GB2275752A

GB2275752A - Cleaning large structures

Info

Publication number: GB2275752A
Application number: GB9404346A
Authority: GB
Inventors: John Beavis
Original assignee: BOURNEMOUTH UNIVERSITY HIGHER
Current assignee: BOURNEMOUTH UNIVERSITY HIGHER
Priority date: 1993-03-06
Filing date: 1994-03-07
Publication date: 1994-09-07
Anticipated expiration: 2014-03-07
Also published as: GB2275752B; GB9404346D0; GB9304626D0

Abstract

A device (10) for cleaning structures such as buildings, vehicles and sculptures, comprises a liquid-supply means having an outlet nozzle (12) from which a jet of liquid (A) can be expelled; a first transducer means (16) which is located in the liquid-supply means and operable, under the control of a processing means (22), to create ultrasonic waves in the liquid flowing towards the outlet nozzle (12), the device, in use, being positioned in the vicinity of a macroscopic structure (20), which is to be cleaned, such that a jet of liquid (A) expelled from the nozzle impinges upon the macroscopic structure (20), the device further comprising a second transducer means (46) which is responsive to, and provides a signal indicative of, the wave energy in the liquid reflected from the macroscopic structure, the processing means (22) controlling the first transducer means (16) in response to said signal. In use the signal received by the second transducer may be used to detect incipient damage in the surface being cleaned and thence to limit the power output of the first transducer to prevent surface erosion. <IMAGE>

Description

A DEVICE FOR CLEANING MACROSCOPIC STRUCTURES The present invention relates to a device for cleaning macroscopic structures and is of particular, but not exclusive, applicability to situations in which the minimisation of even minor damage to the structure to be cleaned is of paramount importance.

In the context of the specification, the term 'macroscopic' is intended to mean structures of relatively large dimension including buildings, bridges, vehicles and sculptures.

Current approaches to cleaning such macroscopic structures are either extremely time-consuming, for example, using water jets and mists or cause surface destruction, for example, using abrasives and corrosive reagents.

It is an object of the present invention to improve not only the efficiency of the cleaning process but also substantially reduce the risk of surface damage during the cleaning process.

To this end, the present invention provides a device for cleaning macroscopic structures, the device comprising a liquid-supply means having an outlet nozzle from which a jet of liquid can be expelled; a first transducer means which is located in the liquid-supply means and operable, under the control of a processing means, to create waves in the liquid flowing towards the outlet nozzle, the device, in use, being positioned in the vicinity of a macroscopic structure, which is to be cleaned, such that a jet of liquid expelled from the nozzle impinges upon the macroscopic structure, the device further comprising a second transducer means which is responsive to, and provides a signal indicative of, the wave energy in the liquid reflected from the macroscopic structure, the processing means controlling the first transducer means in response to said signal.Preferably, the processing means is operable to analyse said signal so as to detect incipient damage to the macroscopic structure. Once incipient damage is detected, the processing means limits the power output of the first transducer means thus preventing erosion of the surface of the structure.

In one preferred embodiment of the invention, the first and second transducer means may be embodied in a single transducer, which functions in one instant as the first transducer means and transmits wave energy to the liquid, and in the next instant as the second transducer means and detects reflected wave energy in the liquid.

In accordance with the invention, the liquid is preferably water possibly, in certain applications, including surfactants or other materials for promoting cleaning. The ultrasonic energy may be used to promote reaction between substances in solution in the liquid of the jet and contaminants on the surface of the macroscopic structure; this may have energy and environmental advantages.

Exemplary embodiments of the invention are hereinafter described with reference to the accompanying drawings, in which, Figure 1 shows a device in accordance with the invention, which is suitable for manual operation; and Figure 2 shows the device depicted in Figure 1 adapted for fully automated operation.

Referring to Figure 1, a device, generally denoted 10, in accordance with the present invention is shown, in use, cleaning a wall 20 of a macroscopic structure such as a historic building. The device 10 includes a liquid-supply means, which for reasons of diagrammatic simplicity is not shown in full, having an outlet nozzle 12; suitably the nozzle 12 is about 20 cm in length.

A stream A of water under pressure enters the nozzle 12 from the unshown portion of the liquid supply means via inlet port 14 suitably in a side wall of the nozzle 12. The outlet nozzle 12 has an outlet port 15 through which a jet 17 is ejected. The jet 17 may suitably be of circular cross-section of about 1 cm diameter.

A vibrator 16, serving as both the first and second transducer means, is located in the nozzle 12 at an end portion of the nozzle 12 opposite the outlet 15 and is arranged to direct the ultrasonic beam through the outlet port along the jet 17. The vibrator 16 is coupled to a processing means which is generally denoted 22.

The processing means 22 includes a high frequency, (ultrasonic) pulse source 24 capable of driving the vibrator 16, a receiving means 26 for monitoring the vibrator's 'free-running' movement (as explained hereinafter) and a control unit 28 to coordinate the operation of the pulse source 24 and the receiving means 26. The pulse source 24 is conveniently variable with respect to amplitude, duration and duty cycle, and is capable of driving the vibrator 16 at frequencies within a range of typically 0.01 to 10 MHz; suitably the pulse source may operate at a frequency of about 1MHz with a power output of about 200 W. The characteristics of the pulse train generated by the pulse source 24, and hence the power output thereof, are controlled by the control unit 28.In the intervals between pulses, the control unit 28 actuates the receiving means 26 which monitors the dynamic behaviour of the vibrator 16. It will be appreciated that during the inter-pulse intervals the vibrator 16 may be considered to be 'free-running' as there is no external, electrical driving signal being applied thereto. The duty cycle of the pulse train is selected to optimise cleaning efficiency, whilst giving sufficient time for echo detection.

In operation, the under water pressure entering the nozzle 12 via inlet port 14 is subjected to the high frequency, ultrasonic oscillations of the vibrator 16 driven by the high frequency source 24, whereby ultrasonic waves are created in the water heading for the outlet port 15. The resulting jet of water expelled from the nozzle 12 impinges upon the wall 20 and the ultrasonic wave energy in the jet is dissipated at the surface of the wall 20, thereby to promote the cleaning thereof. The wave energy dissipated at the wall 20 can typically be in the region of 10 to 1000W. The vibrator 16 is shaped (or some other means is used) to focus the waves at the surface of the wall 20 (or other substrate); it is therefore important to ensure that the vibrator 16 is positioned at or about the appropriate distance from the surface, in use.

The water is supplied at the inlet port 14 at a pressure sufficient only to generate a laminar, stable jet of water at the outlet port 14. At this flow rate and pressure- the energy of the jet alone is insufficient to cause damage to the surface of the wall 20. In some circumstances the water may be degassed before being supplied to the nozzle 12. The geometry of the nozzle 12 and jet are optimally configured such that the jet acts as a flexible waveguide which introduces minimal attenuation and distortion to the pulses of the pulse source 24. During the intervals between the pulses of the pulse source 24, the vibrator 16 is 'free-running', which means that it is free to move in accordance with the waves reflected from the surface of the wall 20.During these inter-pulse intervals the control unit 28 activates the receiving means 26 which monitors the movement of the 'free-running' vibrator 16, and thereby provides data on the reflected wave energy and hence reflectance of the surface of the wall 20. This data, once analysed, enables the incipience of wall damage to be detected.

Once incipient damage is detected, the control unit 28 modifies the characteristics of the pulse train produced by the pulse source 24 to limit the power output of the vibrator 16 and thereby prevent erosion of the wall 20.

The above embodiment of the invention is primarily intended for use as a manually operated device in which a human operator controls the relative displacement of the device 10 from the wall 20 and decides when a particular area of the wall 20 is clean.

Referring to figure 2, in which like parts have been given the same reference numerals, an automated version of the device is shown. The nozzle 12 is mounted for movement in three dimensions on a movement means in the form of a manipulator arm (not shown) which is controlled by the control unit 28 to scan a raster in the plane parallel to the surface of the wall 20. This plane will be referred to as the X-Y plane. The device 10 further includes a sensor mounted in the nozzle 12, the sensor comprising a broad-band light source 3 and a co-operating light detector 4 capable of measuring a broad band spectrum. The sensor is coupled via light detector 4 to the control unit 28 of the processing means 22.

In an initial 'learning' period, the sensor (3-4) is directed towards a precleaned portion of the macroscopic structure to be cleaned, which in this example is the wall 20, so that the control unit 28 is able to establish a spectral record or, fingerprint of what a clean portion of the wall 'looks' like.

In operation, the control unit 28 instructs the manipulator arm to move the nozzle 12 in a raster-like motion in the X-Y plane. The rate of progression of this motion is controlled so as to ensure effective cleaning is taking place. This is achieved by comparing the reflected spectrum of the portion of the wall 20 being cleaned with the recorded, pre-iearned, 'fingerprint' spectrum, the nozzle 12 not moving on from a given location until the spectra substantially match. It should be appreciated however, that the mechanism by which the wall 20 is cleaned by the automated device 10 of figure 2 is exactly as that described in relation to the manual, Figure 1, device 10. It is preferred that at each location a small amount of random movement is imparted to the nozzle 12 in the x-y plane to allow an average reflected spectrum to be obtained.

In order to compensate for the surface irregularities of the wall 20 being cleaned, it is also preferred that the data collected by the receiving means 26 is analysed by the control unit 28 to provide an estimate of the nozzle's 12 displacement from the wall 20. This estimate is then used to control the movement of the manipulator arm on the Z axis ie. an axis perpendicular to the x-y plane. Preferably the movement in the Z direction is controlled to maintain the nozzle at the optimum distance from the surface to be cleaned, so that the beam of ultrasonic energy is focused substantially at the surface, The manual, figure 1 version of the device is considered to be particularly suitable for use on surfaces of greatest shape and reflectance complexity, and highest vulnerability to damage whereas the automated, Figure 2, version of the device permits rapid unattended cleaning of medium risk three dimensional surfaces of low reflectance variation.

The present invention is particularly advantages in cleaning porous materials such as limestones, and hence is particularly useful in the cleaning of historical buildings and sculptures.

Claims

1. A device for cleaning macroscopic structures, the device comprising a liquid-supply means having an outlet nozzle from which a jet of liquid can be expelled; a first transducer means which is located in the liquidsupply means and operable, under the control of a processing means, to create ultrasonic waves in the liquid flowing towards the outlet nozzle, the device, in use, being positioned in the vicinity of a macroscopic structure, which is to be cleaned, such that a jet of liquid expelled from the nozzle impinges upon the macroscopic structure, the device further comprising a second transducer means which is responsive to, and provides a signal indicative of, the wave energy in the liquid reflected from the macroscopic structure, the processing means controlling the first transducer means in response to said signal.

2. A device as in claim 1, wherein the processing means is operable to analyse said signal to detect incipient damage of the macroscopic structure.

3. A device as in claim 2, wherein, on detecting incipient damage of the macroscopic structure the processing means limits the power output of the first transducer means.

4. A device as in any preceding claim wherein the first and second transducer means are embodied by a single transducer.

5. A device as in any preceding claim, wherein the device further includes movement means operable to move the outlet nozzle, and a sensor operable to establish when the area of the structure being impinged upon by the jet of liquid is clean and then to cause the movement means to move the outlet nozzle.

6. A device for cleaning macroscopic structures, constructed, arranged and adapted to operate substantially as here in described with reference to the accompanying drawings.

7. A method of cleaning macroscopic structures comprising procuring a nozzle, directing a continuous laminar-flow jet of liquid flowing through the nozzle towards a structure to be cleaned and imparting ultrasonic wave energy to the jet before it is expelled from the nozzle, the geometry of the nozzle and jet being so configured that the jet acts as a flexible waveguide introducing minimal attenuation and distortion of the wave energy.