Patent Publication Number: US-4544296-A

Title: Disposable propel-repel pencil

Description:
This is a continuation of application Ser. No. 947,580, filed Oct. 2, 1978, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to mechanical pencils and in particular to mechanical pencils composed of a relatively few, simple inexpensive components readily adaptable to automatic assembly specifically for sale as a disposable writing instrument. 
     2. Description of the Prior Art 
     Previous designs of mechanical pencils that employed a helical coil rotatable inside a hollow barrel have either utilized split tubes surrounding the lead, or pushers which are disposed in the interior of the coil or split tube. Such prior pushers had radially extending projections which engaged the coil or barrel. These constructions necessitated threading the pusher into the coil or split tube to the proper position at assembly and therefore required the design of relatively complex and expensive machinery to accomplish the assembly of the various components. 
     Other types of pusher which engaged the coil about its turns were constrained by a separate guide means positioned within the barrel of the writing instrument. Here it was necessary to physically interconnect the pusher with the guide means as well as interconnecting the pusher with the coil, all of which entailed complex and expensive structures and methods of assembly. 
     Examples of such prior art are disclosed in U.S. Pat. Nos. 966,712 to C. A. Smith, 1,539,468 to Cook et al., 2,866,438 to Schischkow and 3,630,628 to Roman. 
     Accordingly, it is the object of the present invention to provide a mechanical pencil employing relatively few components, each of which is inexpensive and readily assembled by simple machines. 
     More specifically, it is the object of this invention to provide a mechanical pencil of such simplicity of structure, minimum number of parts, adaptability for automatic assembly and low cost of manufacture as to permit optional discarding of the pencil after the initial lead has been consumed, thereby eliminating the necessity of the user keeping a supply of spare refill leads and undergoing the sometimes tedious process of replacing the refill leads in the pencil with the attendant possibility of lead breakage during this process. The mechanical pencil of the present invention by its simplicity and low cost of manufacture hence is competitive with other disposable writing instruments. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a mechanical pencil that includes a barrel having a non-circular bore, a rotatable helical coil fitted within this bore, an external driving member attached at the rearward end of the barrel and operably connected to the coil, and a lead positioning means or pusher member interposed between the exterior convolutions of the coil and the interior bore of the barrel. The pusher is configured to engage the turns of the coil from about its exterior surface and is constrained within the non-circular bore for longitudinal sliding movement within the barrel so that rotation of the driving member that is connected to the helical coil will cause longitudinal translation of the lead positioning means within and relative to the barrel. 
     Stop fins on the interior portion of the pusher extend through the turns of the coil and engage the rearward end of the centrally located writing lead and serve to provide the contact to propel the lead forwardly and thereby project it from the front end of the pencil to maintain the proper lead extension for writing purposes as the lead is worn away during use. 
     The lead positioning means or pusher also includes gripping fins spaced forwardly from the stop fin and adapted for elastic transverse displacement to frictionally engage the writing lead so that retraction of the lead may be accomplished by reverse rotation of the coil relative to the barrel. The lead positioning means has a longitudinally extending guide rail that is disposed within a longitudinal extending channel or groove portion of the non-circular bore of the barrel to provide the means to translate the rotary movement of the coil into longitudinal movement of the lead. The lead positioning means is a separate unit positioned within the main internal bore of the barrel in captive spaced relation between an internal wall portion of the barrel and the exterior configuration of the coil and is operatively associated solely by abutting contact between said members. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the mechanical pencil of the present invention. 
     FIG. 2 is an exploded perspective view of the principal component parts of the pencil of the present invention. 
     FIG. 3 is an exploded perspective view showing the lead positioning means, a section of the coil, and adaptability of opposite end of the lead positioning means to receive leads of a different size. 
     FIG. 4 is a transverse cross section of the mechanical pencil taken along lines 4--4 of FIG. 1. 
     FIG. 5 is a partial, broken, longitudinal cross-sectional view of the mechanical pencil of the present invention taken along lines 5--5 of FIG. 4. 
     FIG. 6 is a partial, broken, longitudinal cross-sectional view of an embodiment of the mechanical pencil of the present invention similar to FIG. 5 that utilizes a larger diameter lead. 
     FIG. 7 is a partial, longitudinal cross section showing the drive member assembled with the rear of the barrel. 
    
    
     DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT 
     The mechanical pencil of the present invention includes an elongated hollow barrel 10, terminating in a frusto-conical tip section 11. As shown in FIGS. 4, 5 and 6, the barrel includes a main generally hexagonal bore 12 having three equally spaced inwardly extending ribs 13. The internal generally hexagonal bore 12 of barrel 10 changes at shoulder 14 to a forward generally triangular cross section 15 which terminates at shoulder 16. A forward conical bore 17 has a terminal tip 18 which is of a diameter approximately equal to the diameter of the writing lead. 
     As shown in FIGS. 2 and 7, the driving member 19 is basically a tubular member consisting of an external forwardly extending sleeve portion 20 fitted over and in rotational engagement with the rearward end 21 of barrel 10. Internal circumferential groove 22 on sleeve portion 20 co-acts with external circumferential ring 23 of barrel end 21 to provide a snap fitted rotational fit between driving member 19 and barrel 10, while preventing unintentional longitudinal disengagement of these components. Rearward facing tubular portion 24 of driving member 19 is adapted to frictionally retain an eraser 25. Extending forwardly from the eraser holder section 24 exterior to and overlying the barrel is an integral clip 26. Driving member 19 has an internal tubular section 27 extending forwardly into the rear of the internal bore of barrel 10. This tubular section 27 has an internal diameter which provides a press fit to the exterior of a helical coil 28, fitted in the internal bore 12 of barrel 10 and extending forwardly to the vicinity of step 16 in the forward end of barrel 10. Interposed in the space between the forward end of coil 28 and step 16 is a thin plastic washer 29 made of &#34;Mylar&#34; or similar plastic material. The inside diameter 31 of washer 29 is made slightly smaller than the lead diameter to positively grip the lead 32. Should the lead become broken between washer 29 and pusher 40 washer 29 provides sufficient friction on lead 32 to prevent it from falling out of the pencil; under this circumstance the propel function of the pencil remains and only the repel function is lost. 
     The outside surfaces of coil 28 contact internal bore surfaces 33a, 33b, 33c of barrel 10 as delineated in FIG. 4. 
     Interposed in one of the guide channels 34a, 34b, 34c disposed between ribs 13 of barrel 10 is a lead positioning means or pusher member 40. Referring now to FIGS. 2 through 6, the lead positioning means or pusher member 40 has an external longitudinal rail or rib 41 adapted to fit into one of the aforementioned spaces 34. The main body of pusher 40 consists primarily of fin portions 42 extending radially inwards between the turns of coil 28. A separate centrally located stop fin 43 also extends radially inward and projects beyond center line of coil 28, to provide a stop for the rearward end of lead 32. 
     Referring now to FIG. 3, forwardly disposed fin 44 of the lead positioning means or pusher 40 is bifurcated into two segments 44a and 44b which are elastic and laterally yieldable. These two segments form a gripping or clutch fin which segments overlie the diameter of lead 32 and engage the lead 32 with a frictional grip to prevent rotation and longitudinal movement relative to pusher 40. The leading fin portion at each end of the pusher 40 has a lead camming face 46 for guiding the lead 32 between the gripping fin portion 44a-b and 45a-b into contact with stop fin 43. 
     As shown in FIG. 3, the lead positioning means 40 is symmetrical about an axis that is at right angles to the longitudinal axis and centered about the central stop fin 43. Therefore, clutch fin 44a-44b can perform the same function as clutch fin 45a-45b. Thus the lead positioning means 40 of FIG. 3 may be installed in the pencil with either end forward. 
     In one form as shown in FIGS. 5 and 6, clutch fins 44a and 44b are of a different spacing than their counterparts 45a and 45b at the opposite end of the pusher 40. In this instance the pusher may serve in two different types of pencils, one of a standard lead size (0.046 inches diameter) as shown in FIG. 6 and the other of a fine line size (0.036 inches diameter) as shown in FIG. 5 merely by installing the pusher in the pencil with the desired end forward to co-act with the specific lead size chosen. In this instance, of course, the forward diameter in the terminal tip 18 of barrel 10 must be of the proper diameter for the lead size chosen. Such a change can be made by a minor change in core pins of the mold for barrel 10 when the barrel is made of molded plastic. 
     If it is desired that only one size lead be used in a pencil of this type, then both ends of the lead positioning means 40 can have the clutch fins formed with the same spacing and thus eliminate the necessity for any end orientation means in an automatic assembly operation. 
     In all instances, the lead positioning means 40 is fitted to the coil externally and the stop and clutch fins fit inbetween the turns of the coil without the necessity of the lead positioning means or pusher 40 being laced into the coil or, alternatively, threaded into the coil as is required in previous mechanism designs. Thus the lead positioning means or pusher 40 is held in operating position solely by its captive spacing between the exterior surfaces of the turns of coil 28 and the interior wall surfaces of the hexagonal bore 12. 
     OPERATION 
     In operation, clockwise rotation of the driving member 19 rotates the coil 28 resulting in longitudinal movement of the lead positioning means or pusher 40, since the pusher 40 is threadedly engaged with the exterior of the coil 28 and can not rotate in respect to barrel 10 because of the guide rail or rib 41 nesting in one of the guide channels or grooves 34 of the barrel 10. Stop fin 43 of the pusher 40 thereby forces lead 32 forwardly from the terminal tip 18. Conversely, counterclockwise rotation of the driving member 19 results in retraction of the lead 32 since clutch fins 44a and 44b or 45a and 45b keep the lead 32 frictionally retained within the fin portions by virtue of the transverse yieldable elasticity thereof. 
     It is understood that the writing instrument of the present invention may utilize various forms of marking elements other than graphite lead which are worn away by use, such as crayons and the like. Also, the writing instrument of the present invention may be used with marking elements that do not wear away through use, such as a ball point cartridge and the like which, when used, may be selectively projected from and retracted within the barrel. 
     It should be understood that the aformentioned embodiments merely illustrate the principles of the invention and modifications may be made in the specific structures without departing from the spirit and scope of the invention as set forth in the following claims.