Patent Publication Number: US-3971912-A

Title: Fixing arrangement for fusing tower images

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to fixing arrangements for fusing the toner of toner images by means of heating wires stretched between holding rails and extending in the direction of the transport path of the toner images. 
     With known fixing arrangements of this type, a plurality of discrete heating elements, such as metal strips, are each separately secured in a clamping arrangement by means of tightening screws. As a result, the assembly of such a fixing arrangement, and in particular the securing in position of the heating elements, is relatively time-consuming and accordingly involves a considerable labor cost. 
     SUMMARY OF THE INVENTION 
     It is a general object of the invention to provide a fixing arrangement in which the assembly of the heating element is simpler and accordingly involves a lower labor cost than in the prior art. 
     This object, and others which will become apparent from the description, below, of a preferred embodiment, can be met, according to one advantageous concept of the invention, if the plurality of heating wires are formed as parts of a single heating winding, and if ceramic holding bodies provided with holding portions each serving to hold at least one turn of the heating coil are strung onto holding rails. Preferably, on the ceramic bodies the holding portions for the turns of the heating winding are provided in the form of holding hooks which define holding openings which are open at the free ends of the respective hooks for receipt of a turn of the heating winding, but which are closed off when after the insertion of the respective turn of the winding the next such ceramic body is strung onto the respective one of the holding rails. 
     In this way, there is achieved the advantage that the securing of the resistive heating wire requires merely the hooking of successive turns of the wire onto the holding hooks of successive ones of the ceramic bodies. After all the ceramic bodies have been slid onto the respective rails, the holding portions of the ceramic bodies are so spaced relative to the respective adjoining ceramic bodies as to preclude an exit of the turn of the winding from the opening formed between the respective holding portion and the remainder of the respective ceramic body. 
     A particularly simple and stable design for the inventive fixing arrangement results by providing two end plates arranged parallel to each other and to the transport direction of the toner image and by securing to these plates the opposite ends of a slide rail oriented transverse to such transport direction, and providing a further slide rail whose opposite ends are likewise secured to the end plates and which is likewise oriented transverse to the toner image transport direction, but with this latter slide rail being mounted on pivotable arms which are spring-biased in a direction tending to maintain constant the stressing of the resistive heating wire. 
     The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a side view of an embodiment of the invention, as viewed in the direction of the arrows I--I in FIG. 2; and 
     FIG. 2 is a sectional end view of the embodiment of FIG. 1, the section being taken along the line II--II in FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The fixing arrangement shown in FIGS. 1 and 2 includes two parallel end plates 2 and 3 oriented parallel to each other and to the transport direction A of a copy carrier bearing a powder image to be fixed. A rail 10 oriented transverse to the toner-image transport direction is connected to the end plates 2 and 3. In particular, the opposite ends of the rail 10 are secured to respective ones of bent tab portions 2c, 3c on the end plates 2, 3. A pivot shaft 4 connects together the right-hand ends of the plates 2, 3, passing through holding apertures in the plates. The end portions 4a, 4b of the pivot shaft 4 project past the holding apertures and serve to mount pivotable arms 5. The pivotable arms 5 and the pivot shaft 4 are held in place, in direction longitudinally of the shaft 4, by means of circlips 7 engaging the shaft 4, at the ends 4a, 4b thereof. The pivotable arms 5 have bent-over tab portions 5a to which are connected by means of screws 11, 12 respective ones of the opposite ends of a further rail 9 likewise oriented transverse to the toner-image transports direction A. 
     The upper pivotable arm 5 is provided with a projection 51 having a holding notch 5d. Likewise, the end plate 2 is provided with a projection 2e having a holding notch 2d. A tension spring 25 extends between the projections 2e, 51, its ends being received in and held by the holding notches 2d, 5d. The biasing force of tension spring 25 urges the pivotable arm 5 to turn in clockwise direction, as viewed in FIG. 2. Accordingly, the rail 9 is urged to move in the general direction of arrow B. As a result, the heating winding, which is stretched between the rails 9 and 10 in a manner described in detail below, assumes a stressed condition substantially independent of the temperature of the heating winding. In this way, loosening and drooping down of the heating winding when it is hot, so that it comes into contact with a toner-image-bearing copy carrier travelling in a plane parallel to the picture plane of FIG. 1, is prevented. 
     A plurality of ceramic holding bodies 15 are successively slid onto each of the rails 9, 10. Each ceramic holding body 15 is provided with an integral holding hook 15a which defines with the remainder of the respective ceramic body 15 a holding opening 15b which is open at the free end of the respective holding hook 15a. Each turn of a strip-shaped heating winding 16 is inserted into the holding opening 15b and passed around the holding hook 15a of a respective one of the ceramic bodies 15. After a turn of the heating 16 is inserted into one of the holding openings 15b and passed around the respective holding hook 15a, the next (in FIG. 1, the next lower) ceramic body 15 is slid onto the rail 9 or 10. The surface of such next ceramic body 15 which adjoins the opening intermediate the holding hook 15a and the remainder of the previously slid-on ceramic body 15 in effect closes off such opening, thereby preventing removal or exit of the accommodated turn of the winding. 
     To assemble the heating winding 16, one starts with a winding 16 having approximately the bent configuration shown. One then hooks the holding hook 15a of one of the ceramic bodies 15 into one turn of the winding 16, and then slides such ceramic body 15 onto the slide rail 9 or 10, preferably alternating between the rails 9 and 10. After all the ceramic bodies 15 have been slid onto the rails 9 and 10, the rails 9 and 10 are secured by means of the screws 11-14 to the end plates 2, 3 or to the pivotable arms 5. 
     When the rails 9, 10 are screwed to the end plates 2, 3 and to the pivotable arms 5, the respective bent tab portions 2c, 3c, 5a of the end plates 2, 3 and pivotable arms 5, which abut against the four end ones of the ceramic bodies 15, prevent separation of the ceramic bodies 15 from each other, and accordingly prevent undesired freeing of the hooked turns of the winding 16. 
     Finally, the ends 16a, 16b of the winding 16 are electrically connected to metal claps 19, 22 clipped onto the end ones of the ceramic bodies 15 on the rail 10. Electrical leads 20, 21 and 23, 24 are connected to respective ones of the two metal clasps 19 and 22. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
     While the invention has been illustrated and described as embodied in a toner-image-fixing arrangement making use of only a single heating winding 16, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.