OPTICAL SYSTEM FOR MEASURING CONTACT STRENGTH BETWEEN PANTOGRAPH AND OVERHEAD LINE

Abstract

Optical system for measuring position and acceleration of the sliding bow of a pantograph, and the contact force between the sliding bow and the catenary suspension line, comprising: at least a camera installed on the ceiling of a railway vehicle and configured so that a region containing at least a portion of said sliding bow is framed; at least a laser focused on a laser sheet arranged on a substantially vertical plane and directed towards said pantograph, said laser sheet intersecting said region framed by said camera, characterized in that said system funher comprises at least a cylindrical target installed integrally to said sliding bow, with an axis parallel to the one of said sliding bow, in a position in which said target is lighted by said laser and framed by said camera, said target being realized in material reflecting to the frequency of the light emitted by said laser.

Claims

1. An optical system for measuring position and acceleration of the sliding bow (11) of a pantograph (1), and the contact force between the sliding bow (11) and the catenary suspension line, comprising: at least a camera (21) installed on the ceiling of a railway vehicle and configured so that a region containing at least a portion of said sliding bow (11) is framed; at least a laser (22) focused on a laser sheet arranged on a substantially vertical plane and directed towards said pantograph (1), said laser sheet intersecting said region framed by said camera (21): and wherein said system further comprises at least a target (111) installed integrally to said sliding bow (11) in a position in which said target (111) is lighted by said laser (22) and framed by said camera (21), said target (111) being realized in material reflecting to the frequency of the light emitted by said laser (22), and wherein said target (111) is cylindrical and installed with axis parallel to the one of said sliding bow: and wherein said system further comprises at least another cylindrical target (112) installed integrally to the support (12) of said sliding bow (11), in a position in which said further target (112) is lighted by said laser (22) and framed by said camera (21).

2. (canceled)

3. The optical system according to claim 1, wherein said at least two cylindrical targets (111) are installed integrally to the said sliding bow (11), said targets being lighted by laser sheets, respectively, and in that both said laser sheets intersect said region framed by said camera (21).

4. The optical system according to claim 1, wherein said at least two cylindrical target (111) are installed integrally to the said sliding bow (11), said targets being lighted by laser sheets, respectively, and in that said system further comprises at least two cameras (21), each one of said laser sheets intersecting a region framed by at least one of said cameras (21).

5. The optical system according to claim 1, wherein said laser emits near infrared at a wave length between 800 and 850 nm.

6. The optical system according to claim 1, wherein said camera (21) is provided with a band-pass interferential filter, centered on the frequency of said laser (22).

7. The optical system according to claim 1, wherein said camera (21) is a linear sensor camera.

8. The optical system according to claim 1, wherein said camera (21) is a matrix sensor camera. cm 9. A method for measuring the movement of the sliding bow (11) of the pantograph (1) of a railway vehicle and its acceleration by using the device according to any one of the preceding claims, comprising the steps of: a) constraining to said pantograph (1) at least a cylindrical traget (111) with axis parallel to the pantograph sliding bow; b) lighting said pantograph (1) with a laser light source (22), focused on a laser sheet (221) positioned in a vertical plane intersecting said target (111); c) acquiring with a linear camera (21) or a matrix camera (23) a plurality of images of the region containing said pantograph (1) referred to following time instants; d) identifying in each one of said images the pixels relating to the position of said target (111), and so, determining the height to the ceiling of the train of said target (111) and said sliding bow, in each one of said following time instants; e) calculating speed and acceleration of said sliding bow (11) on the basis of the position in time of the same, measured at point d.

10. The method according to any one of claim 9, further comprising the steps of: comprising the steps of: f) determining position and acceleration of the sliding bow in following time instants by means of the method according to claim 9; g) calculating, for each considered time instant, the force exerted by the suspension spring (13) of said sliding bow (11) in function of the position of the same, determined at step f; h) acquiring the speed of the railway vehicle and determining the aerodynamic force acting on said pantograph (1) in function of said speed in each time instant; i) calculating, for each time instant, the inertia force acting on said sliding bow (1) in function of the acceleration calculated at step f; j) calculating the force exchanged between sliding bow (11) and catenary suspension line in each time instant as the sum of the forces calculated at steps g, h and i.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Some preferred embodiments will be described in detail in the following, with reference to the appended FIGS. 1 to 6.

[0021] In FIGS. 1, 2 and 3 it is shown a first embodiment of the invention comprising a linear sensor camera, in an axonometric, section and detail view, respectively.

[0022] In FIGS. 4 and 5 it is shown a second embodiment of the invention, comprising a matrix sensor camera;

[0023] in FIG. 6 it is shown an illustrative geometrical schema describing the measuring principle.

[0024] In FIGS. 7 and 8 there are shown two embodiments, known at the state of the art.

DETAILED DESCRIPTION OF THE INVENTION OR OF THE PREFERRED EMBODIMENTS

[0025] In FIG. 1 it is shown an axonometric view of a first preferred embodiment of the device according to the present invention. In particular the pantograph and the device are shown in their mutual positioning. Only for graphical clarity, it is not shown the ceiling of the railway vehicle to which they are both constrained integrally. As it is shown in FIG. 1, the pantograph (1) comprises a sliding bow (11) and a support (12) of the sliding bow. The sliding bow (11) is provided, in the surface facing upwards, with a conductive strip, called sliding, which, in working conditions, is in contact with the catenary suspension line. The sliding bow (11) and its support (12) are connected by means of a spring suspension (13).

[0026] In order to increase the intensity of light reflected towards the camera, on the pantograph (1) at least a cylindrical target (111) is installed integral to said sliding bow (11), and possibly also a target (112) integral to the support (12). The targets are positioned with their axis in parallel to said elements of the pantograph (1). The targets (111, 112) are realized in reflecting material to the frequency of laser (22) (whose usage is shown in the following), and preferably in stainless steel.

[0027] The device for measuring the pantograph position comprises a camera (21) and a laser (22). The optics of the laser (22) is such that the same is focused on a laser sheet whose plane (221) is shown in dotted line in FIG. 1. In FIG. 1 it is also shown in solid line the opening angle in the field of view (211) of the camera (21). The opening angle shown in FIG. 1 is schematically the one obtainable with a linear sensor camera and respective optics. In FIG. 4 it is schematized the usage of a camera with field of view (231) with greater opening angle, typically obtainable with a matrix camera (23) and respective optics.

[0028] The laser (22) is directed towards the pantograph (1) and the laser sheet (221) is arranged on a substantial vertical plane. With reference to the camera (21), its position has to be such that, at the pantograph the plane lighted by the laser sheet (221) is contained inside the field of view (211) of the camera (21).

[0029] In this way, the camera frames the portion of the pantograph (1) lighted by the laser, and in particular the cylindrical target (111) lighted by the laser. Preferably, laser (22) and camera (21) are positioned close to each other, so that they are easily installed pre -assembled inside a unique container (not shown in figure). The laser (22) can be arranged next to the camera (21), as it is shown in FIG. 1, or it can be positioned over or under the same. As an alternative, is can be used a setup of kind shown in FIG. 4, in which laser and camera are spaced with respect to each other.

[0030] The utility of cylindrical targets (111, 112) is clear with reference to the schema of FIG. 6, which shows a side view in which laser (22) and camera (21) are schematized as circles, and the cylindrical target is shown in a first (111) and a second position (111). It is clear from the image that in all the positions the target (111) can take after that the pantograph is lowered, there exists an optical laser-target-camera path in which the camera receives the laser light by direct reflection. In fact, by joining the target centre (111) with the middle point of the joiner of the positions of laser (22) and camera (21) it is individuated on the outer circumference of target a point such that the laser light is reflected in specular manner towards the camera, thus maximizing the intensity of radiation which arrives on the camera.

[0031] Always with reference to FIG. 6, it is clear that the point for which the laser light is reflected directly towards the camera is displaced on the outer surface of the target while varying the position of pantograph. This error is however absolutely systematic (it is repeated identically in all the pantograph lifting/lowering cycles), and so it can be eliminated with a simple preliminary procedure of calibration.

[0032] After describing the system geometrical configuration, it is now possible to describe its optical features.

[0033] As it is known, the laser is a monochromatic light source, this meaning that it emits light in a very limited spectral interval. Preferably, the laser (22) used in the system according to the present invention emits near infrared, and more preferably at wave length between 800 and 850 nm, to which the intensity of the solar light spectrum is lower.

[0034] The camera (21) is preferably provided with a bandpass interferential filter centred on the laser frequency, whose function is to filter the whole light arriving with frequencies outside the allowed band, and so, to exclude almost all the solar radiation as well as the radiation coming from artificial light sources.

[0035] Therefore, to the sensor of the camera there will arrive only: [0036] the laser light reflected in specular manner by the pantograph;

[0037] the portion of solar radiation (when present) comprised in the band of wave length allowed by the filter.

[0038] By calibrating the laser power so that the first one of the two contributions enlisted is sensibly greater (at least one order of magnitude) than the second one, the sensor of the camera will detect only a peak of signal at the position of the pantograph, regardless of the environmental light conditions where it works.

[0039] Whether it is used a linear sensor camera or a matrix sensor camera, the obtained image has a very high signal/noise ratio, and it allows to determine immediately the position of target (and of pantograph).

[0040] In FIGS. 4 and 5 it is shown a second embodiment for the present invention, in which it is used a matrix camera (23) instead of the linear camera (21) . The field of view (231) of the matrix camera has an opening angle sensibly greater than the one of the linear camera. For this embodiment all the just described considerations are valid.

[0041] In addition, it is to be specified that the described device comprises acquiring and processing means of data detected by the camera, as well as control means of the camera and laser, conveniently installed on the train.

[0042] There are described also other embodiments of the device according to the present invention. In fact, in order to identify possible rotations of pantograph, on the sliding bow there can be installed two cylindrical targets, on which respective laser sheets are focused. The same can be done possibly for the support. The images of the region containing the two cylindrical targets can be acquired by means of two linear cameras, each one paired with a respective target and a respective laser sheet, or by means of a camera with matrix sensor and optics configured so that the whole region of interest is framed. In this way, it is possible to individuate the height of the sliding bow in two distinct points, and so, to identify a possible rotation of the same.

[0043] In FIG. 9 it is further schematized the geometry of a preferred embodiment of the device. The target (111) is made up of a highly reflecting cylinder, preferably realized in polished stainless steel. The section of the cylinder is shown in FIG. 9 with a very much greater dimension than reality, to highlight the behavior from an optical point of view. The surface features of the cylinder make highly predominant the effect of specular reflection with respect to diffusion, so the target (11) is an almost perfect reflector for which the Snell reflection law is applied. The circular section guarantees that, among the plurality of rays (226, 227), emitted by the laser (22), there is surely a ray (226) which is reflected in specular manner in a ray (228) intercepted by the camera (21).

[0044] From simple considerations of geometrical optics, it is clear that for each height of the sliding bow (11) of the pantograph, and so for each height of the cylinder (111) integral to it, there always exists, and uniquely, the ray emitted by the laser (22) reflected in specular manner in the camera (21).

[0045] With the schema of FIG. 10, it is shown that the uniqueness of the ray reflected in specular manner is a sufficient condition not to be disturbed by the sun. There are to be considered in fact the two extreme positions (111) and (111) which the target can take: at such position there will be 2 univocal rays (226) and (226) emitted by the laser 22 which will be reflected in the camera (21) through the respective rays 216 and 216. To maximize the resolution of the camera and so the precision of the measurement, the focal length of the objective (214) of the camera is chosen so that the extreme positions of the cylindrical target produce the images on the sensor (213) of the camera in the extreme points (A, B) of the same. So, it is assumed that all the rays of the laser beam not comprised between the two univocal rays (226, 226) will be projected on the points outside the sensor, and so will be not visible to the camera.

[0046] If it is considered the ray (41) emitted by the sun (4) and which is projected on the cylinder, it can be assumed, from simple considerations of geometrical optics, that, for any height of the cylinder between the extreme positions 111 and 111, such ray cannot be visible to the camera since it does not belong to the ray beam between 226 and 226. While varying the height of the sun, considering the set up of the system of interest, there is no solar ray, reflected by the cylinder, belonging to the ray beam between 226 and 226; so, the sun cannot generate in any way a disturbance signal on the camera, by reflection on the cylinder.

[0047] The unique ray of disturbance is caused by direct incidence, as it is shown in FIG. 11. In this case, the solar ray (41) is projected in the point C on the sensor of camera (21). Anyway since the cylinder moves with a time dynamics which is many orders of magnitude greater than the sun, the point C will appear practically in fixed position and so will be simply individuated and filtered by the image processing software. It is to be noted that the disturbance signal (43) of FIG. 8 is diffused by the target and produces an image moving on the sensor with the same time dynamics of target, therefore it cannot be recognized as solar reflection and so cannot be eliminated.

[0048] The present invention provides further a method for measuring the movement of the pantograph sliding bow, its acceleration and for determining the contact force between pantograph and catenary suspension line, by using the just described device.

[0049] The method for determining the position comprises the steps of:

[0050] a) constraining to pantograph (1) at least a cylindrical target (111) with axis parallel to the pantograph sliding bow;

[0051] b) lighting the pantograph with a laser light source (22), focused on a laser sheet (221) positioned in a vertical plane intersecting said target (111);

[0052] c) acquiring with a linear camera (21) or a matrix camera (23), provided with a frequency filter centered on the frequency of said laser (22), a plurality of images of the region containing the pantograph referred to following time instants;

[0053] d) identifying in each one of said images the pixels relating to the position of the target, and so, the height to the ceiling of the train of the same target, and so of the sliding bow, in each one of said following time instants;

[0054] e) calculating speed and acceleration of sliding bow on the basis of the position in time of the same, measured at point d.

[0055] In order to determine the contact force between sliding bow and catenary suspension line, it is to be considered that the same is the sum of the aerodynamic force exerted on the pantograph (function of the squared train speed and of the aerodynamic features of the pantograph), elastic force exerted by the suspension springs between sliding bow and its support (function of pantograph position and spring features) and inertia force (function of pantograph acceleration).

[0056] By knowing, by means of the method in points a) to e) the position and the acceleration of the sliding bow for each time instant and by knowing the force exerted by the suspension spring of the sliding bow in function of the position of the same, and the dependence law of aerodynamic force on the train speed, it is sufficient to acquire the speed of the train to estimate all the components of the contact force between pantograph and catenary suspension line, and so to calculate the resulting force. To do so it is needed to implement the method comprising the following steps of:

[0057] f) determining position and acceleration of the sliding bow in following time instants by means of the method according to claim 8;

[0058] g) calculating, for each considered time instant, the force exerted by the suspension spring (13) of said sliding bow (11) in function of the position of the same, determined at point f);

[0059] h) acquiring the speed of the railway vehicle and determining the aerodynamic force acting on said pantograph (1) in function of said speed in each time instant;

[0060] i) calculating, for each time instant, the inertia force acting on said sliding bow (1) in function of the acceleration calculated at point f;

[0061] j) calculating the force exchanged between sliding bow (11) and catenary suspension line in each time instant as the sum of the forces calculated at points g, h and i.