GB2123952A - Apparatus for and method of measuring the evenness of a surface - Google Patents

Abstract

Apparatus for measuring the evenness of an irregular surface comprises a number of ultrasonic transmitting transducers mounted on a moving vehicle. One or more ultrasonic receiving transducers (2) are associated with each transmitting transducer and circuitry (30, 31, 32, 33 and 34) for converting received ultrasonic energy into a voltage signal, for conditioning and oomblnlng that signal with a voltage reference and for determining reflected radiation transit-time therefrom is provided. This circuitry is associated with a computer which controls transmitter operation, disables the transit-time measurement circuitry for a programmably selectable time period less than the transmission time. After this circuitry is enabled first receipt of the reflected ultrasonic energy again disables it. This mode of operation tends to ensure that the circuitry acts only on reflected ultrasonic radiation from the nearest point on the surface being measured. <IMAGE>

Description

SPECIFICATION Apparatus for and method of measuring the event ness of a surface The present invention relates to apparatus for and a method of measuring the evenness of an irregular surface, such as a road surface, or the soffit or face of a structure.

According to one aspect of the present invention, there is provided apparatus for measuring the evenness of a surface comprising a movable support, means on the support for irradiating the surface with ultrasonic radiation, spaced ultrasonic transducers on the support for receiving ultrasonic radiation after reflection from spaced points on the surface and means for affording an indication of the transit time of the radiation from the surface to the transducers to give an indication of surface evenness.

According to another aspect of the present invention, there is provided a method of measuring the evenness of a surface including the steps of irradiating the surface with ultrasonic radiation, sensing the radiation after reflection from the surface and determining the transit time of the radiation from points on the surface in order to give an indication of surface evenness.

The ultrasonic radiation may have an omnidirectional pattern generated by spark discharge between two facing pointed conductors.

In a preferred embodiment, a microcomputer controls the transmitter operation, and disables the digital transit-time measurement electronic circuitry for a programmably selectable period of time less than the shortest possible transmission time. The receiving transducer converts incident ultrasonic energy into an electrical voltage signal. The amplitude of the electrical voltage signal output from the receiving transducer is proportional to the energy of incident ultrasonic radiation. Comparison of the electrical voltage signal output from the receiving transducer is made with a preset, but adjustable, reference voltage in a voltage comparison circuit.

The first reflected ultrasonic energy sensed by the receiver and recognised by the voltage comparator occurring after excitation of the transmitting transducer and after the transit-time measurement circuit is enabled, causes the transit-time measurement circuit to be disabled. The digital transit-time value as stored in this circuit is input to the microcomputer. This mode of operation tends to ensure that the system acts only on reflected ultrasonic radiation from the nearest point on the surface being measured.

In this preferred embodiment the movable support is a vehicle the apparatus being attached to the vehicle and consisting of a number of ultrasonic distance measurement units located side by side and spaced as required, without limitation or restriction, over the whole width or the whole length or the whole height or in any other configuration over the length and width and height of the vehicle.

By way of example an inventive apparatus will now be described which is capable of measuring the - distance to the nearest point in the radiation illumin ated area, to a resolution of better than 0.01 millimetres and having a working range of greater than 1000 millimetres. The inventive apparatus will be described in the form where the distance measurement sensors are mounted on a vehicle, transverse to the vehicle. The number of measurement sensors chosen is arbitrary and non-critical.

Each measurement sensor unit will be illustrated for example purpose only, mounted equidistant from the surface under observation. The relative and absolute positions of the measurement sensors with respect to the surfaces under observation is noncritical. The description will be made with reference to the attached figures, in which Figure 1 is a vertical sectional view of an ultrasonic distance measurement transducer assembly.

Figure 2 is a diagrammatic view of the measuring apparatus mounted transverse to a vehicle, Figure 2A is a diagrammatic view of the measuring apparatus mounted surrounding a vehicle, Figures 2 and2AP correspond respectively to Figures 2 and 2A and show the vehicle of these two figures under pitch conditions.

Figure 3 is a block diagram illustrating one ultrasonic distance measurement apparatus, Figure 4 is a signal timing diagram illustrating the time relationship between the microcomputer generated signals and the electronic circuit generated signals, for an arbitrarily chosen road distance within the vertical working range of the apparatus, Figure 5 is a block diagram illustrating the arrangement of measuring apparatus comprising five distance measurement sensors.

Figure 6 is a programme flow diagram illustrating the program execution sequence for the microcomputer, in controlling and interfacing with the ultrasonic transducer units and associated electronics circuits.

Figure 7 illustrates the signal conditioning and transit-time measurement electronic circuitry suitable for interfacing to one ultrasonic receiving transducer and the microcomputer, Figure 8 illustrates variations in relative positioning of ultrasonic transmitting and receiving transducers in a practical system, and Figure 8A illustrates the positioning of three distance measurement sensor units mounted on a vehicle whereby a curvilinear surface may be measured.

Figure 1 illustrates an ultrasonic transmitting transducer 1 comprising a pair of facing pointed conductors physically attached to a rigid support plate 3. Surrounding the transmitting transducer is a sound absorbent screen 4. Two piezoelectric crystal type ultrasonic receiving transducers 2 suitabie for operation in air are attached to the support plate 3 and positioned on diagonally opposite sides of the transmitting transducer 1. One of the receiving transducers is considered as the prime (highest priority) receiving transducer, such that information regarding distance is obtained solely from it, unless the distance information thus produced is recognised to be invalid, by the microcomputer, when the distance information as provided by the second receiving transducer is taken.More than two receiving transducers 2 could be situated surrounding the transmitting transducer 1 without limit or restriction, each being allocated a priority call rating for providing distance information in the event of erroneous distance data from the prime receiving transducer.

Figure 2 illustrates the physical mounting of five (an arbitrary choice for example purposes only) separate distance measurement-sensors 5 transverse to a vehicle 7 with wheels6. Figure 2A illustrates the physical mounting of eleven (an arbitrary choice for example purposes only) separate distance measurment sensors 5 surrounding a vehicle 7A with wheels 6A. A microcomputer 8 is suitably programmed and interfaced to control and interact with the ultrasonic transducers of each distance measurement sensor unit as illustrated in Figure 3.

Each ultrasonic receiving transducer 13, 14 has its own voltage comparator 12 and transit-time measurement electronic circuitry 11. Optical isolation 10 is provided for all signal lines to an ultrasonic transmitting transducer control unit 9 and the transmitting transducer 15.

Microcomputer generated signals 16, 17are illustrated in Figure 4. The transmit signal 16 causes the ultrasonic transmitting transducer 15 to emit a burst of ultrasonic radiation. The transit-time circuit disable signal 17, when logic high, resets the time digitzation circuit to zero, and when logic zero, enables the time digitization circuit to operate until disabled by voltage comparator recognition of ultrasonic radiation incident on the receiving transducer 13, 14. The relationship between receiving transducear voltage output 18 and voltage comparator output 19 is illustrated in Figure 4.

A block schematic diagram is presented in Figure 5, of a distance measurement sensor system considered solely for illustration-of some of the various aspects of the invention with ultrasonic receiving transducer pairs 20 and their associated voltage level comparison and transit-time digitization circuits 21 interfacing to the microcomputer~22. Single ultrasonic transmitting transducers 23 with their associated control electronic circuits 24 and optical isolators 25 are illustrated with a d.c. battery power supply 26 separate and remote from the micrdcom puter and receiving transducer circuitry and power supply unit 27.

Operation of the distance sensor system is managed by the microcomputer in the way illustrated in the operational flow diagram of Figure 6. All ultraso nictransmitting transducers are caused to transmit ultrasonic radiation synchronously, this means that distance measurements are obtained by all sensors simultaneously, consequently vehicle-bounce bounce roll or pitch do not cause errors. Figures 2A and 2AP respectively correspond to Figures 2 and 2A and show the vehicles of these figures subj-ecf to asideways pitch.The angle of pitch to the road surface is referenced 6 in Figure 2P.The normal and pitch positions of the vehicle in Figure 2AP are respectively represented by the vehicle in solid and dotted outline SL and DL. Referrinq to Figure2P, all distance values for determinåtion bf everiness pur poses, are calculated from the computer drawn line C.Sideways pitch has the effect of varying the angle 6 between the reference line Rand the line T which is drawn through the top of the surface whose even- ness is being measured, and hence the angle between the reference line R and the computer drawn line C drawn by the computer through the top points TP as measured, but has no effect on the position of the measured points relative to the line C.

Referring to Figure 2AP, distance measurement sensors are positioned symmetrically around the train carriage with A corresponding to B, L to C, K to D, J to E, I to F and H to G. When pitching sideways as illustrated the distances da to:dh as measured respectively by the sensors A, L, K, J, I and H are shorter while the distances db to dG as measured respectively by B, C, D, E, F and G are corresponding ly longer. By considering each symmetrical pair of sensors separately-the effects of pitching can be tolerated.

With reference to Figure 7, the receiving transduc er's voltage signal output is conditioned and ampli fied in the operational amplifier 30 circuit and is then input to the voltage comparator 31 where it is compared with a voltage level derived from a precision voltage reference source 32. The oscillator 33 provides the time-digitizing clock signal to the transit-time digitization counter 34. Choice of oscilla tor frequency and digitization counter size determine the measured distance resolution and working range respectively. Enable/disable control of the time digi tization counter is provided through the bistable 35.

After the microcomputer-generated time delay, following transmission of a burst of ultrasonic radiation, the removal ofthe time-digitization coun- ter reset-to-zero signal, is synchronised with the enabling of the time-digitization counter. Disabling of the digitization counter is caused by the first received ultrasonic radiation, reflected from the surface under óbservation and recognised by the voltage reference circuit, this resets the digitization enable/disable bistable. The transit-time digitization count is input to the micro-computer, analysed for validity, and stored in memory before the measure ment sequence can be repeated.

The apparatus so described andillustrated p-erforms a self-calibration routine automatically and under micro-computer control, prior to measuring the evenness of a surface and at any other time as may be required. Positions of each transmitting transducer and associated receiving transducer rela tive to each other and from a smooth calibration surface are measured by a calibration test routine.

Figure 8 illustrates the positioning of three distance measurement sensor units 30 situated side by side and mounted on a vehicle 31 with the vertical distances of the receiving transducers hra1, hra2, hrb1, hrb2, hrc" hrc2 and the transmitting transduc ers hta, htb, htc above an even level surface 32.

Figure 8A illustrates the positioning of three of the distance measurement sensor units 30 as surround ing a vehicle 31 with the distances of the receiving transducers hera1, hra2, hub1, hrb2, hrc1; hrc2 and the transmitting transducers hta, htb, htc from a calibra tion structure gauge 33.

With the vehicle stationary over, under, bbside or within the calibration surface or structure the microcomputer causes each transmitting transducer, Ta, Tb, Tc, to transmit a burst of ultrasonic radiation and in the same manner as previously described for evenness measurement a digitized transit time is obtained, related to each receiving transducer - Ra1, Ra2, Rb1, Rb2, Rc1, Rc2. Comparison of each digitized transit-time value, identifies the relative position of each receiver/transmitter pair with respect to the calibration surface or structure.

The above described apparatus permits distances to be measured, with an accuracy not limited by the wavelength of the ultrasonic radiation to surfaces which may be irregular, as with many road surface types or tunnel walls or roofs.

While the forms of apparatus illustrated and described are, by way of example to explain the invention, it is to be understood that the invention is not limited to these precise forms of apparatus or method of control and that changes may be made without departing from the scope of the invention as defined in the appended claims.

Claims (16)

1. Apparatus for measuring the evenness of a surface comprising a movable support, means on the support for irradiating the surface with ultrasonic radiation, spaced ultrasonic transducers on the support for receiving ultrasonic radiation after reflection from spaced points on the surface and means for affording an indication of the transit time of the radiation from the surface to the transducers to give an indication of surface evenness.

2. Apparatus as claimed in Claim 1, in which the means for irradiating the surface comprises an ultrasonic transmitting transducer which includes facing pointed conductors and is operative to transmit ultrasonic radiation omnidirectionally by spark discharge between the two facing pointed conductors.

3. Apparatus as claimed in Claim 1 or 2, in which there are a plurality of ultrasonic transmitting transducers and a number of ultrasonic receiving transducers are positioned surrounding each ultrasonic transmitting transducer.

4. Apparatus as claimed in Claim 1,2 or 3, in which signal conditioning, voltage comparison and transit-time measurement circuitry is associated with each ultrasonic receiving transducer.

5. Apparatus as claimed in Claim 4, in which the transit-time measurement circuitry is digital.

6. Apparatus as claimed in Claim 5, in which means are provided for delaying enabling of the transit time circuitry.

7. Apparatus as claimed in Claim 6, in which the means provided for delaying are selectively programmable to give, in operation, a selectively programmable delay period less than the shortest possi bletransmission time of the radiation.

8. Apparatus as claimed in Claim 6 or 7, in which means are provided for disabling the transit-time circuitry and for permitting the transit-time value to be latched and presented as output, said means being operative after the first receipt of radiation by a receiving transducer occurring after the transittime circuitry has been enabled following transmission of such radiation.

9. Apparatus as claimed in any of claims 4 to 8, in which the signal conditioning circuitry comprises an operational amplifier, the output of which is fed to the input of a further operational amplifier in which it is compared with a voltage level derived from a voltage reference source.

10. Apparatus as claimed in Claim 8, or Claim 9 when appendant to Claim 8, in which the transit-time circuitry comprises an oscillator and a counter, the oscillator being operative to provide a time-digitizing clock signal to the counter and the oscillator frequency and counter size being chosen in dependence upon the desired distance resolution and working range respectively of the unit.

11. Apparatus as claimed in Claim 10, in which a bistable circuit is provided for enable/disable control of the counter.

12. Apparatus as claimed in any preceding claim, in which the means for affording an indication of transit-time of the radiation from the surface to the transducers comprises a computer which also operates to control operation of the associated radiation transmission and reception circuitry.

13. Apparatus as claimed in any preceding claim, in which means are provided for accommodating differences in the distances between the means for transmitting and each receiving transducer.

14. Apparatus for measuring the evenness of a surface substantially as hereinbefore described with reference to Figures 1,2, 2P, 3,4,5,6 and 7 or to these Figures with the modification shown in Figures 2A and 2AP or Figure 8 or Figure 8A.

15. A method of measuring the evenness of a surface including the steps of irradiating the surface with ultrasonic radiation, sensing the radiation after reflection-from the surface and determining the transit-time of the radiation from points on the surface in order to give an indication of surface evenness.

16. A method of measuring the evenness of a surface substantially as hereinbefore described with reference to Figures 1,2, 2P, 3,4,5,6 and 7 or to these figures with the modification shown in Figures 2A and 2AP or Figure 8 or Figure 8A.