A FILM EXAMINING CABINET

Abstract: A film examining cabinet has a light surface (2) for transilluminating transparent film. The cabinet light sources are comprised of so-called compact fluorescent tubes (3) having a tube base and an electrical connector solely at one end of the tube. Two mutually parallel tube sections (3b) extend from the tube base and are mutually joined by a curved tube section. The compact fluorescent tubes are placed vertically in the cabinet with the tube bases accommodated in a channel or accommodating part (1a) positioned above and/or beneath the light surface (2) or above and/or beneath light fields belonging to said surface. The effective length of the fluorescent tube sections (3b) corresponds to the full height of the light surface (2) or to half the height of the light surface.

Description: A FILM EXAMINING CABINET FIELD OF INVENTION The present invention relates to a film examining cabinet of the kind defined in the preamble of Claim 1. In order to fulfil commercial standard requirements relating to film examining cabinets for transilluminating transparent film, the smoothness of the light surface and the light intensity must not deviate from preset values. The size of the light surface is determined by standard X-ray film formats. A normal requirement is that four films measuring 35 x 43 cm can be hung in juxtaposed relationship in one or two rows, wherein the width or height of the light surface is about 1.5 x 0.5 or 1.5 x 1 m. The light surface is normally divided into fields having widths of 0.375 m, and a permanent light cabinet is manufactured in sizes capable of accommodating one, two, three or four such fields. Film examining cabinets that are provided with motorized devices for rational examination of films most often have a light surface in the region of 1.5 x 1 m, this surface being divided into two light fields measuring 1.5 x 0.5 m, or in 2 x 4 light fields measuring 0.375 x 0.5 m. The lighting source used is normally comprised of fluorescent tubes. These tubes are of a standard size, so as to achieve compatibility between existing cabinets. In the case of film examining cabinets of the kind to which this document refers, the fluorescent tubes used have been found to have the common drawback whereby the intensity of the light emitted at the electrode carrying ends is much weaker than the light emitted along the remainder of the tube. It has been necessary to fulfil the standard retail requirements of the light surface by adapting the size of the light cabinet to the current film format and size of fluorescent tube. Even though existing types of fluorescent tubes more or less coincide well with film format and light surfaces, the need to fulfil the retail requirement of light uniformity often presents a problem because of the limited built-in measurements of light cabinets and fluorescent tubes, and not least because of the weaker light at the ends of the fluorescent tubes. It shall be noted in this regard that the light surface shall possess light spreading properties which will prevent recording of the shape or outlines of the light source, which would make diagnosis more difficult. Although a deeper light cabinet will improve the light spreading effect, the light intensity will be decreased at the same time. A light cabinet must not be made too deep for other reasons, since permanently fixed and wall-mounted cabinets would then become too clumsy and bulky and make instal¬ lation of motorized film examining equipment difficult to achieve. In order to fulfil the requirement relating to light quality in light cabinets of acceptable depth, it has hitherto been neces¬ sary to provide light cabinets with a relatively large number of fluorescent tubes. The problem presented by weak light at the ends of the fluorescent tubes still remains, however. Attempts to achieve light uniformity by mixing fluorescent tubes of different powers and different light intensities have resulted in unaccept¬ able variations in colour temperature. Furthermore, the problem concerning the central control of light darkening becomes complicated when using a mixture of different types of fluores¬ cent tubes, resulting in much poorer light uniformity at maximum light intensities and at lower light levels. OBJECTS OF THE INVENTION One object of the present invention is to provide a film examin¬ ing cabinet of the aforedescribed kind with which the aforesaid drawbacks are avoided and which enables the manufacture of light cabinets that can be readily adapted to prevailing requirements with small modifications regarding the size of the light surface and field division in correspondence with existing film dimen¬ sions. Another object is to provide a film examining cabinet that enables light quality to be improved as a result of extremely effective spreading of light and light uniformity. SUMMARY OF THE INVENTION These and other objects are fulfilled with a film examining cabinet of the aforedescribed kind that has the characteristic features set forth in the characterizing clause of Claim 1. The use of a so-called compact fluorescent tube that has an electrical connector and an electrode solely in that end of the tube to which the tube base is fitted, and by choosing a tube length that is greater than the height of the light opening, solely the effective light length of the tube will be used. This completely eliminates the problem of weak light at the ends of the fluorescent tubes. The vertical positioning of the compact fluorescent tubes - which may have the present standard length of 542 mm - enables the mutual positioning of the tubes to be readily varied, with different numbers of tubes and different spacings therebetween to suit the selectivity desired with regard to the field division of the light surface. In this regard, luminescent tubes can be disposed in an upper field relative to the light surface with the tube bases facing upwards in an overlying channel part or accommodating part of the cabinet, and fluorescent tubes can be disposed in a lower field with the tube bases facing downwards and accommodated in a corresponding channel or accommodating part downwardly of the light surface. The upper and lower fields are conveniently delimited from one another by means of a centrally positioned and horizontally extending cabinet partition wall. Alternatively, the tube bases may be accommodated in a central accommodating part of the cabinet and faced upwards and downwards from said accommodating part so as to illuminate different fields in the light surface. The upper and lower fields may also be divided into smaller fields, e.g. four smaller fields, in which the fluorescent tubes are disposed so as to obtain the greatest spread of light. In this regard, it is preferred in practice to position the fluorescent tubes in the region of the rear wall opposite the cabinet light surface, such that parts of a fluorescent tube will be located at different respective distances from the light surface. It has been established that the light is spread more effectively in this case than when the parts of the fluorescent tubes lie in a plane that is parallel with the light surface. Light is spread very effectively when the parallel tubular parts of the fluorescent tubes are placed in the cabinet so as to lie perpendicularly to a vertical plane to the light surface. The fact that the forwardly lying part of a fluorescent tube will then "obscure" a rearwardly lying part has not been found disadvantageous in practice. On the contrary, the light emitted by the fluorescent tubes is found to spread more uniformly. Trials have shown that when the fluorescent tubes are positioned such that both sections of respective fluorescent tubes lie in a plane parallel with the light surface, the concentration of light is so powerful as to make it impossible to achieve an equally uniform spreading of the light without greatly increasing the number of fluorescent tubes used. In the case of an inventive film examining cabinet, it is preferred that the fluorescent tube drive devices or starters (chokes) are supported externally of the cabinet, preferably on the rear side thereof. This avoids the starters or high frequency devices from deleteriously influencing the spread of light in the cabinet. In this regard, the drive devices may be carried by a plate which is mounted in the cabinet and has a part that projects through apertures provided in the rear wall of the cabinet to this end. This arrangement enables the drive devices to be easily reached for exchange or repair from the front side of the cabinet, for instance when replacing fluorescent tubes. Thus, the fluorescent tubes are removed first, before detaching the plate carrying said drive devices from the rear wall of the cabinet. One reactor or drive device is normally used for two compact fluorescent tubes of the aforesaid kind. Further features of the invention will be evident from the following depending Claims. Some of the advantages afforded by the invention are governed by the fact that certain film formats must be used with film examining cabinets of the aforesaid kind, this film format governing, in turn, the format of the light surfaces. This applies to both two field cabinets and eight field cabinets. Since the compact fluorescent tubes used have certain standard lengths, it is not possible to choose freely fluorescent tubes and light surfaces that will provide an optimal spreading of the light emitted. However, the present invention enables the use of existing compact fluorescent tubes of suitable standard lengths that correspond to the size of the light surface concerned, wherein any excessive length of the tubes can be accommodated in the channel part or accommodating part of the cabinet together with the tube bases. Thus, only the effective light length of the tubes will be used, more specifically in a manner which spreading of the light will fulfil the current requirements of the authori¬ ties and of commerce. The present invention also enables the same positioning of the fluorescent tubes to be used, but with the number and mutual spacing between said tubes to be varied in different cabinet models. For instance, six fluorescent tubes may be used in a film examining cabinet that has one light field. When this light field is to be divided into four smaller fields in another examining cabinet, this can readily be achieved by using a further two fluorescent tubes and altering the mutual spacing of the tubes. In this latter case, each smaller field will be illuminated by two fluorescent tubes, which are conveniently placed relatively close to the side walls of respective fields. Additional fluorescent tubes can be fitted readily to the cabinet, when wishing to increase the number of fields. The invention will be described below in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially cut-away perspective view of an inventive film examining cabinet provided with two light fields. Fig. 2 is a corresponding view of a similar film examining cabinet whose light surface presents eight light fields. Fig. 3 is a cross-sectional view of the film examining cabinet shown in Fig. 1. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Shown in the Figures is a film examining cabinet 1 having a light surface 2 for illuminating transparent film (not shown) mounted in front of the light surface. The light surface may have a typical size of 1.5 x 1 m, and the depth of the cabinet may be between 120 and 200 mm, typically 150 mm. The cabinet 1 shown in Fig. 1 has a horizontal partition wall lb that divides the light surface 2 into an upper and a lower field. The cabinet 1 shown in Fig. 2 also includes three vertical walls lc which function to divide the upper and the lower light surface into four smaller fields, i.e. to provide a total of eight fields. Each of these fields has a width of 0.375 m, and the fields enable eight X-ray films each measuring 35 x 43 cm to be hung for examination. Each of the two fields in the cabinet shown in Fig. 1 is illumi¬ nated by six fluorescent tubes 3. These tubes are so-called compact fluorescent tubes with the tube base 3a and electrical connector located solely in one end of the tube, wherein two tube sections 3b extend from the base parallel with one another and are mutually joined by a bend at their base distal ends. The effective light-emitting length of the tube sections 3b corresponds to half the height of the light surface 2. The fluorescent tubes 3 are positioned vertically with the tube bases 3a in the upper field accommodated in a channel or accommo¬ dating part la of the cabinet 1, above the light surface 2. Correspondingly, the fluorescent tubes 3 belonging to the lower field are accommodated in a corresponding channel or accommodat- ing part la located beneath the light surface. The fluorescent tubes 3 thus extend upwards and downwards from said accommodating parts, almost to the horizontal partition wall lb of the cabinet. The fluorescent tubes are placed in the proximity of the rear wall Id of the cabinet, which lies opposite to the light surface. More specifically, the fluorescent tubes are positioned so that the mutually parallel tube sections 3b lie in a vertical plane that lies perpendicular to the light surface 2. As before mentioned, this positioning of the tubes spreads the light emitted by said tubes more effectively. As will be seen from the cross-sectional view shown in Fig. 3, the drive devices or starters (chokes) belonging to respective fluorescent tubes 3 are mounted externally of the cabinet 1, more specifically on the rear side of the cabinet. In the illustrated case, the drive devices 5 are carried by a plate 6 which is secured to the rear cabinet wall Id inside the cabinet 1 with the aid of screws 7, wherein the wall includes a part 6a which protrudes through an aperture provided in the rear cabinet wall Id. This enables the drive devices to be removed quite easily, by first removing the fluorescent tubes 3 and then loosening the plate 6 from the rear wall. In the Fig. 2 embodiment, which includes eight light fields, each field is provided with two compact fluorescent tubes 3, each fluorescent tube being placed adjacent a cabinet side wall lc that delimits the different fields. The cabinet illustrated in Fig. 2 thus accommodates sixteen compact luminescent tubes, i.e. four more than the cabinet shown in Fig. 1. A tube base accommodating part la may also be provided in the centre part of the cabinet, said luminescent tubes extending upwardly and downwardly from their respective tube bases. The horizontal wall that extends in front of the tube bases and covers said bases so that only the effective length of the luminescent tube is covered by the wall may also contribute to dividing the light surface into respective fields. The effective length of respective fluorescent tubes may, also in this case, correspond to the full height or to half the height of the light surface above or beneath the centre wall. The number of fluorescent tubes used may readily be varied to correspond to the number of fields in the manufacture of the cabinet, since the tubes can be readily fitted and secured in desired places in the upper, lower and central accommodating channel la respectively. The best light spreading effect is obtained when the walls are painted a dull white colour or a light gray colour.

Claims: CLAIMS 1. A film examining cabinet that includes a light surface (2) for transilluminating transparent film placed in front of said surface, wherein the cabinet (1) accommodates a plurality of light sources in the form of fluorescent tubes (3), characterized in that a) the fluorescent tubes are compact fluorescent tubes (3) comprising a tube base (3a) and an electrical connector at solely one end of the tube, and further comprising at least two mutually parallel tube sections (3b) that extend from the tube base and are mutually joined by a curved section distal from said base; b) the effective light-emitting length of the luminescent tube sections (3b) corresponds to the whole height or half the height of the light surface (2); c) the fluorescent tubes (3) are positioned vertically; and d) the tube bases (3a) are accommodated in a channel part or accommodating part (la) of the cabinet (1) located above and/or beneath the light surface. 2. A cabinet according to Claim 1, characterized in that the fluorescent tubes (3) are placed in the proximity of the rear cabinet wall (Id) opposite the light surface (2) of said cabinet, such that the tube sections (3b) of a fluorescent tube (3) are spaced at mutually different distances from the light surface. 3. A cabinet according to Claim 2, characterized in that the parallel tube sections (3b) of respective fluorescent tubes (3) are positioned in the cabinet (1) so that said sections lie in a vertical plane that extends perpendicularly to the light surface (2). 4. A cabinet according to any one of Claims 1-3, characterized in that the fluorescent tube drive devices or starters (5) are mounted externally of the cabinet (1), preferably on the rear side thereof. 5. A cabinet according to Claim 4, characterized in that the drive devices (5) are supported by a plate (6) fitted in the cabinet and having a part (6a) that projects through a hole or aperture provided in the rear wall (Id) of the cabinet. 6. A cabinet according to any one of the preceding Claims, wherein the light surface is divided into different fields by at least one horizontal partition wall (lb) and several vertical partition walls ( lc) , characterized in that each field accommo¬ dates two fluorescent tubes that are placed adjacent vertical side walls delimiting respective fields. 7. A cabinet according to any one of the preceding Claims, characterized in that the light surface measures about 1.5 x 0.5 or 1.5 x 1 m.

Inventors: OHLSON CARL-ERIC, OHLSON, CARL-ERIC
Applicants: AO MEDICAL PRODUCTS AB
Application year: 1997
Main classification: G02B27
IPC codes: G02B27, G09F13