DEVICE FOR DETECTING POSITION OF A PISTON IN A FLUID PRESSURE CYLINDER

Abstract

 The invention refers to a device for detecting position of a piston in a fluid pressure cylinder by a magnetic sensor. The technical problem is how to conceive a device, in which the use of the material for the fluid pressure cylinder will not be limited to nonmagnetic materials, and to improve its reliability. The technical problem is solved by a device (1) for detecting a piston position in a fluid pressure cylinder, particularly in a hydraulic cylinder, comprising a fluid pressure cylinder (2), a piston (3) reciprocally slidable along the internal circumferential surface of the fluid pressure cylinder (2), a piston rod (4) connected with its first end with the piston (3) and projecting with its another end through the front side of the fluid pressure cylinder (2), a permanent magnet (5), the movement of which corresponds to the movement of the piston (3), and at least one magnetic switch (6) arranged on the external side of the fluid pressure cylinder (2) and susceptible to being actuated by said permanent magnet (5), wherein the permanent magnet (5) is arranged on the external side of the fluid pressure cylinder (2).

Description

Field of Invention

[0001] The invention refers to a device for detecting position of a piston in a fluid pressure cylinder by a magnetic sensor, particularly in a hydraulic cylinder.

Prior Art

[0002] Patent application US 4793241 A1 discloses a piston position detector for a fluid pressure cylinder operating by fluid pressure. The device comprises a non-magnetic cylinder, a piston sliding in the non-magnetic cylinder, an annular permanent magnet mounted circumferentially on the piston, and a magnetic detection element arranged on the outer surface of the cylinder to respond to the magnetic field formed by the permanent magnet, when the latter moves within the cylinder, and to generate electric signals. The cylinder is made of a non-magnetic material such as aluminium or non-magnetic steel.

Technical Problem

[0003] The technical problem is how to conceive a device for detecting a piston position in a fluid pressure cylinder, particularly a hydraulic cylinder, wherein the use of the material for the fluid pressure cylinder will not be limited to non-magnetic materials such as aluminium or austenitic steel, as a result, a less expensive material such as conventional structural magnetic steel can be used as the material for the fluid pressure cylinder. A further goal of the invention is to conceive a device featuring better operation reliability.

Solution to the Technical Problem

[0004] The technical problem is solved by a device for detecting a piston position in a fluid pressure cylinder, particularly in a hydraulic cylinder, comprising:

• a fluid pressure cylinder,
• a piston reciprocally slidable along the internal circumferential surface of the fluid pressure cylinder,
• a piston rod connected with its first end with the piston and projecting with its another end through the front side of the fluid pressure cylinder,
• a permanent magnet arranged on the external side of the fluid pressure cylinder such that its movement corresponds to the movement of the piston, and
• at least one magnetic switch arranged on the external side of the fluid pressure cylinder and susceptible to being actuated by said permanent magnet.

[0005] With both the permanent magnet and the magnetic switch being arranged outside the fluid pressure cylinder, the material selection is no longer limited to non-magnetic materials such as aluminium or austenitic steel. The fluid pressure cylinder can also be made of magnetic materials such as martensitic or ferritic steels. This broadens the spectre of possible materials and a less expensive material can thus be selected, such as conventional structural steel.

[0006] The device of the invention has many other advantages over the prior art. One of these advantages is better reliability and better precision in detecting magnetic flux lines of the permanent magnet. When a permanent magnet is arranged within a fluid pressure cylinder, the magnetic flux lines get distorted due to the influence of the wall of the fluid pressure cylinder, due to the accumulation of tiny metallic particles on the permanent magnet, and due to an increased temperature within the fluid pressure cylinder. During the operation, the fluid in the fluid pressure cylinder heats due to the increased pressure of the fluid. A permanent magnet exposed to an increased temperature has a weaker magnetic field, though. The device of the invention eliminates these drawbacks and the reliability of operation of the device is better, thus contributing to the extension of the life time of the device. A further advantage of the device of the invention is observed in the event of maintenance when a permanent magnet needs to be replaced; there is no need to interfere in the interior of the fluid pressure cylinder.

[0007] Figure 1: Device for detecting position of a piston in a fluid pressure cylinder

[0008] The invention is described in more detail hereinbelow.

[0009] The technical problem is solved by a device 1 for detecting a piston position in a fluid pressure cylinder, particularly in a hydraulic cylinder, comprising:

• a fluid pressure cylinder 2,
• a piston 3 reciprocally slidable along the internal circumferential surface of the fluid pressure cylinder,
• a piston rod 4 connected with its first end with the piston and projecting with its another end through the front side of the fluid pressure cylinder,
• a permanent magnet 5 arranged on the external side of the fluid pressure cylinder such that its movement corresponds to the movement of the piston 3, and
• at least one magnetic switch 6 arranged on the external side of the fluid pressure cylinder and susceptible to being actuated by said permanent magnet 5.

[0010] At the other end of the piston rod outside of the fluid pressure cylinder 2, a fixed arm 7 is foreseen, which carries a permanent magnet holder 8 arranged substantially parallel to the axis of the fluid pressure cylinder 2. The permanent magnet 5 is fastened on the permanent magnet holder 8. The permanent magnet holder 8 can be formed in the shape of a tube made of a non-magnetic material, in which the permanent magnet 5 is received.

[0011] The material of the fluid pressure cylinder 2 can also be selected among magnetic materials such as martensitic or ferritic steels.

[0012] The magnetic switch 6 is arranged on the external side of the fluid pressure cylinder either fixed or movable on a magnetic switch holder 9.

[0013] The magnetic switch 6 can be a Reed switch or any other switch formed by means of any known magnetic sensor, such as Hall, AMR, GMR, etc.

[0014] To better guide the permanent magnet holder 8, the fluid pressure cylinder 2 may be provided with a guide 10 formed as a through hole in a flange 11 of the fluid pressure cylinder, said through hole being formed in its axial direction.

[0015] When the device operates, the piston moves within the fluid pressure cylinder. The movement of the piston is transferred from the piston rod 4, the arm 7 and the permanent magnet holder 8 to the permanent magnet 5. When the permanent magnet 5 reaches the area of the magnetic switch 6, the latter detects the magnetic field of the permanent magnet and generates a signal for the control of the piston 3.

Claims

1. A device (1) for detecting a piston position in a fluid pressure cylinder, particularly in a hydraulic cylinder, comprising:

- a fluid pressure cylinder (2),

- a piston (3) reciprocally slidable along the internal circumferential surface of the fluid pressure cylinder (2),

- a piston rod (4) connected with its first end with the piston (3) and projecting with its another end through the front side of the fluid pressure cylinder (2),

- a permanent magnet (5), the movement of which corresponds to the movement of the piston (3), and

- at least one magnetic switch (6) arranged on the external side of the fluid pressure cylinder (2) and susceptible to being actuated by said permanent magnet (5),

characterized in that
the permanent magnet (5) is arranged on the external side of the fluid pressure cylinder (2).

2. Device (1) or claim 1, characterized in that at the other end of the piston rod outside of the fluid pressure cylinder (2), a fixed arm (7) is foreseen, which carries a permanent magnet holder (8) arranged substantially parallel to the axis of the fluid pressure cylinder (2).

3. Device (1) of claim 2, characterized in that the permanent magnet (5) is fastened on the permanent magnet holder (8).

4. Device (1) of claim 2 or 3, characterized in that the permanent magnet (5) is fastened on the permanent magnet holder (8).

5. Device (1) of any of claims 2 to 4, characterized in that the permanent magnet holder (8) is formed in the shape of a tube made of a non-magnetic material, in which the permanent magnet (5) is received.

6. Device (1) of any of preceding claims, characterized in that the material of the fluid pressure cylinder (2) is selected among martensitic or ferritic steels.

7. Device (1) of any of preceding claims, characterized by comprising a magnetic switch holder (9), on which the magnetic switch (6) is arranged in a movable manner.

8. Device (1) of any of preceding claims, characterized in that the magnetic switch (6) is a Reed switch.

9. Device (1) of any of claims 1 to 7, characterized in that the magnetic switch (6) is formed with a magnetic sensor, selected among a Hall sensor, AMR or GMR.

10. Device (1) of any of claims 2 to 9, characterized in that the fluid pressure cylinder (2) is provided with a guide (10) formed as a through hole in a flange (11) of the fluid pressure cylinder, said through hole being formed in its axial direction.

Drawing