HK1003580B - Method and apparatus for precisely positioning a part displaced along a rail transversely to this rail - Google Patents

Description

The invention relates to a process and device for the precise positioning, transversely to a railway track, of an organ moving along this track and in particular of a support for ultrasonic probes used for non-destructive control of the rails.

The dynamic stresses and overloads to which a railway track is subject cause the development of internal defects in the rails, such as oval spots, horizontal, transverse or longitudinal cracks, starbursts, etc.

It is important to be able to detect these defects on the track or in the workshop by a non-destructive method, so that the defective rail sections can be replaced.

The most common method of non-destructive control of the internal condition of the rails in the track or workshop is ultrasonic rail auscultation, which involves contacting the rail mushroom with transmitter, receiver or transmitter-receiver probes whose orientation is adapted to the types of defects being investigated.

The echoes of the emitted ultrasound are usually displayed on cathode ray displays. These echoes are also recorded graphically, which allows the position and nature of the defects detected to be determined. The interpretation of defects is also carried out using a digital calculator whose printer produces a direct report on the location and nature of the defects.

In the case of track control the probes may be mounted on carriages, running on the rails, and kept in sound contact with the rail metal by means of a water film.

The probes to be used and their positioning are determined by the characteristics of the defects to be detected.

For probes working with a reflected beam under non-zero incidence under the rail, the longitudinal spacing must be a function of the rail height for good reception.

In some existing designs, the lateral positioning of the probes in relation to the rail is achieved by the forced support, by a cylinder or spring, of a mechanical part rigidly attached to the probe carrier against the inner side of the rail spindle considered as a transverse geometric reference of the rail profile.

These developments have major drawbacks due to the diversity of the widths of the rails laid on the track, both due to the different types of rails laid and the different degrees of lateral wear or overwidth due to the crushing of the rails.

There are some versions of manual controls for the transverse and/or longitudinal positioning of the probes, but these are not satisfactory, since these controls must be operated by visual observation of the condition of the rail mushroom, which can only lead to an approximate result and is illusory from a certain speed of movement of the control vehicle.

US Patent 4,044,594 describes a rail auscultation device using a single probe housed in a wheel, requiring a complex control system to correct for lateral variations and angular variations of the wheel resulting from irregularities in the rail surface.

European patent application No 0 160 591 describes a process and device for the auscultation of a rail by means of ultrasonic probes sliding on the rail and in sound contact with it, whereby the position of at least one of the probes is subjected to the variations in intensity of an ultrasonic beam reflected by the lower surface of the rail sole.

US Patent 4,235,112 describes an ultrasonic device in contact with the rail and which includes an ultrasonic transmitter placed between two lateral ultrasonic receivers designed to capture the ultrasonic beams reflected by the rail's sole and core.

The use of one or two ultrasonic beams on the underside of the rail is based on the measurement of the intensity or energy of these reflected ultrasonic beams, which is not reliable. In effect the energy of these reflected ultrasonic beams is modified, disturbed by defects in the rail core and in its sole such as cracks or eclipse holes.

The document Fr 2'391'470 refers to a process and device for automatically locating and tracing a welded joint and includes for this purpose at least two ultrasonic generators placed at a certain distance from the surface of the object to be controlled. Following a mode of execution, these generators emit converging beams. Taking into account the different measured distances between the generators and the upper surface of the object to be controlled, the welded joint can be detected and tracked. This surface reflection process cannot be applied to the positioning of an organ along a rail, because the upper surface of the rail sample to be controlled therefore has an uneven and partially worn out shape which cannot be used as a surface reference.

There are other applications where it is imperative to position a towed organ along a railway track precisely transversely to the rail, whether the organ bears means of measuring, auscultating or rewiring the rail.

For all these applications the present invention provides a solution to the problem.

The process and device according to the present invention remedy the aforementioned disadvantages in that the positioning, particularly transverse, of the organ moved along the rail with respect to the axis of this rail is made independent of the intensity of the reflected ultrasonic beams and of defects in the rail core or corrosion of the lower surface of its sole, and of the shape and wear of the rolling surface of the rail spindle.

The process and device described in this invention are distinguished by the following characteristics described and claimed.

The following diagram illustrates, by way of example, the process and the transverse positioning device of a railway track auscultation probe according to the invention.

Figure 1 shows the servicing probe centred on the rail symmetry axis.

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Figure 4 is a side view of a probe carrier equipped with the transverse positioning device of the invention.

Figure 5 is a cut following the line AA of Figure 4.

Figure 6 shows the block diagram of the device according to the invention.

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The present method of positioning, transversely with respect to the longitudinal axis of a rail, of an organ moved along the rail and carrying, for example, ultrasonic sounding probes for the rail, consists in mounting on a support bearing the rail's sounding probes a probe for the determination of the transverse position of this support in relation to the rail's longitudinal axis. This determination probe consists of two transmitting-receiving probes forming an angle between them and housed in a roller sliding on the surface of the rail rolling and is brought into contact with it by means of a film of water. These transmitting-receiving ultrasonic probes each emit an ultrasonic beam of inter-exciting or impulsive pulses perpendicular to the rail. Each of these pulses is then measured in the distance from the rail, or the distance from the rail, and each of the pulses is reflected by means of a reflector.

Ultrasonic beams are made up of pulse trains, so they are intermittent when the organ is moved continuously along the rail. For measurements at a stop at several different locations on the rail these beams may have only one pulse. Furthermore these beams are synchronized, usually in such a way that the pulses from each beam are emitted simultaneously.

The time interval between a pulse from the first beam and the reception of its echo is measured and compared with the time interval between the corresponding pulse from the second beam and the reception of its echo.

The difference between these distances, or travel times, is then calculated, which is used to generate a control signal for a probe transverse positioning device or probe carrier.

This eliminates all the defects of the existing systems described in the introduction to this patent, since the measurement is independent of the energy or intensity of the beams and therefore of the internal defects of the rail and of the defects of the rail's sole, since it is no longer used for reflecting ultrasonic beams.

This method of ensuring the transverse position of the probes has the following advantages: The ultrasonic signals or beams are very little damping because the length of their path in the steel is small. Only the thickness of the rail mushroom is crossed and not the whole height of the rail, including the soul, as is the case in pre-existing devices.The inclination of the eclipse ranges is practically the same regardless of the type of rail so that the same submersion probe, i.e. two transmitter-receiver probes at a constant angle to each other, can be used on any type of rail. The centering of the probes can be done on the axis of symmetry of the rail but also, by introducing a set value different from zero, on lines parallel to this axis of symmetry.The measurement is of a differential type and is not affected by the absolute value of the travel time of the ultrasonic beams and is therefore totally independent of wear or the thickness of the rail mushroom. Since the ultrasonic beams emitted by the submersible probe are slightly divergent, a small variation in the angle formed by the eclipse range with a plane perpendicular to the plane of symmetry of the rail, i.e. parallel to its rolling surface, has no influence on the measurement result.

Figures 1 to 3 illustrate the principle of the positioning process just described.

In Figure 1 a probe holder 1 is shown sliding on the rolling table of the rail 2 sponge. This holder 1 carries the servicing probe formed by the two transmitter-receiver ultrasonic transducers 3,4 which form an angle between them approximately equal to the angle 180° - 2 α where α is the angle formed by the eclipse arms 5 with the rolling table of the rail sponge.

In this representation the support 1, and therefore the servicing probe 3,4, is centered on the axis or T-plane of symmetry of rail 2 so that the distances ABA on one side and CDC on the other side traveled by the beams of each of the probes 3,4 are equal. The times taken to travel these distances are therefore also equal and their difference is zero. In this case and as long as the set value of the servicing device from the position of the support 1 is zero, the command signal of this servicing device is zero, the probes being correctly positioned.

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So the distance AB becomes A1 B1 or $\text{GB₁ + GA₁ = AB + GA₁}$ And the distance CD becomes C1 D1 is CD minus CH where $\text{GA₁ = CH = d · sin α}$ - I 'm not .

So the round trip of a beam is equal to $\text{A₁ B₁ + B₁ A₁ =2AB + 2 · d · sin α}$ For the other beam, it's equal to $\text{C₁ D₁ + D₁ C₁}$ Or ... $\text{2CD - 2 · d · sin α}$ - I 'm not .

The difference in length between the two journeys is therefore: - What? - What? $\text{δ = 2AB + 2 · d · sin α - (2CD - 2 · d · sin α) et comme}$ $\text{AB = CD}$ $\text{δ =4 · d · sin α}$ - What? - What? and the corresponding time difference is - What? - What? ${\text{Δt = 4 · d · sin ∝/}}_{\text{V}}$ - What? - What? where V is the speed of ultrasound in the steel.

This signal Δt shall be compared with the set value determined on a case-by-case basis according to the desired position of the support 1 to create the positioning device control signal.

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Figure 7 is a time-dependent diagram of the pulses E1, E2 emitted by the two probes 3,4 and their echoes R1, R2 received after times t1, respectively t2 depending on the length of the distances L1 and L2.

It is obvious that the energy or intensity of the R echoes is of a lower amplitude than that of the pulses emitted E but this does not affect the measurement of the times t1, t2 which are not related to these energy levels.

Figure 6 shows a block diagram of the positioning and servicing device of a support 1 in relation to the axis of the rail 2 mushroom.

Carrier 1 carries the submersible 3,4 which is in sound contact with rail 2. The lengths L1 and L2 represent half the distance travelled by the ultrasonic beams emitted and received over the 3,4 probes.

This 3,4-transmitter-receiver servicing probe, coupled with a time base B, allows the determination of the t1, t2 times separating the emission of the E1, E2 pulses from their echoes R1, R2 of the probes 3,4. $\text{Δt = t₁ - t₂}$ This signal Δt is added to a control signal X by an adding device 7 which delivers the support positioning command signal (X + Δt) 1. The absolute value of this control signal (X + Δt) is compared to a threshold S by a comparator 8 which only delivers a control signal Q if the absolute value of the control signal is greater than the threshold S pre-established according to the particular working conditions of the rail state of measurement speed, resonance of the mechanical and hydraulic circuit of movement of the support 1 for example. This control signal is amplified by an amplifier 9 whose output controls a Q-servo valve 10 carrying a double action cylinder 11 fixed on one side to support 1 and on the other side to support 17 carried by the carriage rolling on the said rail and frame 18.

In addition, a linear displacement sensor 13 connected to an indicator 14 allows the transverse position of the support 1 to be controlled in relation to the frame 17 which carries it. This allows the probe to be quickly centred at the beginning of work and to be easily re-centred at work after a loss of sound contact.

Figures 4 and 5 illustrate schematically a particular design of the device for the precise positioning of ultrasonic auscultation probes on a rail in progress or in the workshop according to the invention. Carrier 1 carries a 3,4-service probe, formed as shown by two transmitter-receiver probes forming an angle between them, and 14,15 rail auscultation probes. This support 1 is mounted sliding on 16 rods located in a direction perpendicular to the T-plane of rail 2 and mounted on a frame 17 that is displaced in height relative to a guide wagon 18 by means of two 19,20 double-action cylinders.

The cylinder 11 containing the linear displacement sensor 13 controlled by the servo valve 10 allows the support 1 to be moved along the rods 16 and a 22 solid box of the wagon 18 contains the electronic part and the pressure fluid supply of the device described in reference to Figure 6, the control screen 15 and the indicator 14 being placed in the control post of a railway vehicle by which wagon 18 is towed along the railway track.

Many variations of mechanical arrangements of such a device are obviously feasible outside the scope of the claimed protection.

In particular, the support 1 could be fitted with mechanical palpations to measure the longitudinal or transverse profile of the rail of the re-wiring tools or any other element which, for its proper operation, must be positioned precisely transversely in relation to the rail.

As shown above, the invention is applicable both on the track and in a rail regeneration workshop.

Claims (11)

1. A process on the positioning of a member (1) moved along the rail (2) of a railway, transversally with respect to the plane of symmetry (T) of this rail, by emitting by means of a device (3, 4) two beams of ultrasound, detecting the echoes of these beams reflected by the rail and positioning said member (1) according to the difference in the distance travelled by the two beams, characterized in that the device (3, 4) emitting the two beams of ultrasound is placed in acoustic contact with the rail, in that the two beams of ultrasound are emitted through the rail head (2) with a predetermined angle (2α) between them, in that said predetermined angle (2α) is selected in such a manner that the two beams of ultrasound be substantially perpendicular to the fishing surfaces of the rail (5) and reflected by these surfaces (5), in that the time of travel (t₁, t₂) of each one of the two beams from their emission to the reception of the echo is determined, in that the difference Δt between said times of travel of the two beams is used to generate a first signal, the value of which is proportional to said difference (Δt) and which is influenced neither by the absolute value of the time of travel (t₁, t₂) of said beams, nor by the thickness or the wear (u) of the rail head (2), and in that this first signal is used for generating a control signal for positioning transversally said member.
2. A process according to claim 1, characterized in that the generation of the control signal for the positioning is carried out by adding a set signal (x) to said first signal.
3. A process according to claim 1 or 2, characterized in that this control signal for the positioning is compared with a threshold value (S) and in that this control signal for said positioning is used only if its value exceeds the threshold value (S).
4. A process according to claim 3, characterized in that the control signal delivered is amplified by an amplifier, the output of which actuates a valve (10) controlling the positioning of said member by means of a jack (11).
5. A process according to one of claims 1 to 4, characterized in that use is made for the centering on the plane of symmetry (T) of a rail, of at least one ultrasonic sensor sounding the rail.
6. A process according to one of claims 1 to 5, characterized in that each beam of ultrasound consists of a train of pulses.
7. A process according to claim 6, characterized in that the trains of ultrasound are synchronized.
8. A device for carrying out the process according to claim 1, characterized in that it includes a guiding carriage (18) running on the rail and provided with a support (1) which can move transversally with respect to the longitudinal axis of the rail and which carries a servosensor (3, 4) in acoustic contact with the rail; in that it includes displacement means (10, 11) for the support (1) for its transverse motion; and in that the servosensor includes two transreceivers (3, 4) forming an angle of (2α) between them, in acoustic contact with the rail, and emitting beams of ultrasound through the rail head (2) substantially perpendicularly to the fishing surfaces of the rail (5) on which they are reflected, their echoes being received by said transreceiver (3, 4); as well as a control loop (6, 9) controlling the displacement means (10, 11) for the support (1) through a signal which is function of the difference in the time of travel between the emission and the reception of the echo of the two beams of ultrasound.
9. A device according to claim 8, characterized in that the support (1) carries an ultrasonic sensor for sounding the rail.
10. A device according to claim 8 or claim 9, characterized in that the control loop carries a comparator (6) delivering a signal corresponding to the difference of the time of travel (Δt) fed to an adder (7) introducing a set value and delivering a control signal [ $\text{f(x) + Δt}$ ].
11. A device according to claim 10, characterized in that the control loop further includes an inhibitor suppressing the control signal as long as its value is less than a preset threshold value (S).