JPH09229020A - Cylinder with position detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the cylinder excellent in pressure resistance and fixed in accuracy against the length. SOLUTION: A shaft center part of a piston rod 5 in a cylinder main body 1 is formed into a hollow part, a screw 10 is arranged in the shaft center part 9, a nut 13 engaged with this screw 10 is fixed to the piston rod 5, hence the rectilinear motion of the piston rod 5 is converted to the rotational motion of the screw 10, and a rotation sensor 15 arranged outside the cylinder main body 1 is connected to the screw 10. The position of the piston rod 5 can be detected by the rotation sensor 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder with a position detector for detecting a stroke position of a hydraulic cylinder, and more particularly to a high-precision position detector having excellent pressure resistance and constant accuracy with respect to length. It is related to the cylinder.

[0002]

2. Description of the Related Art Some hydraulic cylinders such as hydraulic cylinders are provided with a position sensor or a distance sensor outside or inside the cylinder body in order to detect the stroke position.
In the case where the sensor is arranged inside the cylinder body, for example, as shown in FIG. 3, the magnet 52 is assembled to the piston head 51 and the axial center portion 5 of the piston rod 53 is arranged.
4 is made hollow, and the cylinder main body 5
A rod 56 of a small diameter fixed to 5 is provided, a magnetostrictive wire is incorporated in the rod 56, and a signal generated in the magnetostrictive wire due to the movement of the magnet 52 is detected, and the moving distance of the piston rod 53 is detected from this signal. It has become.

[0003]

Since the conventional cylinder with a position detector has a structure in which the sensor is housed in the cylinder body, a high pressure due to hydraulic pressure is applied to the sensor. Depending on the pressure resistance of the sensor, reliability under such high pressure cannot be expected.

Further, since the position detection method is an analog method, it is inevitable that the detection accuracy becomes low for a long stroke.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a highly accurate cylinder with a position detector which is excellent in pressure resistance and whose accuracy is constant with respect to length.

[0006]

In order to achieve the above-mentioned object, the present invention forms a hollow shaft center portion of a piston rod in a cylinder body, arranges a screw in the shaft center portion, and meshes with the screw. A nut is fixed to the piston rod so that the linear movement of the piston rod is converted into the rotational movement of the screw, and a rotation sensor arranged outside the cylinder body is connected to the screw.

The axial center portion of the piston rod may be communicated with the head chamber.

[0008]

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

In the hydraulic cylinder with the position detector according to the present invention, in order to form the cylinder body 1, both ends of the cylindrical cylinder tube 2 are sealed with the rod flange 3 and the head flange 4, and the rod flange 3 A piston rod 5 is inserted through the piston rod 5 so as to be coaxial with the cylinder tube 2. Cylinder body 1 for piston rod 5
The outer tip is not shown. Cylinder body 1
A head 6 is formed on the outer periphery of the base end portion of the piston rod 5 inside, and the cylinder body 1 is partitioned by the head 6 into a head chamber 7 and a rod chamber 8. Head room 7
The working fluid can be supplied to and discharged from the rod chamber 8 and the rod chamber 8, respectively, so that the piston rod 5 can be stroked.

The axial center of the piston rod 5 in the cylinder body 1 is hollow. That is, the shaft center 9 is
It opens at the base end of the piston rod 5 and extends cylindrically in the direction of the tip of the piston rod 5 from this opening. The shaft center portion 9 has a depth substantially corresponding to the length of the cylinder tube 2.

A screw (ball spline) 10 is arranged in the shaft center portion 9. Screw 10
It is located at the center of the shaft center portion 9 and is rotatably and axially held by a bearing 11 in the head flange 4. One end of the screw 10 penetrates the outside of the head flange 4 to form a coupling portion 12. The opposite end of the screw 10 extends to the rod flange 3, and a thread is formed from this opposite end to the head flange 4. A nut 13 is provided so as to mesh with the thread of the screw 10, and the nut 13 is fixed to the piston rod 5 at the base end portion of the piston rod 5. That is, the nut 13 does not rotate with respect to the piston rod 5 and does not move in the axial direction.

Since the nut 13 is fixed to the piston rod 5 and the screw 10 is rotatably held by the bearing 11, the linear movement of the piston rod 5 is converted into the rotational movement of the screw 10. It will be. Of course, the piston rod 5 fixing the nut 13 is also configured not to rotate with respect to the cylinder body 1.

The screw pitch is set to such an extent that conversion from linear motion to rotary motion is not hindered. The screw 10 and the nut 13 used here are processed with high precision.

Seals 14 are attached to sliding parts and rotating parts in various places.
Is given.

A rotation sensor 15 is attached to the outside of the head flange 4, and the rotation shaft of the rotation sensor 15 is directly connected to the coupling portion 12 of the screw 10.

The rotation sensor 15 is classified into an analog type, a digital type, an incremental type that outputs a relative amount of rotation, an absolute type that outputs an absolute rotation angle, etc., depending on the output form. A rotary encoder including a slit disk and a light transmission sensor is used. The rotary encoder also has an incremental type and an absolute type. The output form and resolution can be appropriately selected depending on the purpose of use and the required measurement accuracy.

Next, the operation of the cylinder with the position detector will be described.

Since the linear movement of the piston rod 5 is converted into the rotational movement of the screw 10, the position of the piston rod 5 can be detected by looking at the rotation angle of the screw 10. Screw 1
Since 0 and the nut 13 are processed with high precision, there is no change in pitch, and the proportional relationship between the position and the rotation angle is constant over the entire stroke.

Rotation sensor 1 comprising a rotary encoder
5 can detect the rotation angle with high accuracy. Here, the screw pitch is set so that the rotation angle of one pulse that determines the resolution of the rotary encoder corresponds to a stroke of 10 μm. Therefore, the resolution of this cylinder with a position detector is 10 μm. In this way, if the screw 10 and the nut 13 are processed with high accuracy and the rotation sensor 15 with high accuracy is used, the piston rod 5
The position of can be detected with high accuracy.

The rotary encoder, which is a sensor, is arranged outside the cylinder body, and the components incorporated in the cylinder body for position detection are mechanical components such as the screw 10 and the nut 13. These mechanical parts have excellent pressure resistance, and even if high pressure due to hydraulic pressure is applied, they have no effect.

Next, another embodiment will be described.

The cylinder with a position detector shown in FIG. 2 has a structure in which the axial center of the piston rod is communicated with the head chamber in addition to the structure shown in FIG. That is, the other structure is the same as that of FIG. 1 and will not be described. However, in the structure of FIG. 2, the base end portion of the piston rod 5 opens toward the head chamber 7, and the nut passes through the inside of the head 6. A bypass 21 that communicates with the axial center portion that is deeper than 13 is provided.

Since the bypass 21 is provided, the shaft center portion 9 communicates with the head chamber 7 even if it is deeper than the nut 13. Therefore, the pressures applied to both sides of the nut 13 are equal, which makes the rotation of the screw 10 smooth and prevents the stroke of the piston rod 5 from being hindered by the pressure difference.

[0024]

The present invention exhibits the following excellent effects.

(1) Since there is no sensor in the cylinder body and only mechanical parts, the pressure resistance is excellent and the reliability is high.

(2) The detection accuracy is constant even if the stroke is long.

[Brief description of drawings]

FIG. 1 is a side sectional view of a hydraulic cylinder with a position detector showing an embodiment of the present invention.

FIG. 2 is a side sectional view of a hydraulic cylinder with a position detector showing another embodiment of the present invention.

FIG. 3 is a side sectional view of a conventional hydraulic cylinder with a position detector.

[Explanation of symbols]

 1 Cylinder Main Body 5 Piston Rod 9 Shaft Center 10 Screw 13 Nut 15 Rotation Sensor

Claims (2)

[Claims] 1. A piston rod in a cylinder body is formed with a hollow shaft center portion, and a screw is arranged in the shaft center portion,
A nut that meshes with the screw is fixed to the piston rod so that the linear motion of the piston rod is converted into the rotational motion of the screw, and a rotation sensor arranged outside the cylinder body is connected to the screw. Characteristic cylinder with position detector. 2. The cylinder with a position detector according to claim 1, wherein the axial center portion of the piston rod is communicated with the head chamber.