Feeder for a printer
FIELD OF THE INVENTION 
     The invention relates to a feeder for a printer, particularly a dot matrix printer. The feeder is provided with a pair of tractors for guiding and/or advancing the record carrier, and hinged parts of the tractor are fastened pivotally. 
     BACKGROUND OF THE INVENTION 
     Feeders for printers accomplish the line-by-line, step-by-step, or continuous advance of the record carriers (which consist, e.g., of paper webs). For a trouble-free operation of a printer, it is important that the beginning of the paper web be put expertly in the advance or guide elements of the feeder. 
     When putting the paper web on the pins of the belt fastener of a tractor, it is necessary, for example, to swing away the tractor flaps (i.e., covers) which hold the paper web on the pins. Therefore, tractor flaps are held movably in pivoting bearings. 
     Introduction of the paper web from the underside or backside of the printer also makes the swinging out of hinged parts by means of pivoting bearings necessary in some printer designs. 
     For shipping, swinging in of the hinged elements, which are swung out during operation, is advantageous to save shipping and packing space. 
     All of the examples given above have the disadvantage that hinged parts on printers require a considerable expenditure for pivoting bearings. An additional expenditure arises if the hinged part must further be fixed in the positions to which it is pivotable. An expenditure in this connection is hardly economically justifiable. 
     OBJECTS OF THE INVENTION 
     Therefore, the principle object of the invention is to provide a simple pivoting bearing for hinged parts on the printers. 
     A further object of the invention is to provide a simple fastener for the hinged positions. 
     SUMMARY OF THE INVENTION 
     The objects of the invention are obtained by the provision of a spring steel wire piece cut to length. The spring steel wire piece is put under tension by bending, and it serves as a pivot pin. Additionally, the spring steel wire piece fixes the hinged parts in closed or open position. 
     This invention provides the necessary pivoting joint in an economical and simple way. Additionally, it allows fastening of the hinged part in the desired end positions. 
     A preferred embodiment of the invention is designed so that the tractor bearings in which the ends of the spring steel wire piece is mounted are provided on the tractor body separated in the advance direction. Further, a hinged part bearing with a through-hole for the spring steel wire piece is provided on the hinged part between the tractor bearings of the tractor body. In the closed and open end positions, the hinged part bearing or bearings adjoin outside, planar surfaces on a planar counter surface of the tractor body. The axes of the bores in the tractor bearings and the axis of the hinged part bearing are parallel to but spaced from one another. 
     A functionally inverse design consists in that hinged part end bearings, in which the ends of the spring steel wire pieces are mounted, are provided on the hinged parts separated in the advance direction. Further, a tractor bearing with a through-hole for the spring steel wire piece is provided on the tractor body between the hinged part end bearings. In the closed and open end positions, the hinged part end bearings adjoin outside, planar surfaces on a planar counter surface of the tractor body. The axes of the through-holes in the tractor bearings and the axes of the hinged part end bearings are parallel to but spaced from one another. 
     The spring steel wire piece can be prevented from falling out by the ends of the spring steel wire piece being pinched. 
     The effects according to the invention occur with the hinged parts for printers when the parallel axes of the bores in the tractor bearings and in the hinged part bearings are at a distance of about 0.8 mm. 
     The practical fixing positions are advantageously achieved by the outside planar counter surface of the tractor body and the planar surfaces of the hinged part bearings for the closed and open positions being at approximately 90° to another. 
     Application of the invention to a dot matrix printer occurs by the hinged part consisting of a cover flap for the belt fastener of the tractor. 
     Another applicability is obtained by the hinged part consisting of a side guide flap for the record carrier. 
    
    
     Embodiments of the invention are shown in the drawings and are described in detail below. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the top part of a tractor of a dot matrix printer. 
     FIG. 2 is a view of the right part of a feeder, including a tractor and an additional guide for the record carrier, seen approximately in the feed direction of the record carrier. 
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     The tractor according of FIG. 1 is shown without the record carrier. However, the tractor shown is placed in a pair on the left and right of the record carrier. A left tractor 1a can be seen in FIG. 1, and a right tractor 1b can be seen in FIG. 2. In use, the two tractors 1a and 1b are carried on a fastening rod 2 and a drive shaft 3. The fastening rod 2 and the drive shaft 3 are adjusted to be exactly parallel by side supports 4 and set screws 5. The fastening rod 2 runs through a bore 2a, and the drive shaft 3, which is square in cross section, runs through a square bushing which is inserted into a bore 3a. In this case, the drive shaft 3 is rotatably mounted in a bushing 6 fastened on the side support 4. The record carrier rests at one spot on a wing 7 of a guide wall flap 8 and later at another spot on a support 9. 
     The tractors shown in FIGS. 1 and 2 have pivoting bearings 11 for the two different hinged parts. According to FIG. 1, the hinged part consists of a cover flap 12 pivotable about a pivoting bearing 11. According to FIG. 2, the hinged part consists of the guide wall flap 8, which is likewise pivotable about a pivoting bearing 11. While the guide wall flap 8 can be swung in the direction indicated by an arrow 13 for shipping or packing, swinging out and in of the cover flap 12 is for putting in the edge-punched record carrier--i.e., the edge-punched paper web. The paper web is put with its pin holes on pins 14 of belt fastener 5, which is carried in tractor body 16. Then cover flap 12 is swung from the vertical position shown to the horizontal position, in which it covers belt fastener 15. 
     Each of the pivoting bearings 11 comprise pivot pins 17 in the form of spring steel wire pieces 18 cut to length. Tractor bearings 16a and 16b containing bores 16d in which ends 18a and 18b of spring steel wire piece 18 are mounted are provided on the tractor body 16 separated in the advance direction 19. The hinged part (i.e., either the guide wall flap 8 or the cover flap 12) carries two hinged part bearings 10a and 10b which in each case are provided with a through-hole 10c. 
     The spring steel wire piece 18 runs in through-holes 10c. The hined part bearings 10a and 10b have outside, planar surfaces 10d which rest on a planar counter surface 16c on the tractor body 16. The spring steel wire piece 18 is straight in its relaxed condition, but it is slightly bent when put through the through-holes 10c. That is, the spring steel wire piece 18 is put under spring tension. This tension is achieved by an offset of about 0.8 mm between the axes of the through-holes 10c and the axes of the bores 16d in the tractor bearings 16a and 16b. The planar surfaces 10d on the hinged part define the open and closed end positions of the hinged part, and the spring steel wire piece 18 alternately resiliently biases the hinged part towards each of the two end positions. As the hinged part is pivoted from one end position to the other, the spring steel wire piece 18 passes through an over-center position. 
     The effects described are obtained by at least one tractor bearing (16a or 16b) being provided on-center on tractor body 16, while the hinged part swings relative to the tractor body 16 on the hinged part bearings (10a, 10b). 
     The spring steel wire piece 18 is preferably pinched at its ends 18a and 18b to prevent its falling out of the tractor bearing 16a and 16b. 
     For putting in the paper web or for packing it, it is advantageous if the cover flap 12 can be put upright--i.e., vertical and fixed. For this purpose, the outside, planar counter surface 16c on the tractor body 16 runs at 90° to the corresponding surfaces 10d of the hinged part bearings 10a and 10b on the cover flap 12. 
     The principle of this invention can be applied both for the cover flap 12 for the belt fastener 15 and for the guide wall flap 8 for the record carrier. 
     Additionally, this principle can be applied to all flap parts of a printer, particularly of a dot matrix printer.