Background Art Generally, a track vehicle such as a railway vehicle runs along a track that is already installed. Each wheel of such a railway vehicle has a tachometer that is simultaneously rotated, in which a speed of a railway vehicle can be measured by number of rotation or frequency of a tachometer.

Therefore, a technology for measuring a speed using the tachometer is cited in Korean Patent Open-Laid No. 2000-0045995 (Open-Laid Date: 2000/07/25), in which Phase Locked Loop (PLL) is described. PLL is comprised of phase detector for detecting phase difference and for converting error value of phase into voltage and Voltage Controlled Oscillator (VOC) for converting an inputted voltage into frequency and divider for dividing into pulses of number N.

This technology focuses on an increase of the accuracy of speed measurement by that the speed measurement using a tachometer can be feasible within a predetermined time at low speed range of a railway vehicle.

However, in the case that there occurs error by wear of a wheel or a slip of a tachometer, compensation is required since the error caused by wear of a wheel is accumulated with a running of a railway vehicle.

Therefore, a development of a sensor for directly measuring an actual speed of a railway vehicle or the measuring technique is required so that it can compensate periodically a method of indirect measurement using a rotation of a wheel.

Specifically, in a railway vehicle, general speed sensor is in difficulties for its application due to vibration of vehicle. Further, since many related components and machinery are installed adjacent to a wheel, it contains a problem in that an installation of a sensor for measurement is difficult.

Disclosure of the Invention Accordingly, the present invention has been made with taking the above problems occurring in the prior art into consideration, and an object of the present invention is to provide an apparatus for measuring speed of railway vehicle and method thereof in which light is emitted from a light source installed in the vicinity of a track, and a quantity of light during a time is measured using a measuring unit and a speed converter, and an actual speed of a railway vehicle running along a track can be measured in an non-contact method, and an interference with other machineries in the vicinity of the wheel can be prevented, and thus the installation of those components can be easily achieved.

Another object of the present invention is to provide an apparatus for measuring speed of railway vehicle and method thereof wherein an actual speed of railway vehicle can be measured, which utilizes on compensation for the speed measured by a tachometer that is in use at present, and thus a running status of a railway vehicle can be determined.

In order to accomplish the above object, an apparatus for measuring a speed of a railway vehicle is comprised of a light source installed in the vicinity of a track and emitting a circular beam or a linear beam, a measuring unit installed at the front or back of the train and receiving the light emitted from the light source, and a speed converter for converting a signal received from the measuring unit into a speed value of the train.

Further, the light source comprises a laser unit emitting a continuous beam, a convex lens for controlling size of the beam emitted from the laser unit, and a collimator for emitting to the train a parallel beam after being passed through the convex lens.

Herein, it is preferable that the light source is provided where no grade or turn exists for the train to run in a constant speed. Further, the beam of the light source is emitted according to an approaching signal of the train instead of a consecutive emission.

Further, the measuring unit comprises a photodiode for converting a received light i nto a n e lectrical s ignal, a s ignal a mplifier for m aking t he s ignal t ransferred from the photodiode louder, and a band pass filter for removing noises from the amplified signal and transmitting only the needed signal.

A method for measuring a speed of a railway vehicle comprises the steps of : controlling size of a continuous beam emitted from a laser unit installed in the vicinity of a track and making a parallel beam, emitting the parallel beam to a measuring unit installed on the train, and measuring a speed of the train utilizing a time reaching a maximum level of the intensity of light or utilizing the difference of time between respective maximum levels of the intensity of light at two measuring units.

Further, an actual speed measured to the train compensates for a speed measured by a tachometer that is an indirect measuring method, and a status of a running train occurring at the installed point of the measuring unit and determining by a differential intensity of light at each installation point.

Brief Description of the Drawings The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is illustrative view of an apparatus for measuring speed of railway vehicle according to the present invention; FIG. 2 is a detailed view of an apparatus for measuring speed of railway vehicle shown in FIG. 1; FIGS. 3 and 4 are graphs describing respective signal measured on a railway vehicle utilizing a circular beam according to the present invention; and FIG. 5 is graph describing a difference of quantity of a received light in respect to a running status of a railway vehicle.

Best Mode for Carrying Out the Invention This invention will be described in further detail by way of exemplary embodiments with reference to the accompanying drawings.

FIGS. 1 to 5 show an apparatus for measuring speed of railway vehicle and method thereof. As schematically shown in FIG. 1, an apparatus for measuring a speed of a railway vehicle comprises a light source 11 installed in the vicinity of a track 10, a measuring unit 12 receiving the light emitted from the light source 11, and a speed converter 13 for converting a signal received from the measuring unit 12 into a speed value of the train.

That is, the measuring unit 12 installed on the train receives a circular beam or a linear beam emitted from the light source 11. A signal from the measuring unit 12 transfers to the speed converter 13, thus measuring an actual speed of the train 14.

The light source 11, as shown in FIG. 2, comprises a laser unit 15 emitting a continuous beam, a convex lens 16 for controlling size of the beam emitted from the laser unit 15, and a collimator 17 for emitting to the train 14 a parallel beam after being passed through the convex lens 16.

Here, an actual speed of a train 14 can be accurately obtained when the light source 11 is provided at a section where a train can run in a constant speed. The section should exist with no grade or no turn. Thus, it is desirable that a

characteristic of a track 10 should be considered when choosing an installation spot of the light source. Moreover, the beam of the light source is emitted according to an approaching signal of the train instead of a consecutive emission.

The measuring unit 12 comprises a photodiode 18 for converting a received light into an electrical signal, a signal amplifier 19 for making the signal transferred from the photodiode 18 louder, and a band pass filter 20 for removing noises from the amplified signal and transmitting only the needed signal.

As shown in FIGS. 1 and 2, a continuous beam emitted from the laser unit 15 of the light source 11 is passing through the convex lens 16 so that size of the continuous beam can be controlled properly. After passing a collimator 17, the diffused beam is changed into a parallel beam to emit the train 14.

Generally, considering the running condition or size of the train 14, the size of a beam reaching the measuring unit 12 can be changed depending on a case utilizing a time reaching a maximum level of the intensity of light emitted to the photodiode 18 or utilizing the difference of time respective maximum levels of the intensity of light emitted to two photodiodes 18.

That is, in the method using a time reaching a maximum level of the intensity of light, many errors may be occurring in a measurement since the time reaching a maximum level is short when the size of circular beam is too small, and this leads a problem that getting data must be done in a fast manner. Therefore, it is most preferable that a diameter of a circular beam is more than 30mm.

Further, in the method using the difference of time respective maximum levels of the intensity of light emitted to two photodiodes 18, it gives little effect to a size of an emitting beam, and so it is proper to set a diameter of a circular beam as 5mm.

A circular beam emitted from the light source 11 enters the photodiode 18 and is converted into an electric signal. The level of an electric signal is normally low, even depending on the intensity of light. Thus, the level of the electric signal must be increased to a proper level by the signal amplifier 19.

Further, the amplified signal has much noise, and the signal should be passed through the band pass filter 20 to select only the needed signal. The selected signal is transmitted to the speed converter 13 for getting the converted speed.

FIGS. 3 and 4 are graphs describing a typical signal measured on a railway vehicle utilizing a circular beam. FIG. 3 shows a level of the intensity of light emitted to the measuring unit 12 against a time, while FIG. 4 shows a level of the intensity of light emitted to two measuring units 12 against a time.

As illustrated on the graph, the intensity of light emitted from the measuring unit 12 is displayed as a three dimensions graph, because the intensity of light is the same as the area of the circular beam emitting to the photodiode 18.

Herein, if the intensity of light is maximum, it means that all of a circular beam is emitted to the photodiode, the time is reached as the intensity of light reaches a maximum level, and a speed is obtained by the following formula: A speed of a train = a distance of a circular beam/a time reaching a maximum level of the intensity of light.

In FIG. 4, the light source 11 is installed in the vicinity of a track 10 and the train 14 runs along the track 10. Signals are caught with time difference on two measuring units 12 attached on the train 14 in a predetermined space.

Therefore, in the case of two measuring units 12, the speed can be obtained by the following formula: A speed of time = a distance between each measuring unit/time difference between each measuring unit.

The above two methods are two embodiments of the present invention, but a light source of various shapes can be adapted. As the previous description, another method can be used, in which the beam of the light source is emitted according to an approaching signal of the train instead of a consecutive emission of the beam.

Further, FIG. 5 is a graph describing the intensity of light received from two measuring units 12. The two measuring units 12 are installed at a rear of the train 14, where severe wear may occur at a wheel or a puncture happens when a rubber wheel is employed.

Each intensity of light emitting to two measuring units 12 are previously analyzed according to the extent of wear, a puncture, and a suspension defect in respect to a wheel having a measuring unit 12. Therefore, a status of the running train 14 can be estimated by the difference Al, A2 of the intensity of light.

Although preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as defined in the accompanying claims.

Industrial Applicability As described above, the inventive apparatus for measuring speed of railway vehicle and method thereof has an effect in that light is emitted from a light source installed in the vicinity of a track, and a quantity of light during a time is measured using a measuring unit and a speed converter, and an actual speed of a railway vehicle running along a track can be measured in an non-contact method, and an interference with other machineries in the vicinity of the wheel can be prevented, and thus the installation of those components can be easily achieved.

Further, the present invention has an excellent effect in that an actual speed of railway vehicle can be measured, which utilizes on compensation for the speed measured by a tachometer that is in use at present, and thus a running status of a railway vehicle can be determined.