Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2000-04-25
2002-03-19
Dang, Hung Xuan (Department: 2873)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S338100, C250S340000
Reexamination Certificate
active
06359277
ABSTRACT:
This invention relates to a method and an apparatus for detecting coatings and has particular application, for example, to plain margin detectors for the detection of an acceptable plain margin that is to be joined in can production.
BACKGROUND TO THE INVENTION
A discussion of a typical manufacturing process for three-part cans, and a discussion of at least some of the problems encountered in welding a blank into a tube associated with a failure to obtain a good plain margin of unlacquered sheet, is given later with reference to
FIGS. 1
to
4
of the accompanying drawings. The reader is directed to read this text now in order to put the invention into context.
OBJECT OF THE INVENTION
It is an object of the invention to provide an apparatus and a method for detecting a coating whether that coating is wet or dry.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided an apparatus for detecting a coating on a substantially planar object which is moving in a predetermined direction relative to the apparatus, the object having a coating on at least a part of the planar surface thereof, which coating is at least partially transparent to visible radiation, the apparatus comprising:
an emitter adapted to emit a beam of substantially non-visible electromagnetic radiation having a predetermined wavelength range towards the object;
scanning means adapted to scan the beam of electromagnetic radiation in a direction that has at least a component transverse to the predetermined direction;
a sensor for detecting radiation in the predetermined wavelength range which is reflected in a specular manner by the object; and
means for determining the presence and/or absence of a coating on the object on the basis of the magnitude of specularly reflected radiation.
According to another aspect of the present invention there is provided a method of detecting a coating on a planar object which is moving in a predetermined direction, the object having a coating on at least a part of the planar surface thereof, which coating is at least partially transparent to visible radiation, the method comprising the steps of:
emitting a beam of substantially non-visible electromagnetic radiation having a predetermined wavelength range towards the object;
scanning the beam of electromagnetic radiation in a direction that has at least a component transverse to the predetermined direction;
sensing radiation in the predetermined wavelength range which is reflected in a specular manner by the object; and
determining the presence and/or absence of a coating on the object on the basis of the magnitude of specularly reflected radiation.
When embodied in a plain margin detector, this enables us to check sheets of lacquered (coated) sheet material (e.g. steel) whilst the lacquer is wet or dry, preferably when the lacquer is wet immediately after lacquering.
Thus, in practice the radiation is differentially absorbed/reflected between an uncoated region and a coated region, and the sensor is adapted in use to detect that radiation.
Preferably the sensor is an optical sensor.
Preferably the radiation is absorbed by the coating more than it is by the substrate material of the object.
Preferably the radiation is emitted at a wavelength that is at, or near enough to, the absorption wavelength of a component of the lacquer, any solvent used to apply the lacquer, or the substrate material, so that it is in use absorbed. For example, the radiation wavelength may be in the near infrared or in the ultraviolet region of the spectrum.
When in the near infrared region, the radiation wavelength may be substantially at the absorption wavelength of the C—H bond (on at least one of its absorption wavelengths). Most lacquers, e.g. phenolic lacquers, epoxy lacquers and vinyl lacquers, have C—H bonds. Steel, of course, does not (nor does any metal).
Looking for a C—H bond is a very good way of detecting whether or not there is a coating on an object, for example of detecting a plain margin and checking that the plain margin has no lacquer thereon. Conversely, it is also a good way of detecting uncoated regions in a coated object. The precise absorption wavelength of a C—H bond depends upon its environment—what structural groups are next to the C—H bond in its molecule and even to some extent what other chemicals (e.g. solvents) are present. I have found that 3.3 &mgr;m is a suitable wavelength for all, or at least a significant number of, common coating lacquers used in the production of cans. When employing near infrared radiation I can therefore use radiation of 3.3 &mgr;m, plus or minus 0.1, or 0.2, or 0.3 &mgr;m. Nevertheless, I have also found that 2.3 &mgr;m (plus or minus 0.1, or 0.2, or 0.3 &mgr;m) also works well in the near infrared region of the electromagnetic spectrum.
Alternatively, many lacquers are water-based and water absorbs strongly at 1.96 &mgr;m and this represents another very good way of detecting whether or not there is a coating on an object, for example of detecting a plain margin and checking that the plain margin has no lacquer thereon. Alternatively, it is a good way of detecting uncoated regions in a coated object. Thus, I can also employ near infrared radiation of 1.96 &mgr;m, plus or minus 0.1, or 0.2, or 0.3 &mgr;m.
Alternatively, I have found that most coating materials absorb electromagnetic radiation in the region of 200 to 360 nm, while metals do not. Thus, looking for absorption or reflection in the region of 200 to 360 nm, preferably about 254 nm because monochromatic light eliminates aberrations, is another very good way of detecting whether or not there is a coating on an object, once again for example, of detecting a plain margin and checking that the plain margin has no coating thereon. Conversely, it is also a good way of detecting uncoated regions in a coated object. We have found that the range of 200 to 360 nm is a suitable wavelength for all, or a significant number of, common coating lacquers used in the production of cans. Depending on the wavelength of radiation required, the emitter could comprise a halogen (for infrared radiation) or a low pressure mercury (for ultraviolet radiation) light source.
Alternatively, and in particular for detecting infrared radiation, I may use a solid state emitter such as a laser or a light-emitting diode (LED). A laser or an LED can have a small emitting surface area (e.g. about 1 mm
2
), which is easier to focus to a small point than is light from a large surface area. I prefer to chop the emitted and/or detected signal to amplify a narrow frequency band. This reduces background noise. An LED can be chopped electronically rather than mechanically. I prefer to chop electronically. The chopping frequency is preferably more than 50 kHz, and most preferably about 100 kHz or more. It is possible to chop this fast mechanically, but it is expensive to do so.
It is cheaper and more reliable to switch LEDs on and off electronically in order to chop the emitted signal. LEDs are also quieter than a mechanical chopper. Thus the sensor preferably has emitted signal chopping means, most preferably electronic chopping of an LED.
The scanning means may comprise a mechanical scanner, or an electronic scanner. An electronic scanner may comprise, for example an emitter and/or a sensor in the form of a linear array of emitters and/or sensors. A linear array of sensors may comprise, for example, a linear CCD device.
Preferably the scanning means is adapted to scan a beam of radiation back and forth (reciprocally), for example along a line. Preferably in use the object, such as a sheet of uncut blanks, and the detector experience relative movement during a scanning operation. Preferably the object is moved relative to the scanning means, but alternatively the scanning means may move relative to the object.
The transverse component of movement is preferably substantially perpendicular to the predetermined direction of movement of the object.
The scanning means preferably scans back and forth along a line at a frequency of at least 1 kHz, prefer
Dang Hung Xuan
Dorman Ira S.
Sencon Europe Limited
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