DE4244078A1 - Method and measuring system for detecting the position of a body - Google Patents

Abstract

In a measuring device for detecting the travel position of a first body with respect to a second body of a device, for example a shock absorber, having two bodies (piston 10 and cylinder 4) movable relative to each other along a travel path, a continuously variable position signal, corresponding to the travel position of the piston (10) is produced along the travel path, and a marking signal is produced by additional means (82) for at least one defined travel position thereof. The fine, continuous position signal is thus corrected at precise position(s) and measuring errors are minimised. The device described uses coil(s) on the piston (10) and a conductive tube (60) around the cylinder and provided with a V-slot (68). The marking signals at precise positions are produced by slots (82) in a further tube (80). Coil (40) is supplied with a.c. at two frequencies. <IMAGE>

Description

State of the art

The invention is based on a method according to the Preamble of claim 1.

Such a method is known for example from the DE-OS 40 29 633 known. In the known method or the known measuring system for performing this The process is integrated according to the sensor principle Travel sensor worked, the inductance a measuring coil using a magnetizable mate rials or an electrically highly conductive material in Dependent on the position either directly magnetically or indirectly according to the eddy current principle is so influenced that along the travel a continuously variable sensor output signal results.

In the known system, the sensor element is over a wiring harness with the evaluation electronics in the sensor chassis control unit connected. Because the sensor elements in this configuration not matched who  who can, with regard to the temperature response, the Zero offset and the sensitivity larger tolerances occur.

The object of the invention is based on the known method or measuring system a new Ver drive or indicate the measuring system, with the tolerances influencing the accuracy of the measurement results Parameters can be reduced to a minimum.

Advantages of the invention

In the inventive method for detecting the Position of a first body against a two th body and in the measuring system according to the invention to carry out this procedure, the Object according to the invention by the features of the kenn drawing part of claim 1 and the patent Claim 2 solved, with the important advantage shows that on the one hand the high sensitivity of the well-known continuous path measurement fully used that can, and on the other hand with the help of marker signals for at least one defined position a parameter influencing the measurement result during of ongoing operations can be corrected.

The basic principle of procedures and measuring system according to The invention is to be seen in the fact that one very sensitive continuous fine measurement with time and temperature-dependent parameters, so to speak, a rough measurement for one or a few positioning positions superimposed is going to this way when going through one or fewer travel positions Additional information the instantaneous values of one or more parameters  to get and then these parameters accordingly correct to reduce the measurement error to a minimum adorn, and not just at the specified position position or the specified positioning positions, but continuously for the entire measuring path, which is equal to the Be travel or one or more measurement technology may include areas of interest thereof.

In principle, a marking signal for one or more Positioning positions using mechanical or non-contact working switching devices are obtained, the Elements at defined locations relative to each other movable body attached, being special is advantageous, the location of the at least one position position so that it is in a measurement process in in practice in any case after a very short time is run through; for example, as a position the neutral position of the relatively movable Body selected for a given purpose become.

In an embodiment of the invention, however, it is special advantageous if the additional devices an the induc activity and / or the resistance of a measuring coil in at least one defined position of the first Body material influencing such that when passing this position by the first Body from the measuring coil a pulse-shaped marking signal is produced. The material can advantageously a magnetically active, especially highly permeable Be material that the inductance and / or the Active resistance of the measuring coil directly influenced, or also an electrically good conductive material, by Spei solution of the measuring coil with an alternating current eddy currents can be generated, the frequency-dependent the Indukti  vity and / or the effective resistance of the measuring coil indirectly influence.

A measuring system has proven to be particularly advantageous proven in which the inductance and / or the Active resistance of the measuring coil influencing material is electrically good conductive material and in which the Measuring coil for generating eddies flow in this mate rial with an alternating voltage or alternating current predetermined frequency is fed. With this Ausge staltung, the generation of a along the travel continuously variable measurement signal enables the additional devices are then preferably configured in this way det that they are an AC power source for feeding the Measuring coil with a second AC voltage or a include second alternating current, the frequency of which is clear is lower than the predetermined frequency for the first AC voltage. This will make a larger, radial one Depth of penetration of the eddy currents into the electrical well conductive material is reached, when in this Material at least one discontinuity is provided, which corresponds to a predetermined position at Passing the discontinuity through the measuring coil due to of the alternating current flowing through them lower Fre a pulse-shaped marking signal can be generated.

Further advantageous refinements and improvements of the inventive method and the Invention according measuring system according to claims 1 and 2 are the subject of further dependent claims.

drawing

Further details and advantages of the invention will be explained in more detail below with reference to a drawing.  

Show it:

Figure 1 is an axial longitudinal section through a tube shock absorber with a displacement measuring system according to the invention.

Figure 2 is a schematic diagram for explaining the course of a continuously variable position signal to the actuator travel.

Fig. 3 is a schematic representation of the course of an additional signal with individual marking signals over the travel range; and

Fig. 4 is a schematic representation for explaining tion of a constructive variant for the generation of marking signals.

In particular, FIG. 1 shows a single-tube shock absorber 2, wherein a non-interest here, central section of this shock absorber 2 is omitted, to be able to represent the other parts in a larger scale. The shock absorber 2 essentially comprises a cylinder 4 with a jacket 5 , a first end face 6 and with a second end face 8 , and a damper piston 10 and a piston rod 12th The damper piston 10 is mounted axially displaceably within the cylinder 4 along an inner surface 14 of the jacket 5 . The piston rod 12 is connected at one end to the damper piston 10 and projects at its other end through the first end face 6 beyond the cylinder 4 . An opening provided at the first end side 6 of gasket 15 seals a leakage gap between the end face 6 and the piston rod 12th The protruding in the axial direction Rich over the cylinder 4 end of the piston rod 12 is connected to a first mass 16 . The second end face 8 of the cylinder 4 is articulated to a second mass 18 . The first mass 16 is, for example, a vehicle body and the second mass 18 is, for. B. a vehicle axle. An interior of the cylinder 4 is divided by the damper piston 10 into a first working space 21 and a second working space 22 . The first working space 21 is located on the first end face 6 of the damper piston 10 and the second working space 22 is located on the second end face 8 of the damper piston 10 . In the drawing, the first working space 21 is above and the second working space 22 is below the damper piston 10 . To compensate for volume differences when retracting and extending the piston rod 12 z. B. the second working space 22 with a memory 24 be the. The two working spaces 21 , 22 and the memory 24 are at least partially filled with a pressure medium.

The two working spaces 21 , 22 are connected to one another via at least one flow connection 26 . In the flow connection 26 , for example, an electrically controllable solenoid valve 28 can be provided. Throttling of the pressure medium when flowing through the flow connection 26 can be influenced via the solenoid valve 28 . The solenoid valve 28 is connected via a line 32 to an electronics 30 provided in the first mass 16 and can be controlled via the electronics 30 . In addition to the flow connection 26 , further flow connections 34 can be provided for connecting the two working spaces 21 , 22 . Within half of the other flow connections 34 z. B. check valves 35 may be provided. The Strömver connection 26 and the further flow connections 34 are arranged within the damper piston 10 in the illustrated embodiment.

An annular groove 38 is provided on an outer jacket 36 of the damper piston 10 . A measuring coil 40 is located within the annular groove 38 . The measuring coil 40 comprises at least one coil 42 and preferably also a core 44 . The core 44 consists, for. B. made of a soft magnetic, highly permeable material and largely surrounds the coil 42 , but leaves the coil 42 on an outer periphery facing the jacket 5 free. The coil 42 preferably consists of an insulated, multi-layer wound and electrically conductive wire. The coil 42 is just if connected to the electronics 30 via a line 32 . The core 44 significantly improves the effect of the measuring coil 40 .

In addition to the measuring coil 40 or instead of the measuring coil 40 , another measuring coil 46 or a measuring coil 48 can also be provided. The other measuring coil 46 is located on the damping piston 10 on the first working space 21 facing th end face and the other measuring coil 48 is arranged on the second working space 22 facing the front side of the damper piston 10 . The measuring coils 46 , 48 also comprise a coil 42 and a core 44 . In principle, a coil 42 and thus one of the measuring coils 40 , 46 , 48 is sufficient for the position measuring system according to the invention and, depending on the circumstances, only one of the measuring coils 40 or 46 or 48 will be arranged as cheaply as possible. Explanations for the measuring coil 40 also apply to the other measuring coils 46 , 48 .

The jacket 5 of the cylinder 4 has an outer jacket surface 54 . A material 60 which influences an inductance of the coil 42 is arranged on the outer lateral surface 54 of the cylinder 4 .

The material 60 influencing the inductance can, for example, as shown in DE-OS 40 29 633, Fig. 2, have an axially V-shaped recess 68 to enable the generation of a continuously variable position signal as shown in FIG. 2. Other possibilities for the design of the material or the material layer 60 to achieve this goal are described in the cited publication.

The measuring coil 40 is in the axial direction, ie in Rich direction of the parallel to the longitudinal axis of the shock absorber 2 ver adjustment path significantly shorter than the maximum allowable travel. On the other hand, the material influencing the inductance extends at least over the entire length of the measuring path, the material 60 surrounding the measuring coil in the exemplary embodiment in the region of the first end face 6 over a larger circumferential angle than in the region of the second end face 8 . Depending on the position of the measuring coil 40 or the coil 42 relative to the cylinder 4 , the influence of the material 60 is consequently more or less large. Furthermore, the influence of the material 60 on the inductance and, if applicable, the effective resistance of the measuring coil 40 or the coil 42 is a measure of the position of the measuring coil 40 along the travel path or with respect to the cylinder 4 .

In the exemplary embodiment, the material influencing the inductance and / or the effective resistance, with its special structure or geometric configuration explained above, is an electrically good conductor of the most non-magnetic material, such as, for. B. copper or aluminum. On the other hand, the jacket 5 at least along the travel path preferably made of an electrically poorly conductive and non-magnetic material, for example from a suitable, high-alloy steel. In this case, the inductance of the measuring coil 40 or the coil 42 is relatively large if it is located in the region of the second end face 8 , since in the region of the relatively wide recess 68 no eddy currents are generated which have an effect on their back the measuring coil could reduce its inductance and / or its effective resistance. In contrast, in the area of the first end face 6 , the inductance of the measuring coil 40 or the coil 42 is relatively small, since at this point eddy currents are generated in the material 60 practically over the entire circumference of the measuring coil. Since the width of the recess 68 changes constantly along the actuating path, there is thus the possibility of detecting any actuating position on the basis of the inductance of the measuring coil determined. A continuously variable position signal according to FIG. 2 is thus obtained along the actuating path, depending on the supply of the measuring coil 40 or the coil 42 with an alternating current with a predetermined frequency f1.

The structured material 60 is surrounded by a shield tube 80 according to FIG. 1, in which recesses 82 are provided at predetermined intervals along the actuating path. If the measuring coil 40 is additionally fed with an alternating voltage, the frequency f2 of which is significantly lower than the frequency f1, so that there is a greater penetration depth in the radial direction outwards for the magnetic alternating field generated by the coil 40 , then changes the inductance of the measuring coil for this second frequency f2 jumps suddenly when one of the cutouts 82 of the shielding tube 80 , which is made of a good electrical conductor, is passed while driving through the adjustment path. So there are abrupt changes in the coil inductance and / or the effective resistance thereof, which are superimposed on the continuous change in these parameters of the coil as a function of the material 60 . In addition to the continuous "fine signal" f according to FIG. 2, a "coarse signal" g is obtained as shown in FIG. 3. This signal can be processed with the help of the electronics 30 so that along the travel path for defined positioning positions, the position of which corresponds to the position of the recesses 82 of the shield tube 80 , result in marking signals or pulses M as shown in the lower part of FIG . 3 is shown. Corresponding results are obtained if recesses 82 are provided in the structured material 60 even at suitable locations, as is shown in the schematic sketch in FIG. 4. In particular, if the markings or recesses are provided directly in the magnetically active material, the shield tube can possibly be omitted.

From the above description it is clear that in the method according to the invention there is the possibility of simultaneously generating a fine signal according to FIG. 2 and a coarse signal according to FIG. 3 when passing through the adjustment path, the coarse signal being used to scale the fine signal, which is changes continuously along the travel path. In particular, when detecting a single marking signal M according to the invention, it is already possible to recognize and correct a zero point shift of the fine signal. As soon as a further marking signal M is then detected in the course of a measurement process, there is the possibility of additionally adjusting the sensitivity of the sensor system with regard to the fine signal and, to a certain extent, of correcting the slope of the device schematically representing the fine signal in FIG . As a result, depending on the detection of two marking signals, the sensitivity and the zero point shift for the fine signal can be detected and corrected according to the respective requirements, which is preferably done with the aid of a microprocessor which calculates the required correction values from the measured values associated storage devices are stored and necessary if updated, so that - possibly apart from a short start phase - corrected measured values are available which are very precise and consequently enable the generation of very precise control signals, for example for the solenoid valve 28 .

The signal voltage waveforms f and g shown in FIGS . 2 and 3 over the travel range are only to be understood qualitatively, the evaluation circuit, as mentioned preferably a microprocessor, in a manner known to the person skilled in the art and therefore not to be explained in more detail here is designed and programmed in such a way that the processes aimed for signal acquisition and evaluation are achieved.

Finally, it should be pointed out that under a continuously variable position signal or a continuous measurement signal to understand a signal which is continuous along the entire measuring path or the sections of the same is generated, whereby also a digital signal in the sense of the present application is considered a continuous signal, although a Signal change, unlike an analog signal, can only be done in predetermined, small steps.

Claims (11)

1. A method for detecting the position of a first body relative to a second body of a device having two bodies movable relative to one another along an adjustment path, in particular a shock absorber, in which a position signal continuously variable along the adjustment path is generated by means of a measuring device according to the position of the first body is characterized in that a marker signal is generated by means of additional devices for at least one defined position of the first body. 2. Measuring system for detecting the position of a first body versus a second body one Device with two relative to each other along one Travel movable bodies, especially one Shock absorber, with a measuring device through which one according to the position of the first body pers continuously variable along the travel range Position signal can be generated to carry out the Method according to claim 1, characterized in that additional devices before are seen through which for at least one defi position of the first body is a marker signal can be generated.   3. Measuring system according to claim 2 with a measuring device device comprising a measuring coil on the first body and the inductance of the second body Measuring coil influencing material, which along the Travel one with the position analog ver has a knotted structure, characterized in that the additional devices a the inductance and / or the effective resistance of the Measuring coil in at least one defined position tion of the first body rial include that when passing this Stellposi tion through the first body from the measuring coil pulse-shaped marking signal can be generated. 4. position measuring system according to claim 2 with a measuring device tion with two coils, one of which is as with excitation fed by an electrical alternating voltage trained coil and ver with one body is bound and the other of which is a measuring coil trained and connected to the other body is such that, depending on the the distance between the two coils variable electroma the variable posi tion signal can be generated, characterized in that the additional devices a the inductance and / or the effective resistance of the Measuring coil in at least one defined position tion of the first body rial include that when passing this Stellposi tion through the first body from the measuring coil pulse-shaped marking signal can be generated.   5. position measuring system according to one of claims 2 to 4, characterized in that the additional devices are designed such that along the travel for at least two defined positions of the first body each generate a marker signal is. 6. Position measuring system according to claim 3, in which the induct activity and / or the resistance of the measuring probe influencing material an electrically good conductive Material is and in which the measuring coil for generation of eddy currents in the electrically highly conductive Material with an alternating current given Fre quenz is fed, characterized in that the additional devices an AC power source for feeding the measuring coil include a second alternating current whose frequency is significantly lower than the specified frequency for the first alternating current to a larger, radia depth of penetration into the electrically well conductive To achieve material and that in the electrically good conductive material at least one of a given corresponding discontinuity is seen such that when passing the discount continuity through the first body from the measuring coil due to the alternating current applied to it higher frequency a pulse-shaped marking signal can be generated. 7. position measuring system according to one of claims 1 to 6, characterized in that evaluation devices are provided, with the help of the Messein direction generated position signal depending from the appearance of a marker signal to increase the Measuring accuracy is changeable.   8. position measuring system according to claim 7, characterized net that the evaluation devices trained in such a way det are that through them a zero point shift of the position signal depending on a mar Kiersignal is correctable. 9. position measuring system according to claim 8, characterized net that the evaluation devices trained in such a way det are that depending on minde at least one more, another defined Marking signal assigned to the position at least another parameter of the position signal with the Aim to improve the accuracy of measurement is cash. 10. position measuring system according to claim 9, characterized net that the evaluation devices trained in such a way det are that through it depending on two Marking signals the two defined positions are assigned, the zero point shift of the Position signal and the sensitivity of the measurement direction can be corrected. 11. measuring system according to one of claims 7 to 9, characterized in that arithmetic and storage directions are provided with the help of Dependency on at least one marking signal min a correction value for the position signal or can be calculated and saved for the measuring device can be saved.