FR2647893A1 - RACE MEASURING DEVICE FOR DETECTING THE RELATIVE POSITION OF A BODY IN RELATION TO ANOTHER - Google Patents

Abstract

Stroke measuring device of a set of two bodies slidable to detect the position of one of the bodies relative to the other body, in which a part of the stroke measuring device surrounding several coils is linked to one of both bodies. It is characterized in that the other part respectively linked to the other body of the stroke measuring device surrounds a short-circuited coil 60 and in that a part of the stroke measuring device comprises a supply coil 50 and a measuring coil 52, 54.

Description

Stroke measuring device for detecting the

  relative position of one body relative to another ".

  The invention relates to a stroke measuring device for detecting the relative position of a body with respect to another body in which a part of the stroke measuring device surrounds

  several coils and is linked to one of the two bodies.

  A stroke measuring device is already known in which a part of the measuring measuring device is connected to one of the bodies and another part of the measuring device is connected to the other body, and by means of which the measuring device can be measured. position of the first body relative to the other body and wherein a part of the stroke measuring device surrounding

  several coils are linked to one of the two bodies.

  The known stroke measuring device operates according to the well-known transformer principle. A supply voltage is applied to a first coil. The measurement voltage induced in a second coil can be measured and displayed or otherwise exploited. Each coil is connected to a body. A soft magnetic core linked to the other body moves between these two coils. According to the respective position of the two bodies, the electromagnetic coupling of the two coils is different and thus also the measurement voltage in the second coil. The measuring voltage in the second coil is a measure for the position of a body relative to

to the other.

  In the known stroke measuring device, it is necessary that the soft magnetic core of a body

  passes relatively close to the coils of the other body.

  For a larger distance, the coupling of the two coils is insufficient and it is not possible to obtain in the second measuring voltage coil validly

exploitable.

  The invention is characterized in that the other part respectively connected to the other body of the stroke measuring device surrounds a coil in

short circuit.

  The device of the invention is characterized in that a body corresponds to a feed-line and at least one measuring coil. Sure

  the other body, there is a coil in short circuit.

  This arrangement allows an impeccable measurement even

  for a large distance between the two bodies.

  If a room has been equipped with

  stroke measurement of only two coils, that is,

  say of a feed reel and a reel of

  measure, we obtain a low-rise construction.

  If one of the parts of the stroke measuring device is equipped with a supply coil and two measuring coils, a particularly easy measurement signal is obtained.

treat.

  One embodiment of the invention is shown in simplified form and its operation is explained in more detail in the

following description.

  The stroke measuring device according to the invention can be used in devices where it is necessary to determine the position of a body relative to another body. Depending on the position of one body relative to the other body, a certain measurement signal is obtained. At each position corresponds a determined measurement signal. By the processing of this signal, it is possible to detect for example what displacement

  had a body in relation to the other body.

  Without limiting the scope of the invention, the embodiment of the present patent application is an example of application to a damper. The embodiment shown in the drawing represents what is called a bitubular damper. The bitubular damper essentially comprises an inner cylinder 2, an outer cylinder 4, a damper piston 6, a piston rod 8 and a protective cap 10. The inner cylinder 2 has a first end face 12 and a second end face 14 The outer cylinder 4 also has a first end face 16 and a second end face 18. The first end face 12 of the inner cylinder is connected to the first end face 16 of the outer cylinder 4 by a piece of tube 19. Above the first end face 16 of the outer cylinder 4 exceeds the piston rod 8. The piston rod 8 passes through the first two end faces 12, 16 of the two cylinders 2, 4 and passes into the inner cylinder 2. The piston rod is integral with the damping piston 6 with its end located in the inner cylinder 2. The piston rod 8 is connected to a first mass 20 by the other end coming out of the outer cylinder 4. The second front face the 18 of the outer cylinder 4 is connected to a second mass 22. The first mass 20 is for example a vehicle frame and the second mass 22 is for example a vehicle axle. The damper piston 6 can slide axially on the inner liner 24 of the inner cylinder 2. An inner chamber of the inner cylinder 2 is shared by the damper piston 6 into a first chamber of

  Work 26 and a second working chamber 28.

  In the drawing, the first working chamber 26 is above and the second working chamber 28 is below the damper piston 6, so that between the outer cylinder 4 and the inner cylinder 2, a balancing chamber 30. The two working chambers 26, 28 and the balancing chamber 30 are filled at least partially

a pressure agent.

  The two working chambers 26, 28 are connected by a first valve 32 formed in the damper piston 6 and a second valve 34 also formed in the damper piston. In the second end face 14 of the inner cylinder 2 are formed a third valve 36 and a

fourth valve 38.

  By penetration of the piston rod 8 into the inner cylinder 2 the pressure medium flows out of the second pressure chamber 28, through the first valve 32 into the first working chamber 26. Thus, one moves into the second working chamber 28 more pressure agent than he can

  to flow into the first working chamber 26.

  Therefore, by penetration of the piston rod 8, a portion of the pressure medium passes from the second working chamber 28 through the fourth valve 38 into the balancing chamber 30. During the penetration of the rod piston 8 in the inner cylinder 2, the second valve 34 and the third valve 36 are closed. The pressure medium can flow from the second working chamber 28 into the first working chamber 26 through the first valve 32 without significant braking. Braking of the pressure medium determining the damping of the damper, takes place during the penetration of the piston rod 8 into the inner cylinder 2 by braking the agent of

  pressure at the passage of the fourth valve 38.

  When the piston rod 8 leaves the inner cylinder 2, the pressure medium exits the first working chamber 26 through the second valve 34 into the second working chamber 28. In the second working chamber 28, however, more pressure medium may flow than is discharged from the first press-on chamber 26. This is why pressure agent flows from the equilibration chamber 30 through the third valve 36 in the second working chamber 28. The pressure agart flows through the third valve 36 largely without braking. A damping at the exit of the piston rod 8 is caused by the braking of the pressure medium as it passes through the second valve 34. When the piston rod 8 is released from the inner cylinder 2, the first valve 32

  and the fourth valve 38 are closed.

  A seal 42 placed in the tube piece 19 between the two first end faces 12, 16 of the inner cylinder 2 and the outer cylinder 4 prevents leakage of the first working chamber 26 outward along the guide set 44. between the piston rod 8 and the tube piece 19. A hole 46 connects to the balancing chamber 30 a portion of the guide clearance between the seal 42 and the first working chamber 26. The hole 46 serves to protect the seal 42 of a too high pressure consecutive to the current caused by the rise of the piston rod 8. The protective cap 10 is connected to

  the end of the piston 8 connected to the first mass 20.

  The protective cap 10 surrounds at least

  partially the outer cylinder 4.

  On a cylindrical portion 48 of the protective cap 10, a supply coil, a first measuring coil 52 and a second measuring coil 54 are placed. The cylindrical portion 48 of the protective cap 10 preferably consists of plastic material. The supply spool 50 and the two measuring coils 52, 54 are molded into the cylindrical portion 48 of the protective cap 10. On the outer wall face 56 of the

  outer cylinder 4, a coil

  circuit 60. The short-circuited coil 60 is protected from environmental influences at least in part

  by a housing 62 made of plastic.

  As the cylinder portion 48 of the protective cap 10 is connected only on one side to the piston rod 8 and as a result of the negative influences of the environment, to which the damper is partly subjected, it is necessary that there is between the cylindrical piece 48 and the short-circuited coil 60 with

  the housing 62 a game 64 relatively important.

  The supply spool 50 has been placed on the cylindrical portion 48 of the protective cap 10 so that the supply spool 50 surrounds the short-circuited coil 60 for each position of the piston rod 8. The coil 50 is located between the two measuring coils 52, 54. The first measuring coil 52 approaches one side, axially of the supply coil 50, and on the axially opposite side of the supply coil 50 is the second measuring coil. The first measuring coil 52 is on the side of the face of the

  measuring coil 50 facing the first mass 20.

  The second measuring coil 54 is on the side of the face of the measuring coil 50 facing the second mass 22. The first measuring coil 52 has a length such that even when the piston rod 8 is fully inserted, it exceeds at least slightly above the short-circuited coil 60,

  axially in the direction of the first mass 20.

  The second measuring coil 54 is of a length such that even when the piston rod is fully extended, it exceeds at least a little of the short-circuited coil 60, axially,

direction of the second mass 22.

  The short-circuited coil 60 consists essentially of an electrically conductive material 66 coated with insulating material and wound in a layer, preferably. It can be wound if necessary in several layers. The electrically conductive material 66 is for example an insulated copper wire. The electrically conductive material 66

  stops on a frontal force of the coil in short

  circuit 60 turned towards the first mass 20, by its first end 68 and the electrically conductive material 66 stops on a front face of the short-circuited coil 60 turned towards the second mass 22, by its second end 70. The first end 68 of the electrically conductive material 66 is connected by means of an electrically conductive member 72 to the second end 70 of the electrically conductive material 66. The electrically conductive part 72 is for example a copper wire

covered with plastic material.

  The supply coil 50, the first measuring coil 52 and the second measuring coil 54 are connected by a cable 74 to an electronics 76. The cable 74 consists of several electrical conductors, each time two conductors are connected to the coil 50 and the two measuring coils 52, 54. The electronics 76 supplies the supply coil 50 with supply voltage by means of the cable 74. A first measurement voltage induced in the first measurement coil 52 can be sent by the cable 74 into the electronics 76. A second measurement voltage induced in the second measuring coil 54 can also be sent via the cable 74

in electronics 76.

  As a result of the supply voltage applied to the supply coil 50, a supply current flows into the supply coil 50. The supply voltage is an alternating voltage with a sinusoidal pitch preferably. The supply current in the supply coil 50 causes a magnetic field

  alternative. This induces in the coil in short-

  circuit 60 a voltage. But this voltage is short-circuited. The short-circuit current flowing through it flows through the entire material winding

  electrically conductive 66 of the short-circuit coil

  circuit 60 and in turn produces over the entire length of the coil short-circuit a magnetic field. The current flowing in the electrically conductive material 66 of the short-circuited coil 60 induced in the first measuring coil 52, following the path of the short-circuiting coil 60 in the first measuring coil 52, a first measuring voltage. The current flowing in the electrically conductive material 66 also induces in the second measuring coil 54 following the immersion path of the shorting coil 60 in the second measuring coil 54, a second measuring voltage. The first measurement voltage and the second measurement voltage represent a measurement of the position of the short-circuit coil 60 with respect to the protective cap 10, thanks to the supply coil 50 and to the two measurement coils 52, 54. The first and the second measurement voltage can be evaluated by means of the electronics 76 in known manner, if necessary they can be displayed and / or injected in a control loop as a control loop.

than real value.

  It is particularly advantageous that the short-circuited coil 60 can be used everywhere and that it is not necessary to go out of

  cable or other part of the coil shorted 60.

  The fully shorted coil can be molded into a plastic material and thus optimally protected from environmental influences. The arrangement of the supply coil 50, the two measuring coils 52, 54 and the coil

  short circuit 60 is only given as an example.

  Naturally, it would also be possible to place the short-circuited coil 60 on the protective cap 10 and the supply coil 50, as well as the two measuring coils 52, 54 on the outer jacket 56 of the outer cylinder 4. However, advantageously the coils 50, 52, 54, so that one can have a simple and trouble-free connection between the electronics 76 and the coils 50, 52, 56, thanks to the cable 74. It is particularly favorable dene no it is necessary to have a cable going to the short-circuited coil 60. Thus, it is possible to use the coil in short circuit advantageously and advantageously on parts where the introduction of a

  cable would be problematic or impossible.

  The supply coil 50, the first measurement coil 52, the second measurement coil 54,

  cable 74, electronics 76 and the coil in short.

  circuit 60 together form a stroke measuring device. The first mass 20, the piston rod 8, the damping piston 6, the protective cap 10 with the coils 50, 52, 54 are stable with respect to each other and can therefore be considered as a body. The inner cylinder 2, the outer cylinder 4, the second mass 22 and the short-circuited coil are also immobile with respect to each other and can therefore be considered, like another body.-The two bodies are part of a device. The two bodies of the device can slide relative to each other. With the stroke measuring device of the invention, it is possible to grasp the position of a

  of the two bodies in relation to each other.

  In the embodiment of the invention, one of the bodies moves relative to the other body, so that the distance of the coil shortcircuit with respect to the coils 50, 52, 54 remains substantially constant. This means that the depth of penetration changes but that the spacing 64 remains constant. But it is also possible to arrange the coils 50, 52, 54, 60 on the two bodies, so that the displacement of one body relative to the other does not change the depth of penetration, but changes the spacing the surface of the short-circuited coil 60 opposite the supply coil 50 and / or the first / second measuring coil 52 or 54. In this case also the first and / or the second second measurement of voltage and the electronics 76 can determine

the spacing of the two bodies.

  Instead of two measuring coils 52, 54, it is also possible to use only one of the measuring coils 52, 54. If only the measuring coil 52 is used, the cylindrical portion 48 of the protective cap 10 may be shorter than in the case of use of two measuring coils 52, 54. It is possible to have either the supply coil 50 or one of the measuring coils 52, 54 so that it always surrounds

the coil shorted.

  For two measuring coils 52, 54, it is advantageously possible to use the difference of the two measurement voltages to make

subsequent exploitation.

  The supply coil and the two measuring coils 52, 54 can be connected together in a known manner with the electronics 76, as shown for example on page 190 in the "Manual of electrical measurement of mechanical quantities" of 1967 by Christoph Rohrbach. In this case instead of the short-circuited coil of the invention 60, a soft magnetic iron core is used. Rohrbach'indicates for his stroke measuring device shown, page 190, that a disadvantage is a low coefficient of efficiency. If the soft magnetic iron core of the stroke measuring device indicated by Rohrbach is suitably replaced by the short-circuited coil 60, the coefficient of efficiency and the range of linearity can be substantially improved. Thus it is advantageously possible to choose the spacing between the short-circuited coil 60 and the other coils 50, 52, 54 to a high enough value and still obtain sufficiently large measuring voltages and well

  operable in the measuring coils 52, 54.

  A particular advantage of the stroke measuring device of the invention is that a larger gap 64 can be chosen than in the known stroke measuring device, while still obtaining

  signals large enough and exploitable enough.

  The spacing 64 may be chosen substantially greater than 6 mm. The possibility of being able to widely dimension, the spacing 64 significantly simplifies the construction, manufacture and choice of materials to use, especially for a damper. Small radial displacements of the protective cap 10 with respect to the cylinders 2, 4 can not, or almost not, distort the measurement result thanks to

  the distance 64 relatively important.

  Even for a large spacing 64, the measurement voltages induced in the measuring coils 52, 54 over the entire measured travel, which corresponds for example to the stroke of the shock absorber piston, are

almost linear.

  For an appropriate frequency of the supply voltage of the supply coil 50, the temperature has little or no influence on the measurement result. The appropriate frequency depends on the nature and realization of the coils

, 52, 54, 60.

  For the stroke measuring device of the invention, strokes with a small influence of temperature can be measured without contact and very quickly. Food and exploitation is

  possible with commercial integrated circuits.

  The stroke measuring device according to the invention can be used in any device in which two bodies slide relative to one another and whose relative position relative to each other must be identified. The stroke measuring device according to the invention is not limited only to an application to dampers. In particular, the stroke measuring device can be used for all types of spring struts, for example struts with pneumatic elements,

Claims (1)

1) Stroke measuring device of a set of two bodies slidable to detect the position of one of the bodies relative to the other body, wherein a part of the stroke measuring device surrounding several coils is linked to one of the two bodies, characterized in that the other part respectively connected to the other body of the stroke measuring device surrounds a short-circuited coil (60). 2 ') stroke measuring device according to claim 1, characterized in that a part of the stroke measuring device comprises a supply coil (50) and a measuring coil (52, 54).   32) Measuring device according to claim 1, characterized in that a portion of the measuring device surrounds a supply coil   (50) and two measuring coils (52, 54).