A METHOD AND AN APPARATUS FOR MEASURING CURVATURE AND CROSSFALL OF GROUND SURFACES

Abstract: A method and an apparatus for measuring the curvature and the slope of ground surfaces in two different directions are disclosed. Use is made of a drivable slope-sensitive unit which emits electric signals relating to the crossfall, the hilliness, the horizontal curvature and the covered road stretch and/or the velocity, by means of two electronic angle sensors for measuring the inclination of the drivable unit in and transversely of the direction of travel, and an angular-velocity gyro with its measuring direction in the vertical direction. According to the invention, the acceleration/retardation in the direction of travel of the vehicle, the velocity and the covered road stretch are measured by a pulse means provided in a non-driving wheel of the drivable unit and by a velocity measuring unit, the inclination of the vehicle relative to the plane through its ruts and/or relative to the plane of the roadway is measured by laser ranging units; and a continuous zero-point monitoring and calibration, respectively, of the angular-velocity gyro are performed by a compass.

Description: A method and an apparatus for measuring curvature and crossfall of ground surfaces The present invention relates to an apparatus and a method for measuring the curvature and the slope of ground surfaces in two different directions by means of a driv¬ able unit, as recited in the preambles of appended claims 1 and 5. Researchers and people responsible for road mainte- - nance need information especially on the crossfall, the curvature and the hilliness of roads to be able to take relevant steps e.g. in respect of public road repairs and maintenance to obtain maximum cost efficiency. Correct road maintenance means optimum bearing strength of the road and a minimum of traffic perils and environmental problems. Such optimum maintenance efficiency requires direct information on the crossfall, the curvature and the hilliness, as well as information which can be indi¬ rectly obtained by using these variables .for drawing maps so as to make it easier to locate all the variables mea¬ sured, e.g. road-surface variables. By simultaneous mea¬ suring, variables can be linked together, making it pos¬ sible, for instance, to establish the risks of aquaplan¬ ing at the end of a slope, in the presence of ruts and a slight crossfall, possibly also with small texture, increasing such risks. In road measuring contexts, such information may prove highly profitable, not only for acquiring more know¬ ledge in view of road maintenance, but also for monitoring newly-built surfaces and providing basic data for con¬ tracts in connection with the planning and construction of roads. Since all paved roads in Sweden are now measured regularly, the new variables provided by the present invention can be measured without any -substantial addi¬ tional costs. Thus, the economic benefits of the invention are the more appreciable. US-A-3,797,124 discloses a slope-measuring device which is especially designed for measuring the roadway inclination in the longitudinal and the transverse direc¬ tion and which has an electric slope-sensitive unit with a slope-sensitive pendulum suspended freely swinging in the slope-measuring direction, i.e. an inclinometer. When the inclinometer is tilted sideways, e.g. owing to the crossfall of the road, the pendulum tends to move in the direction of the crossfall, and the movement is converted by a sensor into an electric signal. European Patent Application 83100872.7 discloses a measuring device which is especially designed for measur¬ ing the roadway inclination in the longitudinal and the transverse direction by means of an electric slope-sensi- tive unit. This unit has a slope-sensitive pendulum sus¬ pended freely swinging in the slope-measuring direction and is connected to an indicating unit with a differentia transformer whose movable core forms the slope-sensitive pendulum and which is connected to an additional trans- former which, by transistors, converts the pendulum move¬ ments into proportional electric signals. Such modern eletronic angle sensors or inclinometers measure the angle to the horizontal plane, provided that they are subjected only to the force of gravity. Thus, th angles of inclination can only be correctly measured unde fairly static conditions. If mounted in vehicles driven i normal traffic, inclinometers of this type are exposed to forces of acceleration caused by the movements of the vehicle. Thus, this makes a contribution to the output signals by accelerations and retardations caused by step¬ ping on the gas or braking, cornering and so forth. It is known to employ gyro systems which as output signal give angles to the horizontal plane for determinin the horizontal curvature, the vertical curvature and the crossfall. However, also gyro-based system have their deficiencies, such as complicated handling procedures, a great need of attendance and maintenance, sensitivity to external influence and high initial costs, or alter¬ natively poor accuracy. The object of the invention is to improve prior-art apparatus and methods for measuring ground surfaces, especially the horizontal curvature, the vertical curva¬ ture, the crossfall and, in the event of map drawing, al the road position coordinates. This object is achieved in an apparatus of the typ stated in the introduction to this specification, with respect to the method by the distinctive features recit in the characterising clause of appended claim 1, and wi respect to the apparatus by the distinctive features recited in the characterising clause of appended claim 5 Further details and developments of the invention appear from the remaining claims. According to the invention, a measuring vehicle is equipped with two inclinometers, one in the direction of travel of the vehicle, i.e. the X-direction, for measuri the inclination of the ground in the X-Z plane, and one the Y-direction of the vehicle for measuring the trans¬ verse inclination or crossfall in the Y-Z plane. There i further provided an angular-velocity gyro, also termed rate gyro, with its measuring axis in the Z-direction. Also, for determining the velocity as well as the X-acc leration and the X-retardation of the vehicle, a pulse means is mounted in a non-driving wheel. To compensate for lateral swaying of the vehicle, the inclination of the vehicle relative to the plane through the ruts is measured by two laser ranging units, each measuring the distance down to a rut. Subtraction the measured values provides a value of the inclination in one or the other direction. There is further provided an angular-velocity gyro (rate gyro) with its measuring direction in the vertical direction (the Z-direction). I cornering, the rate gyro emits a signal ω rad/s. Assum- ing that the curve radius is R m and the velocity is v m/s, then ω • R = v or ω , = 1/R (1/m). Straight roa stretches then give the value 0, and the curve radii are defined in the vehicle-related plane X Y. Assuming that the rut depths to the left and to the right can be measured correctly, which presupposes that the outer laser ranging units reach out to measure groun surface without ruts, a relationship can be established between, on the one hand, the angle between the horizont plane and the plane of the unloaded road surface and, on the other hand, the horizontal plane and the plane throu the ruts. In cornering, lateral acceleration arises, whi affects the Y-inclinometer by an additive contribution and, above all, causes the vehicle to sway, thereby creating another source of error. If the Y-inclinometer gives the angle y, the actual crossfall can be obtained b α = y + k « AY, a being the actual crossfall, 2f being th deflection of the inclinometer in radians, and k being th dependence of the deflection of the inclinometer on the lateral acceleration in radians per m per second square 2 (rad/m/s ). The lateral acceleration AY is obtained 2 according to the equation AY = v /R, v being the velocity of the vehicle (m/s), and R being the curve radius (m), which according to the above formula gives AY = v • ω, ω being the signal angular velocity (r/s) of the rate gyro. The pulse means provided in the non-driving wheel emits a certain number of pulses per revolution of the wheel, e.g. 2500 pulses per revolution. A given humber of pulses corresponds to e.g. 2 m of travelled or covered road stretch. The time between such covered road stretches is established and serves to deter mine both the velocity and the acceleration/retardation. If the measured value for this time, when subtracting the time between two such covered road stretches from the pre ceding corresponding value, is negative, there is a retar dation. If it is positive, there is an acceleration. The magnitude of the value indicates the ' size of the retarda¬ tion/acceleration. The acceleration or retardation value is used as a correction for the angle, obtained with the inclinometer in the direction of travel (the X-direction to the horizontal plane, i.e. the gradient of the roadwa in the direction of travel. Also the road stretch covere can be recorded on the basis of the number of pulses, an the thus-obtained measured values are related to the pos tion on a longer stretch of road. The horizontal curvature is obtained on the basis o the angular-velocity information supplied by the rate gyro, and the velocity of the vehicle. Dividing the valu from the rate gyro by the velocity of the vehicle gives the horizontal curvature, which is reciprocal to the cur radius. The curvature of a straight road is 0, since the radius then is endless. The inclinometer measuring in the transverse direc- tion of the vehicle (the Y-direction) senses the lateral inclination of the vehicle body. The Y-inclinometer is sensitive to lateral acceleration in cornering. The cen¬ tripetal acceleration can be derived from the measured value of the rate gyro and the velocity value, and be su tracted from the measured value of the inclinometer. The results depend on the crossfall of a straight road or th superelevation in a curve. In addition, correction for t swaying of the vehicle body must be performed. It has been found that also an angular-velocity gyr gives rise to certain errors which, by the addition of measuring errors that can be added or subtracted, may cause incorrect indications, and the invention therefore includes an electronic compass for continuous zero-point monitoring and calibration of the angular-velocity gyro. For instance, a mean value of the supplied values of the angular-velocity gyro during the latest 100,000 pulses from the pulse means should, theoretically, correspond t another mean value derived from the values provided by t electronic compass during the same period of time. If no such correspondence exists, a correction is performed. Since also a compass may provide incorrect measured valu owing to local deviation, it is suggested, according to the invention, that also this deviation is used for cor¬ recting the measured values supplied by the compass. For exemplifying purposes, the invention will be described in more detail below with the reference to the accompanying drawings, in which Fig. 1 is a vertical section of half a roadway with positive crossfall, Fig. 2 is a basic outline showing a schematically indicated measuring vehicle to which the invention is applied, and Fig. 3 is a basic block diagram of an analysing unit for measuring a roadway. Fig. 1 is a section of a roadway, the left side in the Figure being closest to the middle of the road and th right side in the Figure being closest to the right verge of the road. The arrow Z indicates the vertical direction and the arrow Y indicates a horizontal plane transverse t the direction of travel. Further, CL designates the gra¬ dient of the roadway (superelevation) relative to the horizontal plane Y', and α« designates the inclination of a plane S through ruts in the roadway caused by wear. Since the depth sh of the rut to the right in Fig. 2 is greater than the depth sv of the rut to the left, the vehicle will come to be positioned at an angle of incli¬ nation c - . to the roadway B in the transverse direc¬ tion. For small values of α. and a- , fl "* α ι e (sh-sv):t, t being the centre distance between the wheels of the vehicle transversely of the direction of travel. Cornerin results in lateral acceleration which affects the asso- ciated inclinometer by an additive contribution, but also causes the vehicle to sway. By measuring the distance to the ground by means of two laser ranging units Lv and Lh to the left and to the right of the ruts, it is possible to obtain a value for the swaying of the vehicle relative to the roadway B. By measuring the same distance in the ruts sv and sh, it is possible to obtain a value for the swaying of the vehicle relative to the plane S through ruts. In Fig. 2, the four wheels of the measuring vehicl are indicated, but have not been given any reference nu bers. In the vehicle are mounted an inclinometer INK X for measuring the inclination <P of the vehicle relative the horizontal plane HP, as well as an inclinometer INK for measuring the inclination α of the vehicle in the transverse direction relative to the horizontal plane H There is further provided an angular-velocity measuring device or rate gyro RG with its measuring axis in the Z direction. An electronic compass EK measuring the angle in the direction of travel X and the angle øy in the transverse direction Y of the vehicle is arranged for monitoring and calibrating the angular-velocity gyro RG A laser measuring beam LA is further arranged for measu ing the distance down to the unrutted surface and also down to the ruts to the right and to the left (cf. Fig. 1). Moreover, a pulse means Pu, which is disposed a non-driven wheel, serves to measure the acceleration/ retardation in the direction of travel of the vehicle, well as the road stretch covered. The horizontal plane indicated by two arrows HP. The measured angle Ψ betwee the horizontal plane and the direction of travel indica the hilliness of the road, i.e. slope and rise, respec¬ tively, in the direction of travel, while a indicates t angle between the horizontal plane HP and the plane through the ruts of the measuring vehicle. Measurements are also made of the accelerations a in the transverse direction in cornering and a in the direction of trave caused by stepping on the gas and braking, respectively The values obtained are processed in a device in accordance with the basic block diagram shown in Fig. 3 The inclinometer X for measuring in the direction of tr vel provides a measured value <P, which is corrected for forwardly-directed acceleration or retardation a , and supplies a value for the inclination X in the direction travel. The other inclinometer Y produces a measured valu , which is corrected by the lateral acceleration a , and emits an output signal transmitted to a lateral-inclina¬ tion unit (not designated). This unit is also supplied with the measured values from the laser ranging units Lh and Lv to the right and to the left, via a comparator KO. A third input signal is transmitted to the lateral- inclination unit from an electronic unit E which in turn emits a value for the curve radius and to whose three inputs are connected the rate gyro RG and the compass EK, as well as one output of a velocity unit Vu, whose two inputs are connected to the pulse transducer Pu and to a clock signal CLOCK, respectively, and which also emits an output signal to a velocity indicator and a mileometer. The method and the apparatus according to the inven¬ tion make it possible to determine the accelerations affecting the inclinometers, and if the relationship acce¬ leration/inclinometer deflection is known, a correction can be performed so that the signal caused by the inclina- tion relative to the horizontal plane can be obtained in corrected form. The system according to the invention is highly pro¬ fitable in road measuring contexts, not only by providing more information on any road maintenance required, but also by enabling monitoring newly-built road surfaces and by providing basic data for contracts in connection with the planning and the construction of roads. With the invention, roads can be regularly measured at velocities adaptable to the prevailing traffic pace. Thus, measure- ments can be carried out also at motorway speeds, involv¬ ing minimum traffic hazards and environmental problems, as well as optimum durability. In addition, the system according to the invention is maintenance-friendly.

Claims: CLAIMS 1. Method for measuring the curvature and the slope of ground surfaces in two different directions, preferabl in and transversely of the direction of travel, by means of a drivable slope-sensitive unit which emits electric signals relating to the crossfall, the hilliness and the horizontal curvature, using two electronic angle sensors (inclinometers) in one direction (the X-direction) and in the other direction (the Y-direction) for measuring the angle to a horizontal plane (HP), and an angular-velocity gyro with its measuring direction in the vertical direc¬ tion (the Z-direction), c h a r a c t e r i s e d by measuring the acceleration/retardation in the direction o travel of the vehicle (the X-direction), the velocity and the covered road stretch by a pulse means provided in a non-driving wheel of the drivable unit and by an analysin unit; measuring the inclination of the vehicle relative t a plane through its ruts and/or relative to the plane of the roadway by laser ranging units; and continuously zero point monitoring and calibrating, respectively, the angular-velocity gyro by a compass. 2. The method of claim 1, c h a r a c t e r i s - e d by employing an electronic compass. 3. The method of claim 1 or 2, c h a r a c t e r ¬ i s e d by deriving a first mean value from the measured values emitted by the angular-velocity gyro during a cer¬ tain period of time, deriving a second mean value from th measured values provided by the compass during the same period of time, and comparing these mean values, and usin the difference for correction purposes. 4. The method, of one or more of the preceding claims, c h a r a c t e r i s e d by compensating the measured values of the compass for local magnetic deviation. 5. Apparatus for implementing the method of any one of the preceding claims, for measuring the curvature and the slope of ground surfaces in two different directions by means of a drivable slope-sensitive unit which emits measured values relating to the crossfall, the hilliness, the horizontal curvature and the covered road stretch and/or the velocity, including two electronic angle sen¬ sors for measuring the inclination of the drivable unit i and transversely of the direction of travel, and an angu- lar-velocity gyro with its measuring direction in the vertical direction (Z), c h a r a c t e r i s e d by a pulse means provided in a non-driving wheel of the driv¬ able unit for emitting a certain number of pulses per revolution of the wheel; laser ranging units for measur- ing the distance to the road surface in the ruts of the vehicle; and a compass for continuous zero-point moni¬ toring and calibration of the angular-velocity gyro (rate gyro). 6. The apparatus of claim 5, c h a r a c t e r i s e d in that an electric compass is employed. 7. The apparatus of claim 5 or 6, c h a r a c ¬ t e r i s e d in that laser ranging units (Lv, Lh) also are provided to the right of the right-hand rut and to th left of the left-hand rut for measuring the distance to the road surface. 8. _The apparatus of any one of claims 5-7, c h a r a c t e r i s e d by an electric unit with inputs for th output signal of the angular-velocity gyro, the output signal of the electronic compass, and the output signal o a velocity transducer. 9. The apparatus of claim 8, c h a r a c t e r i s d by a lateral-inclination unit which emits a value (Y for the crossfall of the roadway and has inputs for the output signal of a transverse-inclination inclinometer, the output signal of the electronic unit, and the laser ranging unit output signals that have been compared with one another in a comparator. 10. The device of one or more of claims 5-9, c h a r a c t e r i s e d by a first mean-value computin device for the measured values provided by the rate gyro during a certain period of time; a second mean-value com¬ puting device for the measured values provided by the com pass during the same period of time; and a comparator for these mean values.

Inventors: ARNBERG PETER W, OESTERGREN ROLAND, ARNBERG, PETER, W., OESTERGREN, ROLAND
Applicants: RST SWEDEN AB
Application year: 1991
Main classification: G01C7
IPC codes: G01C7