Different calibration methods are described in the literature. An example of such a method is to burry a support bar in a road section, the support bar comprising deflection sensors coupled to electronic processing means, which sensors sense the deflection of the road surface when the transportable apparatus passes or is placed over the bar. The sensed deflection is then used to calibrate the sensors in the transportable apparatus.

Another example is to place the transportable apparatus on a road section (e.g. at a test facility) with known deflection properties. The sensed deflection is then calibrated according to a known reference deflection and the output of the other sensors on the apparatus.

EP 0819196 B1 describes a deflection measurement method and equipment comprising a plurality of deflection sensors placed on a common bar, where the deflection sensors are positioned vertically on the bar. This structure has the drawback that the vehicle has to stand still in order to calibrate the deflection sensors. The drawback is that these methods are very complicated and expensive to implement. Therefore, there is a need for a calibration method that is simple and less expensive to implement. The object of the invention

The invention solves these problems by providing a calibration method, where the measuring means are mounted on a displaceable structure, and the measurement means are displaced from at least one measuring position to at least one calibration position, and the calibration process is performed continuously while the vehicle is moving. The measuring means comprise one or more deflection sensors sensing at least one reflected electromagnetic beam mitted from one or more radiation-emitting devices, according to claim 2. This enables the deflection measuring means to be calibrated on site and provides a simple and inexpensive calibration method.

According to claim 3, the deflection sensors are angled at an angle relative to vertical and connected to a central processing unit, which calculates the deflection speed based on the change in the Doppler frequency. This is done to obtain the most accurate deflection measurements. According to claim 4, the speed of the vehicle is measured using one or more speed sensors or calculated based on one or more location tracking means. One or more deflection sensors are calibrated according one or more reference sensors and a misalignment angle is calculated between the reference sensor and at least one deflection sensor, which is used for determining the deflection speed measured by that deflection sensor, according to claim 5. This enables the central processing unit to accurately calculate the deflection speed when the vehicle is moving.

According to claim 6, the vehicle or trailer unit comprises an adjustable load, the deflection speed is measured at one ore more different loads, and the misalignment error is calculated based the deflection speeds measured at different loads. This enables the misalignment error to be calculated when the deflection measuring means are placed in the measuring position. Brief description of drawings

The embodiments of the invention will now be described with reference to the drawings, in which

Fig. 1 shows the deflection measuring means and the deflection sensors placed in a measuring position,

Fig. 2 shows the deflection measuring means and the deflection sensors placed in a first calibration position,

Fig. 3 shows the deflection measuring means and the deflection sensors placed in a second calibration position,

Fig. 4 shows a deflection sensor and a reference sensor placed in a measuring position and a calibration position, and Fig. 5 shows an alternative calibration embodiment.

Description of exemplary embodiments

Figure 1 shows the deflection measuring means mounted in a trailer unit 1 , which may be coupled to a vehicle 2. Alternatively, the deflection measuring means may be mounted in the loading area of a vehicle. The vehicle or trailer unit 2 may comprise mechanical and/or electrical means for controlling the axle load, which is applied to at least one set of wheels 1'. The mechanical means may comprise an adjustable and/or displaceable load 3, which may be controlled by the electrical means which are capable of measuring the axle load. This provides optimum measuring conditions for the deflection measuring means and enables the means to measure the deflection at different loads.

The deflection measuring means may comprise at least one laser device or similar radiation-emitting device emitting an electromagnetic beam 5 towards a road surface or a rail surface. At least one deflection sensor 4, 4', which senses the deflected electromagnetic beam, may be located near the radiation-emitting device or may be integrated in the radiation-emitting device. The deflection sensor 4, 4' is used for continuously measuring any changes in the Doppler frequency of the beam, also called the Doppler effect. One or more deflection sensors may be used as reference sensors 4'. The measurements may be used for calculating the deflection speed of the road surface or rail surface in a central processing unit. The deflection sensor 4 and radiation-emitting device may be mounted on at least one support bar connected to at least one suspension unit, which both form part of a displaceable support structure 6. The support bar may be a longitudinal bar mounted in the same direction as the direction of travel. Alternatively, at least one second support bar may be mounted perpendicularly to the first bar. The suspension unit may comprise at least one actuator connected to the support bar; the actuator may be controlled by at least one motor. At least one controller, e.g. a computer or a processor, controls the operation of the motor and the actuator, so that the support bars, or alternatively the support structure 6, are continuously kept at a desired plane, e.g. the horizontal plane. At least one gyroscope, accelerometer and/or similar orientation/motion measuring device is mounted on or near the support bars and may be connected to the controller in order to determine any 3D movement of the support bar or support structure 6. The suspension unit may alternatively also comprise at least one spring element or spring-like element to reduce the load on the actuator. The purpose of the support bar is to keep the mechanical angle between the deflection sensors and the radiation-emitting devices constant.

The support structure 6 may be mounted on at least one guide structure 7 in the trailer unit 1 or the vehicle. The support structure 6 and/or the guide structure 7 may comprise mechanical means, e.g. a motor, and/or electrical means, which move the support structure 6 along the guide structure 7. This enables the support structure 6 to be moved between one or more measuring positions and one or more calibration positions.

At least one central processing unit, e.g. a computer connected to a user interface, may be coupled to the deflection sensors 4, 4' and radiation-emitting devices. The central processing unit may comprise a deflection module, which is used for calculating the deflection sensors 4, 4' based on the sensed deflection data. The central processing unit may comprise a radiation module which controls the operation of the radiation-emitting devices. The sensed deflection data may also be used for determining the bearing capacities, correct conditions, elasticity, plasticity, and other important information regarding the measured road or rail. The controller connected to the actuators in the support structure 6 may be incorporated in the central processing unit. The central processing unit may control the movement of the support structure 6.

Electronic and/or mechanical means, e.g. GPS, odometer, or similar location tracking means, may be used for continuously measuring the exact position of the deflection measuring means. The location data may be used by the central processing unit to calculate the exact driving speed of the vehicle 1 , 2. Alternatively, at least one speed sensor unit, e.g. a wheel speed sensor 8, may be used for determining the exact driving speed.

The deflection measuring means may alternatively comprise at least one angle sensor and at least one electronic/mechanical circuit for continuously measuring the angle of the radiation-emitting device. The angle sensor may be used for determining the angle at which the electromagnetic beam 5 hits the surface. In order to obtain the most accurate deflection measurements, the radiation-emitting device and the deflection sensor 4, 4' may be positioned at a predetermined angle relative to vertical. One or more sensor units 9, e.g. a wireless distance sensor, may be connected to the central processing unit, which is used for determining the distance between the road or rail surface and the deflection sensors 6 based on a reflected signal 9'. The central processing unit may raise or lower the support bar based on the determined distance, so that the optimum angle is determined. This is done in order to keep the optical elements of the deflection measuring means in focus. Figure 1 shows the deflection measuring means placed in a first measuring position, where the processing unit is operated in a measuring mode. In the measuring mode, the deflection measuring sensors 4 continuously measure the change in the Doppler frequency which is stored in a memory. The surface error may be used by the central processing unit in the measuring mode as a reference point when calculating the deflection speed. The misalignment error may be used in the measuring mode to compensate for any difference in the measuring angle between a reference sensor 4' and a particular deflection sensor 4. This enables the central processor unit to calculate the deflection speed more accurately in the measuring mode.

The same road or rail section may be measured with different axle loads or with the support structure 6 in different measuring positions. When the load 3 is adjusted and/or displaced, the deflection sensors 4 and the support structure 6 may be moved into a second measuring position, in which the impact caused by the wheel 1' surface contacting the road or rail is reduced to a minimum. When the support structure 6 is placed in different measuring positions, the same points or sections in the deflection area may be measured with different deflection sensors 4. This enables the central processing unit to calculate the deflection speed at different loads and/or to compare the data from different deflection sensors in order to create a more detailed picture of the conditions for that road or rail section. The deflection speed measured at different loads may be used to calculate the misalignment error between a reference sensor 4' and a particular deflection sensor 4. The misalignment error may be calculated based a predetermined ratio, which may be proportional or non-proportional, between the load and the deflection. This enables the misalignment error to be calculated when the deflection measuring means are placed in the measuring position. Figures 2 and 3 show the deflection measuring means placed in a first and a second calibration position, where the central processing unit is operated in a calibration mode. In the first calibration position shown in figure 2, all the deflection sensors 4, 4' are moved out of the measuring area around the wheel 1' and into an area where no deflection occurs. In the second calibration position, a portion of the deflection sensor 4 is placed outside the measuring area and the other portion of the deflection sesors 4' is placed in an area around the wheel 2' of the vehicle where deflection occurs. The deflection measuring means may then be calibrated when moving the vehicle or trailer 1 ; this enables the deflection measuring means to be calibrated on site and provides a simple and inexpensive calibration method.

In the first calibration position, all deflection sensors 4 may be calibrated according to one or more reference sensors 4". Alternatively, the reference sensors 4' may be used for calibrating a first portion of the deflection sensors 4 closest to the reference sensors 4'. The support structure 6 may then be moved into the second calibration position, where the first portion of deflection sensors 4 may be used as reference sensors when calibrating the other portion of the deflection sensors 4.

When the deflection sensors 4, 4' are placed outside the measuring area, the sensors will only sense different errors, such as misalignment of the radiation- emitting device or deflection sensors 4, 4' relative to other radiation-emitting devices or deflection sensors 4, 4', roughness of the road or rail surface, or spreading of the electromagnetic beam. The tolerances for the deflection sensors, which are due to the manufacturing process, may also be measured as an error. These continuously sensed errors may be stored in the central processing unit and be used for compensating for any differences between the deflection sensors 4 and the reference sensor 4'.

Based on these sensed errors, the central processing unit is able, to a certain degree, to determine the surface error caused by roughness of the surface, and the misalignment error caused by deflection sensors 4, 4' or radiation-emitting devices not having the same angle relative to each other. Alternatively, these errors may also be stored along with the location data, so that a more accurate deflection speed may be calculated in the measuring mode.

In the calibration mode, one or more of the deflection sensors 4, 4' may be moved into a calibration position, so that the misalignment error between at least one reference sensor 4' and at least one particular deflection sensor 4 may be determined. The processing unit may also use the sensed data for determining the misalignment error between individual deflection sensors 4 or individual groups of deflection sensors 4. In order to determine the deflection speed accurately, the angle between the deflection sensors 4 and the reference sensor 4' has to be calculated accurately. In the calibration mode shown in figure 4b, the angle α relative to vertical for each sensor 4, 4' may be determined based on the sensed speed V:

V _r = V _d -sin(α _r ) , V _m = V _d -sin(αJ , (1) where V _d is the sensed or calculated driving speed, V _r is the speed measured by the reference sensor 4', V _m is the speed measured by the deflection sensor 4, α _r is the angle for the reference sensor 4', and α _m is the angle for the deflection sensor 4. The misalignment error (the angle α _c between the reference sensor 4' and the selected sensor 4) may be determined as the difference between the two angles:

OL = α _m - α _r = arc siinn - arc sin U (2) In the measuring mode shown in figure 4a, the deflection speed may be calculated based on the sensed or calculated driving speed V _d and the misalignment error α _c between the reference sensor and the selected deflection sensor 4.

This enables the deflection speed to be determined without having to align the deflection sensors vertically and enables the deflection measuring means to be calibrated while the vehicle 1 , 2 is moving. In an alternative embodiment, the deflection sensors 4 and the support structure 6 may be placed in a combined measuring and calibration position. In this position, the support structure 6 may be positioned so that a first portion of the deflection sensors 4 is positioned within the measuring area, while the other portion of the deflection sensors 4' is positioned outside the measuring area where no deflection occurs. The first portion may be operated in the measuring mode, i.e. it measures the change in the Doppler frequency according to the deflection, while the central processing unit calculates the deflection speed. The second portion may be operated in the calibration mode, i.e. it senses the errors which are used for determining the surface error and the misalignment error.

This enables the central processing unit to calibrate the deflection sensors 4, 4' and measure the deflection speed at the same time, thus reducing the operation time required. The controller controlling the movement of the support structure 6 may switch to an alternative mode in order to provide optimum adjustment of the support structure 6 according to this combined measuring and calibration mode.

When the calibration process is completed, the deflection sensors 4 are moved back into the measuring area, and the measuring process may be started. Alternatively, the deflection measuring means may be calibrated using other known calibration methods. In an alternate calibration embodiment shown in figure 5, the deflection measuring means may be calibrated when the vehicle 1 , 2 stands still. In this embodiment, at least one rod 12 or bar is positioned below the deflection sensors 4, 4' and radiation-emitting devices. The rod 12 or bar may be placed on one or more supporting elements, which enable the rod or bar to be moved back and forth in the same plane during the calibration process. The rod 12 or bar may be moved either manually or by mechanical means. One or more additional deflection sensors 10 and radiation-emitting devices may be placed below the rod 12 or bar facing the rod 12 or bar and may be mounted on an additional support bar 11. These additional deflection sensors 10 are used for determining the movement and/or the difference in the direction of movement. The angle between the additional deflection sensors may be determined by angling and/or placing the radiation-emitting devices, so that the beams hit the same point at a predetermined distance from the radiation-emitting devices. This allows the same input signal to be applied to the additional deflection sensors 10. The deflection sensors 4, 4' may then be calibrated by moving the rod 12 or bar back and forth. The misalignment errors α _{c1 l} α _c2 , α _c3 may then be calculated as described above.