DE10222618A1 - Arrangement for determining axial shaft position has electrically or magnetically conductive coaxial ring or plate at least partly between coils, evaluation device for coaxial sensor unit signals - Google Patents

Abstract

The arrangement has at least one electrically or magnetically conductive ring or plate (2) coaxially in or on the shaft (1), two sensor units coaxial to the shaft, each with at least one cylinder coil (3,4) and axially offset with respect to each other in relation to the shaft, whereby the ring or plate is a arranged at least partly between the coils, and an evaluation device for the sensor unit signals.

Description

The invention relates to an arrangement for determination the axial position of a shaft.

According to the prior art (DE 42 13 507 A1) a device for contactless measurement of the axial Wave of a rotating body described. she consists from a wheel rigidly connected to the rotating body Made of soft magnetic material, the edge of which is designed in this way is that it rotates periodically as the body rotates axial direction relative to a magnetic field sensor and egg magnet in the immediate vicinity moved back and forth. The magnetic field sensor switches on everyone Passing the edge, and there is a pulse train,  whose duty cycle is linear and independent of the temp rature is related to the axial position.

This device belongs to the prior art the disadvantage that he has a minimum rotation speed is required that the manufacture of the wheel with the ge shaped edge is complex and that a very accurate posi tionation of the magnetic field sensor compared to the wheel must be led. In addition, the pretense is egg ner significant axial movement by tilting the Axis possible in the shaft in the bearing.

This last-mentioned disadvantage is also apparent in the The arrangements described in EP 0 716 241 A1 for determining tion of the axial position of a magnetic shaft canceled. Here are two sensors in axial Direction are spaced apart used. This is but only advantageous in that the extension of the Wave with an increase in temperature when regulating the Po sition of the shaft in the bearing can be taken into account. This works the better the further both sensors go others are removed. But at the same time grows with the Ent Removal of both sensors resulting from a tilt errors.

It also belongs to the state of the art (DE 42 15 381 A1) an arrangement for radial position ser version of a shaft with two sensor units, each at least from a pair of diametrically opposite Sensors exist. From the output signals of the sensors a pair, a difference signal is determined, which in the The center position of the shaft has the value "zero". To increase the There are two pairs of sensors for each measuring direction  seen from their difference signals with a summer a mean value is formed with switchable inputs.

Has this arrangement belonging to the prior art the disadvantage that it is due to the large number of sensors is cumbersome and expensive.

The technical problem underlying the invention consists of a sensor arrangement for determining the axi to indicate the position of a shaft which is a simple, ro bust and inexpensive mechanical structure and has good linearity.

This technical problem is addressed by arrangements the features of claim 1 or claim 2 ge solves.

According to the invention are two sensor units, which each consist of at least one solenoid, pre see. The sensor units, i.e. the solenoids are coaxial to the shaft and axially with respect to the shaft staggered, that is, the solenoids are spaced apart. On or in the Wave is at least a ring or a plate and / or we at least one groove arranged, the ring, the plate or the groove in turn at least partially between the Cylinder coils are arranged or projecting into them is trained. There is also an evaluation unit device for evaluating the signals of the sensor units in the form of the solenoid coils.

The ring, the plate or the groove is from the shaft deflected in the axial direction.  

The coils are advantageously short, with a large inside diameter and with an outer diameter that is only small is larger than the inner diameter.

Both coils are of one in amount and phase flow through the same sine current. Alternatively, one Bridge arrangement of the two coils and two ohmic Wi with a sine voltage. The difference the voltage drops are evaluated as a useful signal.

The ring, the plate or the groove forms electrically a short circuit winding. If the ring, the plate or the groove in the middle is both inductance ten equal (zero differential voltage). With axial approach the inductance of a coil becomes smaller due to the Mutual inductance, which becomes the inductance of the other coil accordingly larger. The effect is related to a coil nonlinear, results from the difference evaluation however, a linear useful signal.

The invention describes a simple structure and cost-effective differential displacement sensor for axial magnet la with good linearity over a large travel range. He is used to measure the axial position of a shaft. The Sensor is suitable both for attachment to a free one Shaft end as well as for installation in any axial Position along the shaft.

The arrangement according to the invention is characterized records that by changing the electrical and / or magnetic properties of the shaft in the axial direction an opposite change in inductance of the two coils when the shaft is deflected along the common coil axis  is achieved so that a linea res sensor signal can be obtained.

An example of an arrangement according to the invention is given below:
With a plate diameter of eleven millimeters, a plate thickness of three millimeters, an inner coil diameter of fourteen millimeters and an average axial coil spacing of seven millimeters, this typically results in a linear travel range of four millimeters. When supplying a bridge circuit, which is formed from the two coils and two ohmic resistors, with a 20 kHz sinusoidal voltage with an effective value of five volts, a signal swing of 100 millivolts per millimeter can be expected as the differential voltage.
When the ring, plate or slot passes through the center of the coil, the phase of the differential voltage is reversed. Due to the difference evaluation, the useful signal is largely insensitive to interference such as temperature.

If the ring, the plate or the groove in the Located in the middle, the material temperature of the plate has kei influence.

The influence of the Material temperature very low. Therefore it is recommended to use only half of the sensor characteristic. Avoid detects the phase reversal and the associated risk of Non-linearities in the evaluation of the signal.  

The inventive design of the differential path sensors with two active coils has the advantage that one simple, robust and inexpensive mechanical construction is present. The very good linearity is also advantageous over a very large path area. Another advantage of large linear path range are the very low requirements changes in mechanical tolerances. It is not a match required. Another advantage is the double sensation compared to sensors with only one active coil watching.

The arrangement according to the invention also has the advantage that with a suitable design of the coil body, the sensor Vacuum sealing for turbomolecular pumps can.

In addition, only passive electro are advantageous African components used, and it is therefore an operation in radioactive environment possible.

Alternatively, the measurement signal can be evaluated directly the. Alternatively, it can also be transmitted via a cable the.

The arrangement according to the invention is advantageously rotati constructed asymmetrically, so that a rotation of the shaft does not affect the sensor signal. Material Inhomogenitä the circumference, which is often a big problem with radial magnetic bearings ß problem, affect the sensor signal Not. The sensitivity of the sensor to radial The shaft is slightly offset.

The coils can be in a plastic bobbin be ordered. The bobbin can be open on one side  Have hole in which the shaft engages. However, it is also possible to provide two holes so that the shaft can take hold.

The shaft extension that is in the bobbin grips, can be made of plastic. It can be advantageous Ring can then be made of aluminum. However, there are other material combinations are also possible.

A particular advantage of the arrangement according to the invention is that positioning is much easier is like the positioning of individual point sensors, as it belongs to the prior art (DE 42 15 381 A1). The sensor units used according to the invention, which as Cylinder coils are formed only in the axial Direction can be adjusted while that to the state of the art belonging point sensors both an axial and make radial adjustment unavoidable.

Is the ther in the working temperature range on the shaft mixed expansion of importance, so in the regulation the position of the axis point of the shaft, which is exactly in the The middle between the two sensor units is constant held.

The edges of the ring, plate or groove can on the one hand between the two solenoids in axial Seen in the direction of the shaft. However, it is also possible that the edges of the ring, the plate or the groove in the cylinder which is encompassed by each coil space are arranged.

The edges of the ring, plate or groove can also outside of the spaces covered by the coils and outside  ßer the space between the coils in the axial Seen in the direction of the shaft.

As already stated, the shaft end can, for example be made of plastic and the ring made of aluminum minium. A shaft can be manufactured particularly cost-effectively Extension made of aluminum with a rectangular cross Enlarged section (plate).

A transition between two different is important Chen electrically conductive materials, for example wise a metal / air transition, a metal / metal transition, where the metals have different electrical conductivity features or a transition between a metal and a non-electrically conductive material. Also through a transition between two different magnetic conductive materials is an opposing inductor change in the sensor units.

The ring, the plate or the groove with the associated sensor units can be placed at any point on the Shaft arranged. The post will be after the possible Space chosen. It is possible the ring, the plate or to arrange the groove at the end of the shaft.

The arrangement according to the invention advantageously serves Control of the axial position of a shaft with a magnetic bearing. It can be used for a shaft with a magnetic bearing, the part of a compressor, part of a liquid pump or is part of a turbomolecular pump.

Further details of the invention can be found in the Unteran sayings are taken.  

In the drawing is an embodiment of the He shown, namely:

Figure 1 shows a first embodiment of an arrangement according to the invention with a ring on the end of a shaft in longitudinal section.

Fig. 2 shows a modified embodiment;

Fig. 3 shows a modified embodiment with a plate at the end of the shaft;

Fig. 4 shows a modified embodiment;

Figure 5 shows a shaft with a groove in longitudinal section.

Fig. 6 is a shaft having a recessed ring in longitudinal section;

Figure 7 shows an arrangement of coils in a coil body made of plastic, in longitudinal section.

Cut 8 is an arrangement shown in FIG 7 with a sätzlichen to aluminum housing in longitudinal..;

Fig. 9 shows a basic circuit of the sensor and the evaluation electronics.

Fig. 1 shows a shaft ( 1 ) with an electrically lei tend ring ( 2 ) which is arranged between two coaxial with the shaft ( 1 ) arranged solenoids ( 3 , 4 ). The Zy cylinder coils ( 3 , 4 ) are axially offset at a short distance. The ring ( 2 ) is arranged on one end ( 5 ) of the shaft ( 1 ).

According to Fig. 2 of the ring (2) is arranged (5) spaced position of the shaft (1) in an end to the waves.

Referring to FIG. 3, the plate (2), which is arranged at the shaft end (5) of the shaft (1), formed from the same electrically conductive material as the shaft (1).

Fig. 4 shows a plate ( 2 ), the edges ( 6 ) of the solenoids ( 3 , 4 ) enclosed spaces ( 7 ) are net angeord. Alternatively, the edges ( 6 ) can be arranged between the cylinder coils ( 3 , 4 ), as is shown in dashed lines in FIG. 4.

Referring to FIG. 5, the shaft (1) has a groove (8). The edges ( 9 ) of the groove ( 8 ) are arranged outside the spaces ( 7 ) encompassed by the coils and also outside the space between the coils ( 3 , 4 ).

Fig. 6 shows a shaft ( 1 ), in which the ring ( 2 ) is left. The ring ( 2 ) has a different electrical or magnetic conductivity from the shaft ( 1 ).

The ring of FIG. 6 can also be the entire cross section (not shown) of the shaft (1) filled in.

Fig. 7 shows the coils ( 3 , 4 ), which are arranged in a coil body ( 10 ). The coil former ( 10 ) has an open bore ( 11 ) through which the shaft ( 1 ) which carries the ring ( 2 ) is inserted. This coil former ( 10 ) can, for example, take over the vacuum seal in turbomolecular pumps.

According to Fig. 8, the coil body (10) with the Senso ren (3, 4) disposed in an aluminum housing (12) for minimizing the interference by an electrically conductive environment or an electromagnetically disturbed environment countries to verhin. All parts are rotationally symmetrical.

Fig. 9 shows a basic circuit of the sensor and the evaluation electronics. Both are optionally located in the immediate vicinity or connected for operation, for example in a radioactive environment, using a cable that is, for example, three meters long.

The current supplied by the sine generator (80 kHz, 3 V _RMS ) is distributed symmetrically over the coils via two 300 Ω resistors. The resistors are arranged on the sensor side so that asymmetries in the cable have as little influence as possible. The 560 Ω resistors at the output are necessary in order to compensate for the signal increase caused by the cable capacitance wire / screen.

The differential voltage is transmitted via a twisted pair to eliminate common mode interference. The inner screens ( 13 , 14 ) lying on one side on ground reduce crosstalk. An outer shield ( 15 , 16 ) placed on both sides of the housing ( 17 , 18 ) ensures electromagnetic compatibility.

In the evaluation circuit, a differential amplifier ( 19 ), each with 10 kΩ input resistance, forms the raw signal for the actual position value. Despite the high gain, there are no high demands on its offset properties, since only the AC voltage component is processed further. This is converted into a proportional proportional voltage to the position using conventional methods (precision rectifier or synchronous rectifier with subsequent low-pass filter of higher order).

reference numerals

1

wave

2

Ring or plate

3

solenoid

4

solenoid

5

shaft end

6

Edge of the ring or plate

7

of solenoids (

3

.

4

) enclosed space

8th

groove

9

Edges of the groove

10

bobbins

11

drilling

12

casing

13

inner shield

14

inner shield

15

external shield

16

external shield

17

Housing of the evaluation circuit

18

Housing of the sensor

19

differential amplifier

Claims (15)

1. Arrangement for determining the axial position of a shaft, characterized in that at least one ring ( 2 ) or a plate ( 2 ) made of an electrically or magnetically conductive material is arranged coaxially on or in the shaft ( 1 ) that two ko axially to the shaft ( 1 ) arranged sensor units, which are each formed from at least one solenoid ( 3 , 4 ), are provided, which are axially offset with respect to the shaft ( 1 ), and that the at least one ring ( 2 ) or Plate ( 2 ), seen in the axial direction of the shaft ( 1 ), is at least partially arranged between the solenoids ( 3 , 4 ), and that an evaluation device for evaluating the signals from the sensor units ( 3 , 4 ) is provided. 2. Arrangement for determining the axial position of a shaft, characterized in that the shaft ( 1 ) has at least one groove ( 8 ) that two coaxial to the shaft to ordered sensor units, each of which is formed from at least one solenoid ( 3 , 4 ) are provided, which are arranged axially with respect to the shaft ( 1 ) to each other, and that a groove base of the at least one groove ( 8 ), seen in the axial direction of the shaft ( 8 ), at least partially between the solenoids ( 3 , 4 ) is arranged, and that an evaluation device for evaluating the signals of the sensor units ( 3 , 4 ) is provided. 3. Arrangement according to claim 1 or 2, characterized in that the edges ( 6 , 9 ) of the at least one Rin ges ( 9 ) or plate or the at least one groove ( 8 ) derspulen in an axial direction of the shaft between the Zylin ( 3 , 4 ) lying space are arranged. 4. Arrangement according to claim 1 or 2, characterized in that the edges ( 6 , 9 ) of the ring ( 2 ), the plate ( 2 ) or the groove ( 8 ) in each of one of a cylinder coil ( 3 , 4 ) included space ( 7 ) are arranged. 5. Arrangement according to claim 1 or 2, characterized in that the edges ( 7 , 9 ) of the ring ( 2 ), the Tel lers ( 2 ) or the groove ( 8 ) outside the gap between the coils ( 3 , 4th ) and outside the spaces ( 7 ) enclosed by the coils ( 3 , 4 ). 6. Arrangement according to claim 1 or 2, characterized in that the solenoid coils ( 3 , 4 ) are designed as coils with several turns. 7. Arrangement according to claim 1 or 2, characterized in that the edges ( 6 , 9 ) of the ring ( 2 ) or the groove ( 8 ) through a metal / air transition, a metal / Me tall transition or a metal / Non-metal transition are formed. 8. Arrangement according to claim 1 or 2, characterized in that the ring ( 2 ), the plate ( 2 ) or the groove ( 8 ) at one end ( 5 ) of the shaft ( 1 ) is arranged. 9. Arrangement according to claim 1 or 2, characterized in that the position of the in the shaft ( 1 ) arranged ring ( 2 ) with a different from the electrical conductivity of the shaft ( 1 ) electrical conductivity is measurable. 10. Arrangement according to claim 1 or 2, characterized in that the position of the in the shaft ( 1 ) arranged ring ( 2 ) is measurable with a different from the permeability of the shaft ( 1 ) permeability. 11. Arrangement according to one of the preceding claims, characterized in that the arrangement is part of a mag netlagers is. 12. The arrangement according to claim 11, characterized net that the arrangement part of the magnetic bearing of a ver is more poetic. 13. Arrangement according to claim 11, characterized net that the arrangement part of the magnetic bearing of a river liquid pump is. 14. Arrangement according to claim 11, characterized in net that the arrangement part of the magnetic bearing of a turbo molecular pump is. 15. Arrangement according to one of the preceding claims, characterized in that two identical sensors are provided hen are, the signals of both sensors by the Rege the same value.