DE102006047966A1 - Piston position sensor e.g. magnetostrictive sensor, for e.g. hydraulic cylinder, has sliding unit made of abrasion-resistant material e.g. polyamide, with high slidability in comparison with wave guide unit of sensor unit - Google Patents

Abstract

The sensor e.g. magnetostrictive sensor (2), has a rod-shaped sensor unit, and a sliding unit (1) is provided with a position transducer e.g. position magnet such as ring magnet (3). The sliding unit is made of an abrasion-resistant material e.g. polyamide (PA) and polyether ether ketone (PEEK), with high slidability in comparison with a wave guide unit of the sensor unit. The sliding unit has a frictional co-efficient in comparison to the sensor unit.

Description

I. Field of application

The The invention relates to position or velocity sensors.

II. Technical background

Positions and speed sensors are often based on external influence Magnetic fields, z. B. after the magneto-inductive or magneto-strictive Operating principle.

at such sensors, the current position of the monitored Component determined by a mounted on this component position sensor in terms of its position to the rest of the sensor, namely the sensor unit, detected becomes.

ever according to the principle of operation, the position sensor is for example a Metal part or a magnet that is both one-sided next to the sensor unit can be arranged and moved or this also as a ring Enclose the socket can. The following is to simplify the naming of the parts merely by way of example and not limiting the invention of a magnetostrictive sensor, where the sensor unit is referred to as waveguide unit and the position sensor as magnet or ring magnet.

One typical application for this is a hydraulic cylinder or pneumatic cylinder to the position to determine the piston in the cylinder.

The Waveguide unit is firmly attached in the head of the cylinder and protrudes into a central bore in the interior of the piston. The position-giving ring magnet is in the front, expanded End of this central bore mounted in the piston rod.

Even though the inner diameter of the ring magnet is chosen larger than the outer diameter The waveguide unit, however, both still not rarely rub against each other in their relative movement, since the waveguide unit only one-sided is fixed and due to lengths up to about 6 meters laterally can be significantly deflected, was it by vibrations and shocks during the Operation or even due to its own weight in non-vertical, but weird or horizontal installation.

kick on the side of the ring magnet caused by friction wear, the to destruction the magnet and thus the inoperability of the entire sensor to lead can and requires an exchange of the magnet, so are the Follow - up costs due to downtimes of the corresponding system in usually higher as the cost of the sensor itself.

Often comes It also leads to a tilting of the magnet with the waveguide unit and to a resulting kinking and destruction of the waveguide unit, which is also due to previously occurred excessive wear on the inner circumference of the Magnet or too small axial guide length is conditional.

Also the bushes made of aluminum previously used to hold the magnets or brass have solved these problems only partially by their Friction coefficient was not optimal and also their guide length.

In addition exists the possibility, that both the wear behavior and the abrasion occurring as well as the tilting of the position sensor, in particular ring magnet and buckling of the waveguide unit through within the cylinder locally developing pressure conditions favored is caused by the fact that the magnet as a throttle point for the hydraulic medium acts.

there Functionally not necessarily hydraulic fluid into the central hole for the waveguide unit in the piston rod beyond the ring magnet but the ring magnet never reliably seals this space, because in this case it is the high working pressure present in the piston would have to resist.

on the other hand is the radial clearance too low, than that the ring magnet is not as a throttle for the Fluid flow into this space would be considered.

III. Presentation of the invention

a) Technical task

It is therefore the object according to the invention, a sliding member for receiving the position sensor of a z. B. magnetostrictive To create sensors or a sensor equipped with it, the easy and cost-effective is to manufacture and avoids the disadvantages of the prior art.

b) solution the task

These Task is solved by claim 1. Advantageous embodiments emerge from the dependent claims.

Also for the following description of the invention is exemplified by the position sensor as a magnet and by the Sensorein unit as a waveguide unit, and thus based on a magnetostrictive sensor, without limiting the invention thereto, which is applicable to all sensors mentioned above.

By doing the sliding member in which the magnet is arranged, one sufficient good lubricity over the Waveguide unit and a high abrasion resistance comes it to no destruction by wear by means Abrasion.

By doing the radial clearance between the inner circumference of the bush and the outer circumference the waveguide unit is kept very low at the same time greater axial length of support between the two, there can be no tilting when moving come of the magnet. Preferably, therefore, the sliding element is made a material with high sliding coefficients, in particular a Plastic like PA or PEEK manufactured, which in addition also a small one Coefficient of friction the waveguide unit, which is mostly made of steel or titanium, has, a good cold flow behavior and a low water absorption.

Of the Magnet is close to the inner diameter of the slider arranged so that only a thin radial inner wall separates it from the inner diameter of the bush, so that it is at an optimal distance from the waveguide unit.

The axial extent of the sliding element should at least the double the diameter, better four times the diameter of the sensor element correspond. By contrast, the radial clearance between the two should be maximum +/- 0.5 mm, but not less than +/- 0.1 mm of the shaft unit, to avoid tilting.

To this avoidance carries also the chamfering or strong rounding of the ends of the inner peripheral surface at.

Around the carrying length as big as possible To design, the inner diameter of the sliding element relative to the outer diameter axially even extended, so that the sliding element fixing snap ring in a recess in the outer circumference the sliding element is arranged.

The axial flow channels through the sliding element through, be it designed as holes or Grooves in the outer circumference, enable a pressure equalization between both sides and thus avoidance local pressure buildups. The ends serve the same purpose Flow grooves, the the mouths these flow channels with the inner diameter and connect the local blind hole of the receiving piston rod.

While at a one-piece design of the sliding element of the magnet almost forcibly close is received at one of the axial ends of the sliding element can in a two-part training in the form of two together subsequent Divide the magnet in an annular groove of one of the faces that the contact surface represents the other sub-element, be housed and thus about in the middle length range of the sliding element and in addition well protected against any kind of damage.

To This purpose is the magnet - the two sides or flanked on one side by Flussleitstücken, which is also usually annular can be - in the corresponding annular Grooved glued or potted, or even by means of a corresponding Projection of the other sub-element positively held.

The Both sub-elements are radially relative to each other centered by means of an annular flange on the outer circumference of the one partial element, which engages in a corresponding recess of the other part element.

In the rear face the sliding element is further an elastomeric element, for. B. an O-ring, half let in arranged in an annular groove which serves as a buffer ring at the stop of the sliding element on the floor of him receiving Blind-hole recess.

The Both sub-elements are preferably glued, alternatively also bolted, and the entire sliding element is preferably by means of a snap ring held in the recess provided.

c) embodiments

embodiments according to the invention in the following example closer described. Show it:

1 : the application case in a hydraulic piston and

2 : another type of sliding element.

1a shows a longitudinal section of a built-in hydraulic piston-cylinder unit according to the invention magnetostrictive sensor 2 with its tubular waveguide unit 2a and the axially adjacent, widened head housing 2 B ,

Here is the sensor 2 with his head housing 2 B from the outside up on the piston crown that sets the tubular waveguide unit 2a through the cylinder bottom 21a in the longitudinal direction centrally in the interior of the cylinder 21 extends and into the cylinder 21 retracting piston rod 20 in a central blind hole 22 this piston rod 21 is recorded.

The ring magnet 3 is in the widened mouth of this blind hole 22 fixed and thus moves with the piston rod 20 with whose position is to be monitored.

This makes it immediately clear that when a necessary change of the ring magnet 3 the piston / cylinder unit must be dismantled and for this purpose beforehand drained the hydraulic medium and then refilled and vented, causing costs and lost time.

In the enlarged partial view of the 1b the sliding element is easier to recognize:
A moving out of the magnet from the blind hole is by a snap ring 5 prevented, which engages positively in an annular groove of the piston rod.

An O-ring, half sunk in an annular groove, serves as a buffer ring 4 axially between the sliding element 1 and the bottom of the recess and thus the piston rod 20 ,

The inner diameter 7 of the sliding element 1 , which consists of abrasion-resistant, lubricious and especially self-lubricating, temperature-resistant and chemically resistant to the hydraulic medium plastic is formed axially longer than the outer diameter 11 to the guide length relative to the waveguide unit 2a to be as big as possible.

Axial flow channels 12 penetrate the guide bush 1 from one to the other end face and are positioned so that both the buffer ring 4 as well as the snap ring 5 at least not completely cover their mouths, preferably not at all.

In addition, in the end face of the sliding element 1 that of the piston rod 20 facing, radially across the mouth of each flow channel 12 running flow grooves 6 present, to the inner diameter 7 go through and thus blind hole 22 to lead.

The ring magnet 3 is in a frontally open recess 13 housed by the inside diameter 7 is separated from a narrow inner wall and to the buffer ring 4 indicative end face of the sliding element 1 is formed out.

Within the flow channels 12 go the flow grooves 6 radially over the recess 13 away, so the ring magnet 3 not axially into the area of the flow grooves 6 extends.

The axial ends of the inner diameter 7 are as introductory radius 8th educated.

2 shows a second design of the sliding element 1' as a separate component.

In contrast to 1 is the sliding element 1 it consists of two sub-elements 1a , B, which adjoin one another in the axial direction and wherein a partial element 1a on the outer circumference of an annular flange 14 and the other at the appropriate location an annular recess 15 containing the two sub-elements 1a , b radially centered.

The flow channels 12 extend in alignment through the two sub-elements, wherein the alignment can be most easily achieved by some of the flow channels 12 be used for pinning or screwing the sub-elements against each other.

The annular recess 13 in the ring magnet 3 sits, is located in the socket 1b , so that the ring magnet is approximately in the middle of the axial extent of the inner diameter 7 the socket 1 located.

The inner wall between the recess 13 and the inside diameter 7 is dimensioned as thin as possible to the ring magnet 3 as close as possible to the inside diameter 7 and thus the waveguide unit 2a in bringing.

In this case, the ring magnet 3 axially adjacent to two likewise annular Flussleitstücken 16 flanked, and this entire magnet arrangement in the recess 13 by means of an adhesive or a potting compound 9 fixed.

Another difference is in the solution of 2 the buffer ring 4 radially within the mouths of the flow channels 12 arranged.

However, the circulation by means of hydraulic fluid is made possible by the local mouths of the flow channels 12 by means of one of the radially extending flow grooves 6 in the face with the inner diameter 7 connected deeper than the groove for the buffer ring 4 are formed, preferably also to the outside to the outer diameter 11 go through.

1

Slide

1a, b

partial elements

2

magnetostrictive sensor

2a

Waveguide unit

2 B

head case

3

position magnet

4

buffer ring

5

snap ring

6

flow groove

7

Inner diameter

8th

insertion radius

9

potting compound

10

bonding

11

outer diameter

12

flow channel

13

recess

14

annular flange

15

recess

16

flux conductor

20

piston rod

21

cylinder

21a

cylinder base

22

Blind hole

Claims (24)

Position sensor, in particular magnetostrictive or magnetoinductive sensor ( 2 ) with a rod-shaped sensor unit and a position sensor, in particular a position magnet ( 3 ), in particular a ring magnet, characterized in that - the position sensor in a sliding element ( 1 ) made of abrasion-resistant material, in particular plastic with high lubricity with respect to the sensor unit, in particular with respect to the waveguide unit ( 2a ), consists. Sliding element ( 1 ) for a position sensor, characterized in that the sliding element ( 1 ) made of abrasion-resistant plastic with high lubricity with respect to the waveguide unit ( 2a ) consists. Position sensor or sliding element ( 1 ) according to claim 1 or 2, characterized in that the plastic has a sliding wear of less than 10 microns / km, and in particular polyamide (PA) or polyetheretherketones (PEEK) is. Sliding element ( 1 ) according to one of the preceding claims, characterized in that the sliding element relative to the sensor unit has a coefficient of friction of less than μ = 1.0. Sliding element ( 1 ) according to one of the preceding claims, characterized in that the sliding element has a time-expansion stress of less than 1.5 N / μmm ² . Sliding element ( 1 ) according to one of the preceding claims, characterized in that the material of the sliding element has a swelling of less than 8% by hydraulic oil. Sliding element ( 1 ) according to one of the preceding claims, characterized in that the plastic has a water absorption of less than 3%. Sliding element ( 1 ) according to one of the preceding claims, characterized in that the plastic is chemically resistant to conventional hydraulic fluid oils. Sliding element ( 1 ) according to one of the preceding claims, characterized in that the at least one position sensor close to the inner diameter ( 7 ) of the sliding element ( 1 ) is arranged, in particular by a radial inner wall of the inner diameter ( 7 ) separated. Sliding element ( 1 ) according to one of the preceding claims, characterized in that the axial extension of the sliding on the sensor unit inner diameter ( 7 ) of the sliding element ( 1 ) is at least 0.5 times the diameter of the sensor unit. Sliding element ( 1 ) according to one of the preceding claims, characterized in that the axial extension of the sliding on the sensor unit inner diameter ( 7 ) of the sliding element ( 1 ) is at least twice the diameter, better four times the diameter of the sensor element. Sliding element ( 1 ) according to one of the preceding claims, characterized in that the clearance between inner diameter ( 7 ) of the sliding element and outer diameter of the sensor unit is not more than +/- 0.5 mm, but not less than +/- 0.1 mm at the minimum. Sliding element according to one of the preceding claims, characterized characterized in that the ends of the sliding inner peripheral surface bevelled or are strongly rounded. Sliding element according to one of the preceding claims, characterized in that the axial extent of the sliding element on the outer circumference ( 11 ) is less than the inner diameter ( 7 ). Sliding element according to one of the preceding claims, characterized in that the sliding element axial flow channels ( 12 ) in the form of through holes or grooves in the outer circumference ( 11 ) having. Sliding element according to one of the preceding claims, characterized in that the frontal mouths of the flow channels ( 12 ) on at least one end face with radial flow grooves ( 6 ) in the end face, in particular the inner diameter ( 7 ) to the outer diameter ( 11 ) of the sliding element. Sliding element according to one of the preceding claims, characterized in that the sliding element is formed in two parts with two adjoining each other in the axial direction, in particular slightly overlapping in the axial direction part sockets ( 1a , b). Sliding element according to one of the preceding claims, characterized in that the sub-elements ( 1a , b) are relatively centered by a circumferential radial positive annular flange ( 14 ) on one of the subelements ( 1a ) and a corresponding recess ( 15 ) on the other subelement ( 1b ). Sliding element according to one of the preceding claims, characterized in that in one of the end faces of the sliding element to the inner diameter of an annular groove for partially receiving an O-ring as an axial buffer ( 4 ) is available. Sliding element according to one of the preceding claims, characterized in that the position sensor is a magnet ( 3 ), in particular a ring magnet, and in particular axially on each side of an annular flux guide ( 16 ) is adjacent. Sliding element according to one of the preceding claims, characterized in that the position sensor, in particular the ring magnet ( 3 ) or the entire magnet arrangement in an annular, in particular only frontally open, recess ( 13 ) used and fixed, z. B. glued, in particular potted. Sliding element according to one of the preceding claims, characterized in that the recess ( 13 ) in the contact end face of the one subelement ( 16 ) is trained. Sliding element according to one of the preceding claims, characterized in that the two partial elements ( 1a , b) are screwed or glued against each other. Sliding element according to one of the preceding claims, characterized in that the outer diameter ( 11 ) of the sliding element is inserted with radial clearance in an unbending component and in particular by means of a snap ring ( 5 ) is held in a blind hole.