THICKNESS MEASURING APPARATUS

Abstract: The invention concerns apparatus for measuring the thickness of a double glazing unit. A thickness measuring apparatus comprises a gauge (12) having a planar lower surface (14) to be placed on a first planar surface (15) of a unit (16) to be measured, a focused light source (17), mounting means (20) for mounting the light source in relation to the gauge so that the source will transmit a focused beam (18) onto said first planar surface at a fixed angle and images (15a, 31a, 33a, 34a) of the source reflected by other substantially parallel surfaces of the unit will be formed on or in the gauge, the gauge being calibrated so that the or each reflected image formed on or in the gauge will be arranged to indicate the distance between the first planar surface and said other surfaces of the unit from which the beam has been reflected, and/or the distance between surfaces from which the beam has been reflected.

Description: THICKNESS MEASURING APPARATUS FIELD OF THE INVENTION This invention relates to a thickness measuring apparatus, most particularly for measuring the thickness of a double glazing unit but additionally useful for measuring the thickness of any sheet of transparent material. BACKGROUND OF THE INVENTION A double glazing unit comprises first and second, substantially parallel, sheets of transparent material set in a frame so that there is an enclosed space between them. Once such a unit, or even a single sheet of glass, is mounted in a window opening, it is difficult to measure its thickness. GB-A- 1 329240 describes apparatus for measuring the thickness of a sheet of glass but uses a complicated formula for calculation and would not be suitable for measuring the gap between two sheets of a double glazed unit. GB-A-1 581 948 also discloses apparatus for measuring the thickness of a sheet of glass but requires a microscope to be focused on different surfaces and the movement of the microscope to be measured . An object of the present invention is to provide a device which will easily measure the thickness both of the sheets of material and of the space between them in a double glazing unit. SUMMARY OF THE INVENTION The present invention provides thickness measuring apparatus comprising a gauge made from a sheet of clear transparent material having a planar lower surface to be placed on a first planar surface of a unit to be measured and having a surface which is calibrated, a focused light source, mounting means for mounting the light source in relation to the gauge so that the source will transmit a focused beam onto said first planar surface at a fixed angle and images of the source reflected by other substantially parallel surfaces of the unit will be formed on or in the gauge, the gauge being etched or coated to absorb the reflected light so that an image will be seen thereon, the gauge being calibrated so that the or each reflected image formed on or in the gauge will be arranged to indicate the distance between the first planar surface and said other surfaces of the unit from which the beam has been reflected, and or the distance between surfaces from which the beam has been reflected. The positions of the images may be read by an electronic light sensor and converted to a digital display provided for example by an LED (light emitting diode) read out. Preferably the laser beam is angled at 45 ° to the first planar surface so that the spacings of the reflected images on the gauge are twice the thickness measured. The zero calibration of the gauge will be in the same vertical plane as the intersection of the light beam with the first surface. In one form the mounting means and gauge are relatively slidable and, in use, the front surface of the base of the mounting is placed against the rear edge of the gauge and can be slid along it until the reflected images coincide with either a rule on the gauge or pre-marked indications of the spacings of conventional double glazed units. Alternatively the mounting means may be integral with the gauge. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of thickness measuring apparatus, in accordance with the invention, will now be described, by way of example only, with reference to the accompanying drawings which show diagrammatically the following:- Figure 1 shows a perspective view of measuring apparatus located on a double glazed unit to be measured, Figure 2 shows a side view of the measuring apparatus on a sheet of glass to be measured, Figure 3 shows a plan view of the apparatus including one form of calibration, Figure 4 shows diagrammatically the light paths in a double glazing unit and gauge, and Figure 5 shows a perspective view of an alternative form of thickness measuring apparatus. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Referring first to Figures 1 to 4 a gauge 1 2, in the form of a rectangular sheet of transparent material, for example perspex, has its planar upper surface 1 3 etched to provide a calibration indicated at 40, 41 and etched or coated to absorb and show up an image of laser light. The gauge has a planar lower surface 1 4 intended to be held flat on a planar surface 1 5 of a unit 1 6 to be measured. As seen in Figures 1 and 4 this unit is a double glazing unit. A laser source 1 7, such as a laser torch for emitting a spot or line beam of focused light 1 8, is intended to be mounted in a laser mounting device 20. The mounting device comprises a base 21 having a planar lower surface 22 and a planar front surface 23 meeting at a right angled front lower edge 24. The base 21 is integral with a holder 25 defining a tubular passageway 26 for receiving the laser source. In this example the passageway is angled at 45 ° to the lower surface 22 and has an axis which intercepts the lower edge 24. In use the mounting unit is held flat against the surface 1 5 with its front surface 23 abutting the rear surface 27 of the gauge and it can then be slid along the rear edge 27, in directions normal to the plane containing the beam, as indicated by arrow 28. The double glazing unit comprises a first sheet of transparent material 30 having an outer surface 1 5 and an inner surface 31 , and a second substantially parallel sheet of transparent material 32 having an inner surface 33 and an outer surface 34, the inner surfaces being spaced from one another by a space 35. Each of the sheets 30, 32 of transparent material has a thickness X and the width of the space is indicated as Y. As seen in Figure 4 the beam 1 8 from the laser passes through each of the surfaces 1 5, 31 , 33 and 34 and is also reflected at each surface. The reflections from each surface pass through the material of the gauge and form a spot or line image on the upper surface of the gauge these images being indicated at respectively 1 5a, 31 a, 33a and 34a. As seen in Figure 3 the upper surface 1 3 of the gauge is marked with calibrations in the form of a rule 40 and patterns of different spacings 41 commonly found in double glazing units. The laser unit can be slid along the gauge in the directions of arrow 28 until the four images align with four of the lines on the calibrations 41 . Alternatively the laser can be aligned with the rule 40 and the distances read off the rule. With the light angled at 45 ° the actual spacings between images will be twice the measured thicknesses and the gauge is calibrated accordingly. The gauge can of course be differently calibrated if the light source is angled at a different angle to the surface 1 5. By positioning the measuring device at different positions on the surface of a double glazing unit, the consistency of the air gap can be checked. The device can equally be used to measure thickness of a triple glazing unit. A modified thickness measuring apparatus 40 is shown in Figure 5. This comprises a base piece of transparent plastics material 41 having a planar base surface intended to be placed on a double glazing unit 1 6 to be measured as before. Mounted on the upper surface of base 41 is a laser light source 42 for connection to a battery 43 to produce a focused line beam of laser light angled, preferably at 45 ° , downwardly as before. The base 41 is formed with an undercut slot 45 in which a planar calibrated gauge 46 is a sliding fit, the upper surface of the gauge being etched or otherwise marked and arranged to absorb light as before. The gauge 46 is slidable in the slot to a position, in use, where its inner end 47 engages a stop 48 and in this position the zero 50 of the calibration is vertically above the line of interception of the laser beam with the lower surface of the base 41 . An aperture (not seen) is provided in the base 41 for the passage of the laser beam through the base and an elongate recess (also not seen) , in the central part of the base is formed where the reflected beams will pass through the base to the gauge 46. As in the arrangement of Figures 1 to 4, when the thickness measuring apparatus 40 is placed on a double glazing unit, four spaced reflected images of the laser beam will be seen in the central part 50 of the gauge. The calibration 51 on the gauge indicates the thickness of the upper sheet of the double glazing unit, or more specifically the distance of each of reflecting surface from the surface 1 5. The calibration 52 is arranged to indicate the thickness of the cavity. If the gauge is removed from the slot and turned through 180° and reinserted, the calibrations 53 and 54 can be used respectively to show the overall thickness of the unit with 4 mm glass and 6 mm glass. In an alternative a light sensor and calibrated electronic unit 60 is used to detect the positions of the reflected images and provide a digital readout of the measured thicknesses. A cover 61 is provided to fit over the laser source and battery to provide a protection when the unit is not in use.

Claims: CLAIMS 1 . Thickness measuring apparatus comprising a gauge made from a sheet of clear transparent material having a planar lower surface to be placed on a first planar surface of a unit to be measured and having a surface which is calibrated, a focused light source, mounting means for mounting the light source in relation to the gauge so that the source will transmit a focused beam onto said first planar surface at a fixed angle and images of the source reflected by other substantially parallel surfaces of the unit will be formed on or in the gauge, the upper surface of the gauge being etched or coated to absorb the reflected light so that an image will be seen thereon, the gauge being calibrated so that the or each reflected image formed on or in the gauge will be arranged to indicate the distance between the first planar surface and said other surfaces of the unit from which the beam has been reflected, and or the distance between surfaces from which the beam has been reflected. 2. Apparatus according to Claim 1 in which the light source is a laser source. 3. Apparatus according to Claim 1 or Claim 2 in which the focused light beam is in the form of a line. 4. Apparatus according to any of Claims 1 to 3 including light sensor means arrange to sense images on or in the gauge and provide an electronic digital display of the thicknesses being measured. 5. Apparatus according to any of Claims 1 to 4 in which the fixed angle is substantially 45 ° . Apparatus according to any of Claims 1 to 5 in which the zero calibration of the gauge is in the same plane, normal to the first surface, as the intersection of the light beam with the first surface. Apparatus according to any of Claims 1 to 6 in which the gauge and light source are relatively movable to one another to bring different scales on the gauge into line with reflected images of light from the light source.

Inventors: HAMILTON NEIL COLIN, HAMILTON, NEIL, COLIN
Applicants: HAMILTON NEIL COLIN, HAMILTON, NEIL, COLIN
Application year: 1998
Main classification: G01B11
IPC codes: G01B11