Abstract:
A device for tensioning the corona-discharge wires of e.g. electrostatic copiers has an internally toothed sleeve member in which an externally toothed clamping member is turnably received. Both members have openings transverse to the longitudinal axis of the sleeve member. When an end portion of a corona wire whose other end is fixedly secured, is inserted through both openings in aligned condition of the same, turning of the clamping member draws the end portion between the members, tensioning the wire and clamping the end portion between the teeth of the members.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wire-tensioning device. 
     More particularly, the invention relates to a device for tensioning corona-discharge wires. 
     Still more specifically, the invention relates to a device for tensioning corona-discharge wires such as are used in electrostatic copiers. 
     2. The Prior Art 
     For reasons known to those skilled in the art it is necessary for corona-discharge wires to be taut, i.e. not to have any slack. This is true particularly, although not exclusively, in electrostatic copying machines. 
     Devices for this purpose are already known, for example from German allowed application No. 2,641,396. In the device disclosed therein the free end of a corona wire (the other end is secured in suitable manner so as to be fixed) is engaged and the wire at the same time tensioned by means of a wedge which is inserted transversely to the elongation of the wire into a slightly conical opening. However, such an arrangement can transmit only a relatively limited tension to the wire since tensile forces acting in the longitudinal (i.e. tensioning) direction of the wire can in effect occur only at that edge at which the wire end portion entering beneath the wedge is first engaged and clamped by the wedge. This is understandable because, if it were not the first wire end engaged by the wedge which is clamped without freedom of escaping movement, then the tensioned wire would be capable of lifting the wedge out of its seat. There is, therefore, only a single clamping edge or point in this arrangement, and this in turn means that where the material is engaged at this single point the material of the wire can begin to flow under the very strong stresses acting upon it at this point, with the result that the originally achieved degree of tensioning deteriorates over a period of time, and sometimes deteriorates very rapidly. 
     SUMMARY OF THE INVENTION 
     It is, accordingly, an object of the present invention to provide an improved corona-discharge wire tensioning device which avoids disadvantages encountered in the prior art. 
     More particularly, it is an object of the present invention to provide such an improved corona-discharge wire tensioning device which makes it possible to tension the discharge wire to any desired degree without permitting slackening of the tension due to flowing of the wire material or to other causes. 
     Pursuant to these objects, and others which will become apparent hereafter, one aspect of the invention resides in a device for tensioning corona-discharge wires which are fixedly secured at one end, particularly for use in electrostatic copiers. Briefly stated, such a device may comprise an internally toothed sleeve member and an externally toothed clamping member which is received within the sleeve member. Each of these members has a transverse opening inclined to the longitudinal axis of the sleeve member so that, when a free end portion of a corona-discharge wire is inserted through both of the openings when the same are in registry and the members are thereupon turned relative to one another, the free end portion of the wire will be drawn and become clamped between the teeth of the members under simultaneous tensioning of the wire. 
     It will be appreciated that with this arrangement it is possible, by turning of the clamping member, to impart to the wire a tensioning movement--and therefore a degree of tensioning--which can be selected at will. The free wire end inserted into the registering openings will, when relative turning of the sleeve member and clamping member is effected, become wound about the clamping member and thus drawn into the device. After a relatively small angular displacement of the two members relative to one another (usually of the clamping member to the sleeve member) the wire will already be clamped at a plurality of edges constituted by the internal and external teeth of the members. The tension acting in the wire is transmitted from tooth to tooth and, due to the tendency to turn the clamping member backwards counter to the arresting action of the teeth, the clamping effect at the individual edges engaging the wire is even further increased. Since the fire wire end is drawn into the device it will be appreciated that double the number of effective clamping edges is available until this free wire end is totally received in the device. In addition, this drawing-in of the free wire end has the further advantage that any danger of an unintended contacting of the free wire end with conductive or current-conducting components becomes the smaller, the more the wire is tensioned and, consequently, the more the free end portion of the wire is drawn into the device. 
     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 drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a section through a device embodying the invention, taken on line I--I of FIG. 2; and 
     FIG. 2 is a section taken on line II--II of FIG. 1. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     An examplary embodiment of the device according to the present invention is illustrated in FIGS. 1 and 2 which show different sections. The device includes a profiled member 1 of metallic material, for example aluminum, which is of essentially U-shaped configuration and serves as the corona housing. Inserted into the housing 1 is an insulating member or support 2 which is constituted of an electrically insulating synthetic plastic material, for example the polycarbonate which is commercially available under the tradename &#34;Makrolin&#34;. The lower part of the housing 1 has L-shaped guide rails 1a which can be inserted into a holding member for the housing 1, in known manner. The holding member and, in fact, details of an electrostatic copier with which the device according to the invention can be used, are not illustrated because they do not form a part of the present invention. The purpose of providing the rails, however, is so that the device can be readily inserted into and withdrawn from the holding member which in turn is a part of a larger device, for example an electrostatic copier, so that the device according to the present invention--and in fact the entire corona discharge device--can be readily removed for inspection and cleaning. 
     The drawing shows that the member 2 is connected with the member 1 by means of portions 2a which are upset in rivet-like manner in openings of the member 1. The member 2 is further provided with a handle 2b formed with serrations or the like but extends from the end of the member 1 and which can be engaged to facilitate the withdrawal of the member 1 and its associated components. The serration facilitates gripping. The member 2 is further provided with an opening 2c into which a metallic sleeve 3 is inserted. The inner circumferential surface of the sleeve 3 is provided with an annulus of teeth 3a which in the illustrated embodiment are of sawtooth-shaped cross-section but need not have this particular cross-section. Member 3 is provided with a contact pin 3b which may but need not be of one piece with it and onto which a slotted socket 4 can be pushed which serves to supply electrical energy for the corona wire. The upper edge of the sleeve 3 is provided with a transversely extending slot 3c into which a corona wire 5 to be tensioned can be placed. 
     Received within the sleeve 3 is a clamping member 6 which is here of generally cylindrical configuration and provided with an outer annulus of teeth 6a; again, the teeth 6a are of sawtooth-shaped cross-section but could have a different cross-section. The member 6 is of an electrically insulating synthetic plastic material, preferably of a polycarbonate such as the commercially available product called &#34;Makrolin&#34; mentioned above and of which the member 2 may also be made. The upper end portion of the member 6 is provided with a head 6b formed with a slot 6c into which a screwdriver or analogous bladed tool may be inserted which serves to turn the member 6 within the sleeve 3. Intermediate the head 6b and the portion provided with the teeth 6a the member 6 is formed with a circumferential recess 6d, i.e. the teeth 6a have their uppermost ends located at some distance from the head 6b. 
     As FIGS. 1 and 2 both show, that axially extending portion of the member 6 which is provided at the exterior with the teeth 6a is formed with a slot 6e which subdivides it into two halves and extends upwardly to the region of the recess 6d. The purpose of this is to allow the member 6 over its entire axial portion which is provided with the teeth 6a, an elastic &#34;springy&#34; movement in radial direction. This means that when the member 6 is turned in the direction of the arrow A (see FIG. 2) the sawtooth-shaped teeth 6a of the member 6 can snap behind the sawtooth-shaped teeth 3a of the member 3. This makes it possible to very readily turn the member 6 relative to the member 3 by a distance corresponding to one tooth at a time, and the cooperating teeth 3a and 6a prevent a reverse turning of the member 6 (i.e. counter to the direction of the arrow A) under the tension of the corona wire 5 which is being stretched. The springy arrangement of the member 6 permits it, or rather permits the two halves of the member 6, to yield sufficiently in inward direction so that one or more convolutions of the wire 5 can become accommodated between the teeth 3a and 6a; this is clearly visible in FIG. 2. 
     When a corona wire 5 is to be tensioned the same is so placed into the slots 3c of the sleeve 3 and a slot 2d formed in the member 2, that a small free end portion 5a of the wire extends out from and beyond the sleeve 3. The member 6 is then so inserted into the sleeve 3 that the slot 6e of the member 6 is aligned with the slots 2d of member 2 and 3c of member 3. Subsequent turning of the member 6 in the direction of the arrow A, e.g. by means of a tool inserted into the slot 6c, causes the corona wire 5 to be tensioned in that it is pulled into the sleeve (in leftward direction in FIG. 2) whereas at the same time the projecting free end portion 5a is also pulled into the sleeve 3 (rightwards in FIG. 2). The portions of the wire which are thus drawn between the teeth 3a and 6a become clamped between them and are engaged by a number of teeth which is the greater the more of the wire is drawn into the sleeve. 
     When the wire 5 has been tensioned to the requisite degree an electrically insulating cover 7 (which may again be of the trademarked material &#34;Makrolin&#34; or another electrically insulating synthetic plastic material) is then placed onto the device so as to protect the device against engagement by a user or operator to eliminate the danger of injury from shock; this is particularly important if a part of the free end portion 5a is still located outside the sleeve 3. A projection 7a of the cover 7 engages and holds stern the wire 5 when the cover 7 is put in place, thus preventing the wire 5 from slipping, e.g. axially (see FIG. 1) of the member 6 out of the space between the teeth 3a and 6a. 
     Of course, the teeth 3a and 6a need not be of sawtooth-shaped cross-section. However, if they do have this cross-section this is particularly advantageous because it offers an especially high degree of resistance to reverse turning (counter to the arrow A) of the member 6 under the tension exerted upon it by the tensioned wire 5. It is also possible for the sleeve to be radially yieldable, instead of the member 6, and it will be appreciated that instead of the slot 6c for insertion of a blade 2 some other configuration could be chosen, for example a head 6b which would extend farther upwardly than illustrated in FIG. 1 and which would be of e.g. hexagonal outline for engagement with a wedge. Combinations of materials different from those which have been described above are conceivable. It has been found, however, that a particularly good tensioning effect with very low tendency for slackening over prolonged periods of time is achieved if it is the member 6 which is made of synthetic plastic material and if the sleeve 3 is of metallic material. The members 3 and 6 need of course not be mounted on the member 2 in the particular manner illustrated, nor need the member 2 be connected with the member 1 in the specific illustrated way. The use of the cover 7 is also optional, but highly advantageous because it provides an added safety factor all by itself, and the provision of the holding-down projection 7a for the wire 5 adds to this a further margin of safety against undesired touching of the wire 5 by a user or operator. 
     While the invention has been illustrated and described as embodied in a device for tensioning corona-discharge wires, 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.