Abstract:
The invention relates to an irradiation device for irradiating objects, comprising a housing having an outlet for the electromagnetic radiation directed at an object to be irradiated and at least one long radiation source for the electromagnetic radiation arranged in the housing. In order to enable bigger irradiation widths in an irradiation device, more particularly in a UV irradiation device, without deformation of the radiation source, at least one of the radiation sources in the irradiation device is rotationally arranged about its longitudinal axis.

Description:
PRIORITY CLAIM 
   This is a U.S. national stage of application No. PCT/EP02/05519, filed on 18 May 2002. Priority is claimed on that application and on the following application: Country: Germany, Application No.: 101 25 770.8, Filed: 26 May 2001. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to an irradiation device for irradiating objects, in particular with ultraviolet and/or infrared and/or visible electromagnetic radiation, comprising a housing which comprises an outlet aperture for electromagnetic radiation, which outlet aperture is aligned to the object to be irradiated, as well as comprising at least one elongated radiation source, arranged in the housing, for electromagnetic radiation. Furthermore, the invention relates to an operating system for a radiation source according to the invention. 
   2. Description of the Related Art 
   Irradiation devices, in particular for UV light, are used for photochemically influencing irradiated objects. Important applications include the curing of printing inks, adhesives and coatings, as well as sterilization and medical irradiation. In particular for applications in the context of wooden board materials and floor coverings, UV irradiation devices with very high radiation outputs are used, with the irradiation width ranging up to several meters. 
   In UV irradiation devices, above all gas discharge lamps are used as radiation sources, in which gas discharge lamps a plasma is generated by the vaporization of metals. The lamps essentially comprise a tubular glass body, two electrodes, two foil fuse-ins as well as two lamp bases. Depending on the lamp type, the operating temperatures at the glass body can reach between 700° C. and 900° C. 
   All known elongated UV irradiation devices comprise a radiation source, suspended at both ends, which radiation source can be partly enveloped by a reflector. 
   The radiation sources are designed such that the energy absorbed by the glass is released by free convection and by radiation. An equilibrium between the absorbed energy quantity and the released energy quantity would occur at a temperature of the glass body of approx. 800° C. However, in practical application, the reflectors and the housing of the UV irradiation device impede this state. Reflection of heat radiation, and at times heat accumulation, can occur near the radiation source. 
   In order to overcome this problem, attempts have been made to set the temperature of the radiation source within the optimal operating range by means of improved air cooling systems. However, such arrangements are associated with a disadvantage that even with optimal cooling of the freely suspended irradiation source, i.e. an irradiation source which is only held by its end, beyond a critical electrical energy level in combination with a critical design length, the temperature of the glass body is such that all known radiation sources suffer deformation as a result of gravitational forces. Such sagging is evident in all irradiation sources, not just in UV radiation sources. Due to creep action in the glass body, whose operating temperature is just slightly below the temperature where material assumes a plastic state, all such radiation sources sooner or later suffer deformation. This particularity is already taken into account when the housing shape and the distance to the object to be irradiated are designed. However, if the deformation becomes excessive, then the plasma arising in the lamp can establish contact with the glass at a point. Such contact causes overheating and consequent destruction of the glass body of the radiation source. 
   In order to reduce deformation it is thus necessary according to the state of the art to reduce the design length of irradiation devices, in particular of UV irradiation devices, and at the same time to reduce the electrical output in the case of longer design lengths. According to the state of the art, large irradiation widths require several irradiation devices to be arranged side by side. 
   SUMMARY OF THE INVENTION 
   It is thus the object of the invention to create an irradiation device, in particular a UV irradiation device which allows larger irradiation widths without there being any deformation of the radiation source. 
   In an radiation device of the type mentioned in the introduction, this object is met in that at least one of the radiation sources in the irradiation device is arranged so as to be rotatable on its longitudinal axis. 
   Rotation of the radiation source on its longitudinal axis evens out the influence which gravitational forces have on creep action in the material of the radiation source. Since, with justifiable expenditure on cooling, operating temperatures can only be reduced to a certain extent, the invention is based on the elimination of the damaging effects of the forces acting upon the radiation source. This is achieved in that as a result of rotation, there is a continuous change in the direction of the gravitational forces which act on the material. 
   In the case of free convection, the temperature at the upper side of the radiation source is higher than the temperature at its lower side, because the upper side is heated up more by the upward-flowing air. As a result of this, the upper side may be subjected to local overheating which can destroy the radiation source. In order to prevent such destruction, radiation sources are designed according to the critical temperature at the upper side. By rotating the lamp, it can be operated at a higher specific output because the region which is exposed to the highest temperatures continuously changes. 
   According to the invention it is possible for several radiation sources to be arranged axially-parallel to each other in one irradiation device, with at least one being arranged so as to be rotatable on its longitudinal axis. Preferably however, all the radiation sources which are arranged in the irradiation device are rotatable. In this case, the radiation sources are advantageously connected to a common drive. The connection can for example be established by way of a belt transmission or a planetary gear arrangement. 
   In order to prevent damage to the body of the radiation source, which body is normally made of glass, the two ends of each rotatable radiation source are accommodated in a rotatably held seat arrangement, with at least one of the two seat arrangements of each radiation source being connected to a drive. If both seat arrangements of a radiation source are connected to a drive, torsion of the body of the radiation source can be substantially prevented as a result of the driving torque. The driving force for rotating the radiation sources can for example be by pneumatic, electric or manual means. However, in the case of short radiation sources, up to approx. 2 m in length, it is sufficient if the drive only engages one end. 
   In particular, in the case of radiation sources which only rotate in one specified direction it is advantageous if the power which is required for their operation is supplied in a contactless arrangement, for example by way of electromagnetic radiation (microwave excitation). As an alternative, a conventional power supply by way of sliding contacts is also possible. 
   If rotation of the radiation sources involves regular changes in direction, the electrical power can also be supplied by way of flexible cables, provided the angles of rotation in both directions are balanced. 
   From DE 199 16 474 A1, an irradiation device comprising an elongated radiation source for irradiating objects with UV radiation is known, whose housing comprises an outlet aperture aligned to the object to be irradiated. For the purpose of heat dissipation, the device comprises a cooling system in which a cooling-gas flow for the forced circulation cooling of the radiation source in the interior of the housing is circulated by fan force and re-cooled by way of a heat exchanger. The fan arrangement is constituted by several radial fans arranged so as to be distributed along the length of the radiation source, with the axes of these fans being aligned perpendicular to the radiation source. The cooling-gas which flows in by way of a lateral channel first flows around the casing of the radiation source and then flows through a longitudinal slit in the crown region of the reflector which is arranged above the radiation source, into a suction chamber which is arranged upstream of the fan. 
   This cooling system is associated with a disadvantage in that several radial fans, distributed along the length of the radiation source, are required for effective cooling. Furthermore, the design height which results from the vertical arrangement of the radial fans can render the use of the irradiation device difficult or even impossible where the available space is restricted. 
   An irradiation device for irradiating objects with electromagnetic radiation according to the invention includes a housing having an outlet aperture for electromagnetic radiation, which outlet aperture is aligned to the object to be irradiated, as well as at least one elongated radiation source, arranged in the housing, for electromagnetic radiation. The irradiation device comprises at least one admission channel and at least one discharge channel for cooling-gas, wherein each channel comprises a cooling-gas aperture which extends in the direction of the elongated radiation source along the length of the radiation source. The radiation source is arranged between the admission channel and the discharge channel, and at least one opposite surface partly envelopes the radiation source by forming a gap which becomes narrower in the direction towards the cooling-gas aperture of the discharge channel. Particularly effective cooling for the elongated radiation source is achieved by separating each channel from the interior space of the housing of the radiation device by means of a flow resistor, in particular a sieve, and by forming one of the channels as an integral part of an elongated barrier which at least partly masks the direct path of the rays from the radiation source to the object to be irradiated. 
   The narrowing gap between the radiation source and the opposite surface increases the flow speed of the cooling-gas from entry to the gap to entry to the discharge channel. This increase in speed prevents the flow from separating from the radiation source and thus ensures that the side of the radiation source which faces away from the admission channel is also always exposed to the flow of cooling-gas. 
   Preferably, when viewed from the outlet aperture for radiation, the discharge channel is arranged in front of the radiation source, while the admission channel is arranged behind the radiation source. Cooling the radiation source provides an additional safeguard against deflection. The cooling-gas, in particular air, which is fed to the discharge channel, preferably at its face, in conjunction with the sieve generates even overpressure along the entire length of the radiation source. The sieve at the discharge channel, which is preferably connected at its face with a negative-pressure generator, evens out the negative pressure along the entire length of the radiation source. 
   Improved cooling of the underside of the radiation source can be achieved in that in particular the discharge channel forms an integral part of the elongated barrier which at least partly masks the direct path of the rays from the irradiation source to the object to be irradiated, wherein each opposite surface for forming the narrowing gap is formed by the surface of the barrier or by reflectors which are arranged between the barrier and the radiation source. The surface of the barrier or of the reflectors partly envelopes the radiation source and forms the gap which becomes narrower in the direction of the cooling-gas aperture. The narrowing gap between the radiation source and the barrier increases the flow speed of the cooling-gas from entry into the gap to entry into the discharge channel. 
   As an alternative, when viewed from the outlet aperture for the radiation, the discharge channel can be arranged behind the radiation source. The reflectors which are arranged behind the radiation source can partly envelope the radiation source as opposite surfaces, thus forming the gap which narrows in the direction of the cooling-gas aperture. 
   In order to generate an equilibrium of forces in the body of the radiation source, rotation of the radiation source can periodically change direction and/or be interrupted. Interruption of rotation combined with a change in rotary direction is advantageous where continuous rotation is undesirable. 
   If the direction of rotation of the radiation source is always changed after partial rotation of the radiation source by at least 180°, then each point of the body of the radiation source experiences the gravitational forces acting upon it, once as a positive and once as a negative force vector, to almost the same extent. Thus any deformation of the radiation source, which deformation occurs during slow rotation, is always reversed again. Advantageous rotational speeds of the radiation source range from 0.1 to 0.2 r/s. 
   In order to keep deformation at an equilibrium, the rotational speed of the radiation source should be kept constant after startup. This ensures that each point of the body of the radiation source is exposed for the same period to the same gravitational forces, both in negative and in positive direction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1   a–c  two diagrammatic front views and a diagrammatic lateral view of a first embodiment of a UV irradiation device according to the invention; 
       FIGS. 2   a, b  two further diagrammatic front views of the UV irradiation device according to  FIG. 1 ; 
       FIG. 2   c  a diagrammatic front view of a second embodiment of a UV irradiation device according to the invention; 
       FIGS. 3   a, b  a diagrammatic view of the operation of the invention, taking into account a cooling-air flow  3 ; and 
       FIGS. 4   a, b  a diagrammatic front view of a third embodiment of a UV irradiation device according to the invention with a particularly effective cooling device. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1   a ) shows a tubular elongated radiation source  1  which is arranged within a housing  2  between a reflector  3  and the object  4  to be irradiated. The path of the rays  5  shown in  FIG. 1   c ) leads to the object  4 , partly directly from the radiation source  1 , and partly indirectly by way of the reflector  3 . The radiation source  1  is arranged in the housing  2  of the irradiation device such that it is rotatable on its longitudinal axis  6 . The ends  7  of the radiation source are held by seat arrangements  8  which are held so as to be rotatable. The driving force for rotating the radiation source  1  is provided by the two drives  9  and the gear arrangement (not shown in detail) arranged therein. The direction of rotation of the radiation source, which direction is indicated by the arrow  11  in  FIGS. 1   a )– c ) can be changed by means of a reversing-control system (not shown) which is known per se. 
     FIGS. 2   a, b  show different operating modes of the irradiation device according to  FIG. 1 . In  FIG. 2   a ) the arrow  12  indicates continuous rotation of the radiation source in a defined direction at a constant rotational speed of 0.1 r/s. In  FIG. 2   b ), the arrow  10  indicates that after partial rotation of the radiation source by at least 180°, the direction of rotation changes each time.  FIG. 2   c ) shows an irradiation device in which a total of 3 radiation sources  1  concurrently rotate on their longitudinal axes  6 , with the arrows  10  indicating that after partial rotation by 180°, the rotational direction of the radiation sources changes each time. 
     FIG. 3   a ) shows an irradiation device comprising an admission channel  13  for cooling-air. Towards the bottom the admission channel  13  comprises an air inlet aperture  15  which extends at least along the length of the radiation source, with the air inlet aperture  15  leading to the interior of the housing  2 . Advantageously, the air inlet aperture  15  is located perpendicularly above the radiation source  1 . The cooling-air flow  14  leaves the air inlet aperture  15  in the direction of the radiation source  1 . If the radiation source  1  is not rotated, the temperature T 1  at the upper side of the radiation source  1  is considerably lower than the temperature at its lower side, where the air flow  15  moves away from the radiation source  1 . In that region the temperature T 2  is considerably higher. This connection is shown in the diagram  16  which shows the increase of the temperature over half the circumference of the radiation source  1  from the lower side to the upper side. 
   If the radiation source  1  is rotated continuously as indicated in  FIG. 3   b ), the temperature differences between the upper side and the lower side of the radiation source  1  are considerably smaller. In the diagram  16  showing the temperature distribution over the circumference of the continuously rotating radiation source, T 1  is the temperature at the upper side, and T 2  is the temperature at the lower side of the radiation source, where the air stream separates. 
   An irradiation device according to  FIG. 4  features effective cooling for both the lower side and the upper side of the radiation source  1 . The radiation source  1 , which in the embodiment shown is a UV lamp, is rotatably arranged in the housing  2 . A screw shaft  17  of the electrical drive  9  intermeshes with a toothed wheel  18  which in a central aperture  19  accommodates one of the ends  7  of the radiation source  1 . 
   The reflector  3  comprises two upper reflector elements  20  which extend along the entire length of the radiation device, and comprises two lower reflector elements  21 . The two upper reflector elements  20  end in the region of an imaginary longitudinal mid-plane through the irradiation device, spaced apart from each other so as to form an air inlet slit  22 . On the upper side of the housing  2  there is an admission channel  13  for the cooling-air. The admission channel  13  extends at least along the entire length of the air inlet slit  22 . At its lower side the admission channel  13  comprises a cooling-air aperture  23  which covers the air inlet slit  22 . A fine-meshed flow sieve  24  is in place between the air inlet slit  22  and the cooling-air aperture  23 . 
   On the rear face of the admission channel  13  there is an inlet  25  by way of which the cooling-air reaches the admission channel  13 . The flow sieve  24  evens out the pressure of the cooling-air along the entire length of the air inlet slit  22 , thus resulting in even cooling of the radiation source along its entire length. 
   In the irradiation device according to  FIG. 4 , the usually occurring separation (explained by means of  FIG. 3 ) between the cooling-air and the radiation source  1  is effectively prevented by means of an additional discharge channel  28 . When viewed from the outlet aperture  29  for radiation, the discharge channel  28  is located in front of the radiation source  1  on the imaginary longitudinal mid-plane through the radiation device. The discharge channel  28  forms an integral part of an elongated barrier, overall designated  30 , with the barrier  30  at least partially masking the direct path of the rays from the radiation source  1  to the object to be irradiated. For this purpose, the barrier comprises reflector elements  31  of curved cross-section, which together form an elongated trough which partly envelopes the radiation source  1  at its lower surface. 
   The reflector elements  31 , which are spaced apart from each other, form an air outlet slit  32  which extends along the entire length of the radiation source  1 . The air outlet slit  32  is separated from a cooling-air aperture  34  of the discharge channel  28  by a further flow sieve  33 . The cooling-air aperture  34  also extends along the entire length of the radiation source  1 . The flow sieve  33  also causes evening out of the pressure relationships at the discharge channel  28 ; however in this case it is related to the negative pressure present in the discharge channel  28 . The negative pressure is for example generated by a vacuum pump (not shown) which is connected on the rear face at an outlet  35  of the discharge channel  28 . This negative pressure can however also be generated by a fan arrangement whose suction side is connected to the discharge channel, and whose positive pressure side is connected to the admission channel. In the circuit which is closed in this way, cooling-air is additionally filtered and re-cooled. 
     FIG. 4  shows that the reflector elements  31 , which form the surface of the barrier, form a gap  36  which narrows in the direction of the discharge channel  28 . Consequently, the cooling-gas flow  14  which enters the gap  36  on both sides of the radiation source  1  is accelerated, and in this way separation of the cooling-gas flow  14  from the radiation source  1  at the lower side of the radiation source  1  is effectively prevented. Despite such effective cooling of the lower side of the radiation source  1  by means of the discharge channel  28  which is integrated in the barrier, due to heat absorption of the cooling-air flow, the temperature at the lower side of the radiation source  1  is still higher. Although this temperature difference is clearly less pronounced than is the case in an irradiation device according to  FIG. 3   a,  for further evening out of the temperatures it is expedient if the radiation source is arranged so as to be rotatable, and if the radiation source is rotated during operation, as shown in  FIG. 4   a ). 
   The cooling device described can however also be used to advantage in radiation devices with statically arranged radiation sources, as shown in  FIG. 4   b ).