallel to the axial direction of the piston, the second MR sensor and the third MR sensor receive the most magnetic field component of the magnet in a direction parallel to the radial direction of the piston.

7. The fluid pressure cylinder according to claim 6, characterized in that: A sensor module is provided, the sensor module is connected to the first MR sensor, the second MR sensor, and the third MR sensor, the sensor module comprises: a first comparing unit, the first comparing unit comparing the output of the first MR sensor with an on-threshold value greater than a reference output; a third comparing unit, the third comparing unit comparing the output of the second MR sensor with the on-threshold value; a second comparing unit, the second comparing unit comparing the output of the first MR sensor with a cut-off threshold value less than the reference output; and a fourth comparing unit, the fourth comparing unit comparing the output of the second MR sensor with the cut-off threshold value; and a fifth comparing section (36e) that compares the output of the third MR sensor with the turn-on threshold.

8. The fluid pressure cylinder according to claim 7, characterized in that: The sensor module includes a position determination unit, which switches the switch signal from off to on when the output of the first MR sensor is above the on-threshold and the output of the second MR sensor is below the off-threshold, and switches the switch signal from on to off when the output of the first MR sensor is below the off-threshold and the output of the second MR sensor is above the on-threshold and when the output of the first MR sensor is below the off-threshold and the output of the third MR sensor is above the on-threshold.

9. The fluid pressure cylinder according to claim 7, characterized in that: The fluid pressure cylinder is capable of changing the settings of the on threshold value and the off threshold value.

10. The fluid pressure cylinder according to claim 6, characterized in that: A sensor module is provided, which is connected to the first MR sensor, the second MR sensor and the third MR sensor. The sensor module has a diagnostic unit (40, 42, 43) that monitors whether the maximum value of the output of the first MR sensor, the maximum value of the output of the second MR sensor and the maximum value of the output of the third MR sensor are reduced by more than a specified amount.

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