Lamp Assembly With Filter Producing Variable Proportions of Ultraviolet and Infrared Radiation

The present invention relates to lamp assemblies and more particularly to lamp assemblies for use in the printing and coating industries for the fast drying or curing of inks and lacquers on a large variety of substrate materials. During the drying or curing process, the substrate is caused to move along a path such that successive strips of the substrate are irradiated by an elongate lamp assembly in a continuous process.

Such lamp assemblies typically use ultraviolet light generated by high-powered lamps in a reflector system.

Such systems, however, generate a considerable proportion of infrared energy, such as 60% of the total emitted radiation. Whilst this is generally beneficial in accelerating the curing process, the heat can be problematic in some applications where heat-sensitive materials are being handled.

A known solution to this problem is termed "water-filtration", wherein one or two tubes of quartz are typically provided between the lamp and the substrate and distilled deionized water passed through the tubes. This has the effect of filtering out approximately 50% of the infrared radiation.

One problem with this arrangement, however, is that some shortwave ultraviolet radiation is also filtered out, and this may therefore reduce the curing efficiency in some circumstances.

Where only heat-sensitive materials are being irradiated, the reduction in efficiency is an acceptable limitation, but users increasingly desire the flexibility to process a wide range of materials.

Furthermore, in many applications, such heat is only a problem when movement of the substrate commences, stops or when the substrate runs at low speeds.

A possible solution to this problem would be to provide removable water filter tubes or interchangeable reflector heads, but these are expensive and inconvenient and do not resolve the heat problems which occur during starting up and slowing down.

It would therefore be desirable to provide an arrangement which overcomes, or at least mitigates, the above-mentioned problems.

In accordance with a first aspect of the present invention there is provided a lamp assembly comprising a source of ultraviolet and infrared radiation, a directing device for directing a first proportion of the radiation through a filter and a second proportion so as to bypass the filter and a varying device for enabling at least one of the proportions to be varied so as thereby to control the relative amounts of ultraviolet and infrared radiation emerging from the assembly.

In accordance with a second aspect of the present invention there is provided a method of controlling the relative proportions of ultraviolet radiation and infrared radiation incident on a movable substrate in response to the sensed speed of movement of the substrate.

In order that the features and advantages of the present invention will be fully appreciated, preferred embodiments thereof will now be described with reference to the accompanying drawings, wherein:

FIG. 1 illustrates in cross-section a conventional lamp assembly;

FIG. 2 illustrates in cross-section another conventional lamp assembly similar to FIG. 1 but with a single quartz tube;

FIG. 3 illustrates in cross-section a first embodiment of the present invention with moveable reflectors shown in a first positions;

FIG. 4 illustrates in cross-section the first embodiment of the present invention similar to FIG. 3 with the moveable reflectors shown in a second position;

FIG. 5 illustrates in cross-section a second embodiment of the present invention, wherein movable reflectors are operable as a shutter device; and

FIG. 6 illustrates a control system for the shutters.

Examples of conventional lamp assemblies are shown in FIGS. 1 and 2. In these arrangements an elongate ultraviolet lamp 1, which also emits infrared radiation is arranged within an elongate reflective housing 2 which functions as a directing device. One or more quartz tubes 3, through which distilled deionized water is passed, are also provided within the housing 2 such that a large proportion of the radiation from the lamp 1 passes through the water in the quartz tubes 3.

The water serves to filter out a substantial proportion of the infrared radiation which is emitted by the lamp 1.

FIGS. 3 and 4 show a first embodiment of the present invention, which has the same components as those shown in FIGS. 1 and 2 represented by the same reference numerals. In this arrangement, varying devices in the form of two reflector elements 4 are pivotably mounted about respective axes 5. In the positions of these elements shown in FIG. 3, a large proportion of the radiation emitted by the lamp 1 emerges from the lamp assembly without passing through the water filter 3, such that the emergent radiation contains a relatively high proportion of infrared radiation.

In contrast, in the positions of the reflectors 4 shown in FIG. 4, a smaller proportion of the radiation emitted from the lamp 1 emerges unfiltered from the lamp assembly, for two reasons. Firstly, the positions of the reflectors 4 are such that only radiation emitted by the lamp 1 within a narrow angular range can bypass the filter 3. Secondly, the proportion of light reflected by the reflector elements 4 into the filter 3 is greater than in the situation shown in FIG. 3.

In a second embodiment, shown in FIG. 5, the quartz tube 3 is positioned further away from the lamp 1 than in the arrangement shown in FIGS. 3 and 4, and this enables the reflectors 4 to adopt a fully closed state which effectively prevents all of the radiation emitted by the lamp 1 from emerging from the lamp assembly.

In both of the above-described embodiments, the reflectors are moved by means of an electric motor (not shown). The positions of the reflectors 4 are sensed by a position sensor (not shown), and the sensor output is used to control the electric motor in a servo arrangement such that the reflectors 4 are always in the desired position.

The desired position of the reflectors 4 will in practice depend on the nature of the substrate being dried or cured and on the speed at which the substrate moves past the lamp assembly. Thus, in the arrangements described above, as shown in FIG. 6, a speed sensor is advantageously provided which generates an electrical output signal in dependence on the speed of the moving substrate and supplies this to control circuitry for controlling the electric motor. The resulting system will cause the reflectors 4 to adopt the position shown in FIG. 4 or FIG. 5(a) when the substrate is running at a low speed or when starting up or stopping, and, when running at full speed, the reflectors 4 will adopt the position shown in FIG. 3 or FIG. 5(b). Furthermore, when the apparatus is being used to dry or cure a heat-sensitive substrate, the partially closed mode shown in FIG. 4 and FIG. 5(a) would be adopted.

When the system is in an idling situation, the fully shuttered mode shown in FIG. 5(c) is adopted. Although preferred embodiments of the present invention have been described above, it will be clear to persons skilled in the art that a number of alternative arrangements would he possible without departing from the scope of the present invention. For example, although an electric motor is provided in the preferred embodiments for controlling the position of the reflectors, it would be possible to effect such control either manually or pneumatically. Furthermore, although the position of the reflectors is preferably sensed directly, it would be possible to deduce the position by measuring the infrared radiation emitted by the lamp assembly.

Other variations and modifications of the specific embodiments herein shown and described will be apparent to those skilled in the art, all within the intended spirit and scope of the invention. While the invention has been shown and described with respect to particular embodiments thereof, these are for the purpose of illustration rather than limitation. Accordingly, the patent is not to be limited in scope and effect to the specific embodiments herein shown and described nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.