GB2348496A

GB2348496A - Method and apparatus for the detection of scratching and similar surface action to glass

Info

Publication number: GB2348496A
Application number: GB9907384A
Authority: GB
Inventors: Matthew Collins
Original assignee: Frazer Nash Consultancy Ltd
Current assignee: Frazer Nash Consultancy Ltd
Priority date: 1999-03-31
Filing date: 1999-03-31
Publication date: 2000-10-04
Also published as: GB9907384D0

Abstract

A method of detecting surface damage to a glass sheet 1 by scratching comprises one or more transducers 2, 3 in surface contact with the glass sheet. The transducers, which may be accelerometers, strain gauges or microphones, provide electrical signals in response to acoustic waves and/or vibrations in the glass. A signal processing unit 5 receives the electrical signals from the transducers and selects those characteristic of surface damage to the glass. The selected signals are fed to a response unit 6 adapted to receive such signals. The response unit activates an appropriate action if the signals exceed a preset limit. In a preferred method two transducers are placed in surface contact with the glass sheet and the signals from the two transducers are compared to eliminate background noise and false alarms. Preferably the signal processing unit selects signals having frequencies characteristic of abrasion to glass and frequencies of the resonance oscillations generated in a glass sheet.

Description

METHOD AND APPARATUS FOR THE DETECTION OF SCRATCHING AND SIMILAR SURFACE ACTION TO GLASS.

This invention relates to a method of detecting scratching and similar abrasive action on glass sheets to provide a warning of damage and apparatus for performing the method.

Apparats exists which provides a warning when glass sheets, such a windows in shops, offices and dwellings, are subject to an impact which may damage or shatter the glass.

Such apparatus is not sensitive to less energetic attacks on glass sheets although such attacks may cause considerable damage and may even lead to partial removal of the glass forming the sheet or shattering which, in the case of toughened glass, may be delayed.

The present invention detects and provides a warning when scratching and similar attacks are made on glass sheets.

According to the present invention there is provided a method of detecting surface damage to a glass sheet by scratching comprising one or more transducers in surface contact with the glass sheet which provide electrical signals in response to acoustic waves and/or vibrations in the glass, a signal processing unit adapted to receive the electrical signals, select those characteristic of surface damage to the glass and feed them to a response unit adapted to receive the selected signals and activate an appropriate action.

There is further provided apparatus comprising transducers for fitting to glass surfaces, a signal processing unit and a response unit.

The glass sheet may be plain glass, toughened glass, glass laminate, annealed glass such as used for windows or covers for apertures.

Preferably at least two transducers are used to provide electrical signals in response to acoustic waves and/or vibrations in the glass. The transducers are in contact with different portions of the glass sheet. Use of a pair of transducers permits the signals from each to be compare and assist in the elimination of background noise and false alarms. The transducers may be accelerometers, strain gauges or microphones.

Signals from the transducers are fed to the signal processing unit where they are filtered and analysed to so that only signals characteristic of surface scratching of the associated glass sheet are selected. The characteristics may include frequencies caused by direct abrasion of the glass surface and frequencies generated through resonance oscillations exited in the glass sheet.

When the selected signals reach a preset level the response unit is activated. Activation of the response unit can cause a number of actions to take place according to the location of the glass sheet. An alarm may be sounded, a distant location alerted, flood lights may be switched on and/or a surveillance camera set in operation.

In order that the invention may be clearly understood one form thereof will now be described, with reference to the accompanying drawing, in which the single figure is a block diagram of one embodiment of the apparatus for detecting surface damage to a glass sheet according to the invention.

A sheet of glass 1 has a pair of transducers 2 and 3, such as piezo electric cells, attached to points on its surface. Leads 4 carry electrical signals generated by the transducers to a signal processing unit 5. The unit 5 includes an appropriately programmed micro processor (not shown) which filters out noise from various sources such as thermal noise from components and background noise from the immediate environment. Transient signals containing characteristic frequencies known to be produced when glass of the type and dimensions of the sheet 1 is scratche are selected from the input signals if present. A preset discriminator generates an activation signal to a response unit 6 if the selected signals exceed a preset level.

By means of dedicated semiconductor devices and preprogrammed memories it is possible to combine the signal processing unit and the response unit into a single compact self-contained unit which is connected to one or more transducers and has an output lead to activate alarms, cameras etc.

Claims

CLAIMS 1. A method of detecting surface damage to a glass sheet by scratching comprising one or more transducers in surface contact with the glass sheet which provide electrical signals in response to acoustic waves and/or vibrations in the glass, a signal processing unit adapted to receive the electrical signals, select those characteristic of surface damage to the glass and feed them to a response unit adapted to receive the selected signals and activate an appropriate action.
2. The method of detecting surface damage to a glass sheet as claimed in claim 1, wherein two transducers are placed in surface contact with the glass sheet.
3. The method of detecting surface damage to a glass sheet as claimed in claim 2, wherein the signals from the two are compared to eliminate background noise and false alarms.
4. The method of detecting surface damage to a glass sheet as claimed in any of the preceding claims, wherein the transducers are accelerometers, strain gauges or microphones.
5. The method of detecting surface damage to a glass sheet as claimed in any of the preceding claims, wherein the signal processing unit selects signals having frequencies characteristic of abrasion the glass and frequencies of the resonance oscillations generated in the glass sheet.
6. The method of detecting surface damage to a glass sheet as claimed in claim 5, wherein the response unit is activated when the selected signals exceed a preset level.
7. Methods of detecting surface damage to a glass sheet by scratching as claimed in claim 1 and as herein described.
8. Methods of detecting surface damage to a glass sheet by scratching as herein described with reference to the accompanying drawing.
9. Apparatus for detecting surface damage to a glass sheet by scratching in accordance with the method of any of the claims 1 to 8 comprising one or more transducers, a signal processing unit adapted to receive the electrical signals from the transducers and select those characteristic of surface damage to a glass sheet, a response unit adapted to receive the selected signals and provide an active output.