Ink duct for tubular styluses
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an ink duct for tubular styluses. 
     2. Description of the Prior Art 
     It is customary, for tubular styluses, to employ spiral compensating systems, which have the disadvantage that in the case of an ink storage volume in excess of 1.5 cm 3  the spiral system reacts too sluggishly to temperature fluctuations and undesirable drop formation occurs at the tip of the writing tube. 
     German Offenlegungsschrift No. 3,205,800 discloses an ink duct system for ink drawing implements with a spiral, labyrinthine ink compensation means, or provided with longitudinal chambers, with axially movable drop weight with cleaning wire and writing tube, in which the ink compensation means has in its internal bore, or the drop weight on its envelope surface, at least one capillary groove multiply subdivided in the longitudinal direction, which extends as a relatively low-capillary ventilation capillary from the connecting tube to a narrower air control point located in the lower half of the ink compensating means and is passed below ink control point as a high-capillary connecting capillary to the writing-tube, whilst an axially oriented ink capillary is in communication with the air control point. The ink duct system has no lamellae, but a spiral system. 
     The documents of German Utility Design No. 7, 633,429 relates to a writing tip for tubular writing implements with drop weight and securing element, in which an optionally spring-like connecting element, which is provided between drop weight and securing element, is constructed integrally with, or otherwise firmly connected to, both the parts. 
     The aim of the invention is to propose an ink duct system which reliably controls a volme of ink in excess of approximately 1.5 cm 3 , such as is demanded for a non-refillable drawing implement for example, and therefore reacts more sensitively to temperature fluctuations and nevertheless embodies the advantage of vibration resistance in the spiral system. 
     SUMMARY OF THE INVENTION 
     The mode of achieving this aim is disclosed by the technical teaching described in the characterized clause of patent claim 1. 
     Other advantageous further developments are set forth in the subordinate claims. 
     A similar system is known from German Offenlegungsschrift No. 3,338,227, where a compensating element with lamellae is employed, in which air access to and escape from the lamellar system is effected by two air grooves arranged parallel to the central air groove. 
     This is achieved by prolonging the plug-on sleeve with a head piece, that is to say a tubular element on which a lamellar system is integrally shaped, which is maintained on a plug-on stud by frictional engagement. This plastic lamellar element serves with its bore to house the writing tube. The bore is widened to the rear and the wire housing is mounted movably therein. It is of the utmost importance for the function of this system that the capillary ink supply system which supplies inks to the annular gap in the writing tube does not exhibit widened parts in any region, because the supply of ink to the annular gap in the writing tube would be threatened thereby. 
     In the region of the perforation which connects the capillary gap to the bore, due to the movable mounting of the wire housing it must be ensured that the ink flow does not break off at this point. Where a drop weight is employed there is the danger that when the implement is held obliquely, in the writing position for example, the wire housing closes the bottom perforation and the ink flow thereby breaks off. In order to prevent this, it is advantageous to shape longitudinal fins of small-width integrally in the bore, which guide the wire housing closely and prevent the perforation from being closed. 
     In order to secure also the transfer of the ink into the plane gap, it is advantageous here again to limit the movement of the wire housing by integrally shaped cams which are located on the annular plane surface. 
     In order to secure the connection from the plane gap to the annular gap in the writing tube, it is further advantageous to make the rear end of the writing tube extend as far as the plane gap. The integrally shaped cone on the writing tube, the cone of the wire housing and the regulating wire thus secure the regular flow of ink to the tip of the writing tube. 
     It may be necessary from considerations of cost to omit the drop weight and to provide only a spring which is advantageously shaped integrally on the wire housing made of plastic, and retains the regulating wire in the correct functional position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. I-IV and Va-f illustrate embodiments of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. I shows a plastic lamellar element 3 with a flange 3l, an annular gap 3f, an air groove 3g, a capillary gap 3d, chambers 3n, lamellae 3m, capillary grooves 3s, a plug 8 and a writing tube 1. 
     FIG. II shows a writing tube 1, the plastic lamellar element 3, the flange 3l, the lamellae 3m, the chambers 3n, an air groove 3i, ventilation grooves 3h, a transverse groove 3k, the plug 8 and a part of a storage tank 10. Webs are designated 3t. 
     FIG. III shows a longitudinal section through the writing element. Visible are the writing tube 1 and its bore 1a, an annular gap 9a in the writing tube 1, a regulating wire 5, a conical bore 1b in the writing tube 1, a bore 3b in the plastic lamellar element 3, an annular gap 9b between conical bore 1b and cam 3r, a wire housing 4, the plastic lamellar element 3, a bore 3a in the plastic lamellar element 3, an annular gap 9d, longitudinal fins 3p, a bore 4d in the wire housing 4, an external diameter 4c of the wire housing 4, the stroke path 9e of the wire housing 4, the rear end 4e of the wire housing 4, the capillary grooves 3s, a drop weight 6, the capillary gap 3d, the air groove 3i, the plug 8 with a bore 8a and with an annular plane surface 8b, the transverse groove 3k and the air groove 3g. The capillary perforation is designated 3e, whereas 3f represents the regulating gap. FIG. III also shows the section positions of the cross-sections a--a, b--b, c--c, d--d, e--e, f--f. 
     FIG. IV likewise shows a longitudinal section through the writing element. In this drawing the wire housing 4 may be seen with an integrally shaped plastic spring 4f. A cone on the wire housing 4 is designated 4a, whilst 8c identifies the plug for a construction with spring 4f for the wire housing 4. The reference numeral 4b designates an annular plane surface of the wire housing 4, and 9c a plane gap between 3c and 4b. 3c is an annular plane surface. All the remaining reference numerals correspond to FIG. III. 
     FIG. Va shows the cross-section a--a according to FIG. III, in which the external diameter 4c of the wire housing 4, the bore 3a in the plastic lamellar element 3, the longitudinal fins 3p and the annular gap 9d are visible. 
     FIG. Vb shows the cross-section b--b according to FIG. III, in which the drop weight 6, the wire housing 4, the chambers 3n, the air grooves 3i and 3g and the ventilation grooves 3h, the regulating gap 3f and the perforation 3e are visible. 9d is the annular gap and 3t are the webs. 
     FIG. Vc illustrates the cross-section c--c, in which the drop weight 6, the wire housing 4, the chambers 3n, the air grooves 3i and 3g and the ventilation grooves 3h, and also the webs 3t are visible. 
     FIG. Vd shows the cross-section d--d, in which the transverse groove 3k, the plug 8, the capillary gap 3d and the air groove 3g are visible. 
     FIG. Ve shows the cross-section e--e, in which the drop weight 6, the plug 8, the air grooves 3i and 3g, the capillary gap 3d and the ventilation grooves 3h are visible, and lastly 
     FIG. Vf shows the cross-section f--f according to FIG. III, in which the cone 4a of the wire housing 4, the annular plane surface 3c with the cams 3r shaped integrally on this plane surface are visible. 
     The function of the ink duct according to the invention is as follows: 
     The ink flows from the storage tank 10 into the capillary gap 3d, into the perforation 3e, fills the regulating gap 3f and the capillary grooves 3s, flows via the annular gap 9d, the plane gap 9c, the annular gap 9b in the cone and the annular gap 9a to the tip of the writing tube. Lastly, the air groove 3g also becomes partially filled with ink. When ink is consumed during writing or drawing, a negative pressure occurs in the storage tank 10, which negative pressure draws the ink out of the air grooves 3g and the regulating gap 3f and allows the air which is present in the air groove 3i and 3h to flow into the storage tank 10 until pressure equalization occurs from the storage tank internal pressure to the ambient air pressure. When pressure equalization has been achieved, the ink in the regulating gap 3f closes the air access to the storage tank 10. When the air volume in the storage tank 10 is increased by heating or by pressure difference, the ink flows, the regulating gap 3f being closed, via the capillary grooves 3s into the chambers 3n which are reduced in cross-section to-wards the rear, and the ventilation grooves 3h, until the pressure between storage tank 10 and ambient air has been equalized, without drop formation occurring on the tube tip. If ink is consumed by writing in this state, then the ink is first sucked out of the chambers 3n via capillary grooves 3s. Only when the latter have been exhausted does the regulating gap 3f open the passage for the air and allow the latter to enter the storage tank 10 via the air groove 3g. Consequently even a tubular stylus with a large charge volume, in the case of a non-refillable writing implement for example, is controlled reliably by this system in the case of pressure differences and with the required vibration resistance.