It is of importance to determine the non linearity or straightness of bars in many technical fields, especially for railroad rails, and the welding between these kinds of bars. Undulations can develop on railroad rails and the welds can be out of line, both of these defects decrease the comfort of the train passenger and increase the wear of rolling stock, the rails and especially the concrete sleepers for such rails.

In the European patent EP-A-107833, European patent application EP-A-0047558 and, the European patent application EP-A-0309847 measuring equipment is described for mechanical or optical measurement on such railroad rails. It is not possible with these known instruments to achieve the necessary accuracy, for instance with a resolution of 0.1 or 0.01 mm.

In the European Patents EP-A-0309847 and EP-A- 0388381 devices and methods are described for contact-free measuring along rails by means of a magnetic sensor. These known methods suffer problems especially with respect to the accuracy due to remanent magnetic fields in the rail or due to the movement of the magnetic sensor along the rail, caused by the fact that the sensor must be positioned on the rail one way or the other or otherwise held at a distance from the rail. One of the objects of the present invention to provide a apparatus and a method to easy and accurate measurements on surfaces of bars.

The present invention provides an apparatus for measuring the straightness, the deviation from the straightness or bending of the surface of a ferro magnetic bar, such as a (part of a) railroad rail, comprising of: - a first end part

- a second end part at a distance from the first end part, wherein the first and the second end parts are placed over the rail for measuring,

- a magnetic sensor that can be moved between the first and the second end part, and

- compensation means to compensate for remanent magnetic in the ferro magnetic material of the bar.

- The present invention further provides a apparatus for measuring the straightness, deviation from the straightness or bending of a surface of a ferro magnetic bar, such as (a part of a) railroad rail, which measuring device comprises of;

- a first end part

- a second end part at a distance form the first end part where in the first and the second end parts are placed over that of the rail for measuring,

- a magnetic sensor that can be moved between the first and the second end part, and

- second compensation means to compensate for the difference of the placement of the first end part and the second end part with respect to the bar or to compensate for the movement of the magnetic sensor when it travels between the first and the second end part.

The second compensation means preferably comprise reference sensors used to measure the position of the apparatus or straight edge on the rail, such that the variation in placing the apparatus on the rails can be compensated for.

The inventions also provides a method for measuring a surface of a ferro magnetic bar, wherein a first end part is placed on or in the vicinity of the bar, wherein a second end part is placed at a distance from the first part on or in the vicinity of the bar and wherein a magnetic sensor is moved between the first and the second end part. Other advantages, features and details will become apparent from the following description with reference to the appended drawings, in which:

fig. 1 shows a first preferred embodiment of the measuring system according to the present invention; fig. 2 shows a partly broken away perspective view of the measuring system of fig.l; fig. 3 is a partly schematic perspective view of the measuring system of fig. 1 and 2, fig. 4 shows detail IV from fig. 2, fig. 5 shows detail V from fig. 1, fig. 6 is a block diagram of the operation of the measuring system of the previous figures, fig. 7 shows a flowchart of the functional operation of a preferred embodiment of a measuring system according to the previous figures; and

Fig.8 shows a flowchart of a second preferred embodiment of a functional operation of a system according to fig. 1-6.

A measuring apparatus 1 (fig. 1,2,3) for measuring the straightness of a railroad rail R comprises a beam 2 cut away on the underside with a left and a right en part 3 and 4. Three shafts 5,6 and 7 are mounted between the left and the right end part, along which shafts a carriage 8 can be moved. The carriage is provided with a handle for moving the carriage to the left and right and for lifting the measuring equipment 1 from the rail R. The equipment 1 is preferably provided with for instance ball-shaped supporting elements 10,11 and 12 for a stable positioning thereof on the rail R. The carriage is provided with a display 22 (see also fig.5) to show the measuring results or other data and a keyboard 13 for entering commands to the measuring equipment 1. In a manner not shown in the drawing, the equipment 1 also has a power inlet and a data connection for data exchange with a host system such as a (personal) computer and to recharge the internal accumulator or battery of the measuring equipment. A first left reference sensor 14 and a second left reference sensor 15 are arranged (close to) the left end part 3, while close to the right end part 5 a first right reference sensor 16 and a second right reference sensor 17

are arranged. The carriage is equipped with a side measuring sensor 18 to measure the straightness of the side of the rail and a top sensor 19 to measure the straightness of the top side of the railroad rail, as well as a reference sensor 20 which generates reference values with respect to a reference cable 21 that is tied between the left end part 3 and the right end part 4 and runs freely of the measuring carriage. The shafts 5,6 and 7 that guide the measuring carriage are preferably mounted at least slightly pivotally to the respective end parts 3 and 4.

When measuring equipment 1 is placed on the rail, the reference sensors 14,15,16, and 17 determine whether the measuring system is placed correctly on the rail within certain tolerances that are related to the supporting elements 10,11 and 12. When the measuring equipment is placed correctly on the railroad rail between predetermined tolerances, then the distances of the shafts 5,6,7 from the rail is also known. By measuring continuously the distance to the straight cable 21 by means of reference sensor 20, the measuring results of sensor 20 are used to compensate for errors during the travel of the measuring carriage for instance due to the bending as result of gravity.

A tensioned cable 31 drives a potentiometer 32 in the measuring carriage 8, the output of which potmeter is used to determine the position of the measuring carriage between the left end part and the right end part, the output signal producing a sufficiently accurate measure of the measuring carriage 8 between the left and right end parts. At least one of the sensors, for instance 19, preferably has the shape of a measuring element 41 round which is arranged a relatively small electromagnetic coil 42. The internal diameter of the electromagnetic coil is for instance approximately 15 mm and the outer diameter approximately 25 mm and the height approximately 8 mm, the coil containing for instance 150 windings 43. Because the railroad rail can have a remanent magnetism that disturbs the measurements, using the electromagnetic coil allows measurement of the remanent magnetism as well as the

magnetic field that is induced into the ferro magnetic material of the rail at any point of the rail. Although the strength of the magnetic field of the remanent magnetism depends to some extent on the distance to the rail, it depends much less on the distance to the rail than the measured signal when magnetism is induced in the ferromagnetic material so that the amplitude of the disturbance of the remanent magnetism can be accurately determined, for instance using an iterative process and compensate for this disturbance when measuring the straightness of the rail. It is also possible to adapt the power current through coil 42 to compensate for the local remanent magnetism of the location where the distance to the rail is measured. The electronics for the measuring equipment 1 which are arranged on one or more boards in the measuring carriage, comprise a central processing unit 60 (fig. 6) in the form of a micro-processor, a ROM (+memory) 61 a RAM (memory) 62 provided with a back-up battery an, interface or latch device 64 that is connected to the keyboard 13, an address/data bus 65 to which the above mentioned electronic components, an analog to digital converter 66 to which the variable output of the potentiometer is connected as well as the output of a demultiplexer 67 to which via an operational amplifier 68 connected outputs of 7 measuring sensors 14-20 are connected. A D/A converter is further connected to the bus 65 and to the seven sensors (sensor 1...sensor 7) via a multiplexer 70. A RS232 interface 71 is also connected to the bus structure 65 for serial data communication to a host device (not shown) .

When a measurement is performed the user has to move the measure carriage 8 to one of the end parts, for instance the left end part 3. That a measurement can be started will be shown in the display 22 by means of the left end sensors 14 and 15. Subsequently the user can move the carriage from the left end part 3 to the right end part 4 in about 2 seconds, followed by display of the measured curve for the top and the side of the railroad rail. Such curves

can be stored in the memory of the electronics or can be zoomed in on the display 22 to show greater detail.

A measurement is preferably done for each sensor at a certain location of measuring carriage 8 in a cycle of the seven sensors 14-20 without energizing the electromagnet associated with this sensor. This provides the magnitude of the disturbing remanent magnetism for this location, enabling adjustment of the powering current for the electromagnets of each of the sensors 14-17, in order to measure the distance to the railroad rail at various positions with compensation for the disturbing field. After settling time of approximately 1 millisecond, the magnitude of the induced field is measured and the results stored temporarily in RAM. Further data manipulations can be done off-line, i.e. outside the total measuring cycle time of about 7 milliseconds as it is not possible to perform these relatively complex calculations within this short cycle time without disturbing the timing sequence of these various measurements. The measured sensor values are converted according to the software fixed in the ROM, with compensation from the various reference sensors and correction for the deviations from the distance to the reference cable, preferably by means of a polynomial function, to achieve a higher accuracy.

Fig. 7 shows the above described measuring procedure for one location in a flow chart. For numerals the reference, in the reference in the figures the following text has to be read:

70: Begin

71: switch multiplexer to the first sensor 72: Measure the reading of this sensor at zero powering current through the magnetic coil. 73: Determine the corresponding amplitude of the powering current with respect to the measured disturbance field according to a table in the ROM

74: Energize the electromagnet with the current found in the table

75: Wait one millisecond after energizing the relevant electromagnet 76: Save the reading of the corresponding sensor at the set powering current.

77: Increment the sensor number by one.

78: Did we reach a sensor number greater than 7?

79: Correct for each sensor the reading with energized magnetic coil for the measured values without energizing of the magnetic coil.

80: Determine the distance of the sensor to the rail by means of a polynomial function.

81: Correct for deviations found with respect to the reference cable.

82: Calculate the relative distance with respect to the reference sensors

83: End

A flowchart for the above described procedure is shown in figure 8 for performing a measurement along the rail. For the numbers in this flowchart the following text should be read:

84: Begin

85: Wait for the measuring carriage to reach the left end part close to the left reference sensor

86: measure the distance for all seven sensors

87: Did we reach the end position close to the right end part?

88: Wait for the next position to be reached 89: Correct the sensor readings for the measured disturbance field.

90: Calculate the distance of the sensors

91: Determine the relative distance of the measuring sensors to the reference sensors. 92: Correct for deviations measured with respect to the reference cable.

93: Show the measured curve in the display

94: End

Contact-free measuring of the surface of a bar is performed according to the invention by means of the above described preferred embodiment, while both the top and the side are measured at the same time. The measuring equipment can be easily handled and can be used both in the workshop as on-site in the field. The operation is kept as simple as possible. Measurements can be taken on-site in a couple of seconds. Preferably the memory is for this purpose dimensioned such that approximately 100 measured curves can be stored therein. The measured results can be manipulated with standard available software.

The sensors are not sensitive to corrosion on the bar to be measured and likewise insensitive to irregularities on the bar to be measured as they integrate over a distance of approx. 1cm ² . The roughness of the bar is compensated by means of the reference sensors, as are changes in the way the measuring device is placed on the rail during the performance of the measuring. The deformation of the equipment is also compensated for. It has been found in tests that a measuring speed of 1 meter per second can be achieved because the corrections and interpolations are done off-line, resulting in a measurement sample every 10 millisecond. The magnetic sensors have a resolution such that measurements are independent of small roughness of the surface of approximately 1 cm ² .

The tested accuracy is 0.03 millimeter in the horizontal direction and 0.05 mm in the vertical direction over the total measuring length of approximately 1 meter. The resolution is approximately at least 0.01 millimeter, while even smaller values were achieved during tests.

The rights applied for are in no way limited by the above described preferred embodiment. This preferred embodiment relates to measurements on a rail (bar)- it will be apparent that the present invention is not limited thereto and can also relate to measurements on other objects, such as a plate. The scope of the present invention is determined by the following claims: