Draw string fitted sheet with curved hem for even tension
This application is a continuation of application Ser. No. 08/280,778 filed Jul. 26, 1994, which is now abandoned. 
    
    
     FIELD 
     The field of this invention relates to bed cloths or sheets, particularly fitted sheets with draw strings. 
     BACKGROUND 
     Fitted sheets have been designed in the past in the attempt to overcome a few basic problems involved with securing and tensioning the sheet. The problems include holding the sheet in place on the mattress; holding the sheet tight and wrinkle free across the top face of the mattress and at the same time providing for their easy removal and replacement. 
     The most popular design and the one in use over much of the world is the elastic corner design. This design provides for the easy application and removal of the sheet but does not anchor the sheet securely; they often come loose and are never held completely tight across the face of the mattress. 
     PRIOR ART 
     The long list of patents concerning draw string sheets include many design attempts to solve these simple problems. These designs have failed to solve all these problems at the same time. The most valid prior art list includes the following: 
     Beer U.S. Pat. No. 3,858,256 Jul. 7, 1975 is a very complicated attempt at securing and tightening the sheet. It requires a prohibitive amount of fabrication difficulties and material expense. It would also be very time consuming to apply to a bed. And unlike the design covered by this application the hem where the straps are secured when installed are parallel to the sides of the mattress providing no tension across the face of the sheet. 
     Monier U.S. Pat. No. 3,900,909 Aug. 26, 1975 requires that each corner of the bed be accessible and also requires that each corner be secured and removed one at a time causing considerable frustration. Also this design lacks any means to provide tension anywhere other than the corners. 
     Joyce U.S. Pat. No. 4,727,608 Mar. 1 1988 describes a system where a pre-curled plastic insert in the sheets hem draws the sheet tight when it returns to its&#39; performed curve when applied to the mattress. It is doubtful that this design would actually work, but if it did, the installer would have to lift the side of the mattress in order to allow the sheet to slide under. The same would be true at removal with perhaps even more difficulty struggling with the resistant insert while holding the mattress up for access. 
     Davis U.S. Pat. No. 4,970,744 Nov. 20, 1990; Etherington U.S. Pat No. 5,020,177 Jun. 4, 1991; Chamberlain 5,046,207 Sept. 10 1991, all provide a slightly easier way to apply and remove the sheets but the drawstring is still difficult to access. Also the shape of the hem when installed is parallel to the sides of the mattress causing a gathering of the hem only at the corners and providing no tension across the face of the mattress. 
     OBJECT OF INVENTION 
     It is the object of my fitted sheet is to provide a simple and inexpensive means of releasably securing the sheet in position on a mattress. It is also an object of ny fitted sheet to provide a means of tensioning the sheet and eliminating the tendency of the sheet to become wrinkled when slept on. 
    
    
     Other objects and advantages of my fitted sheet will be readily appreciated by those with ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the following drawings in which: 
     FIG. 1 illustrates an approximate pattern for the material used to form the main body of the sheet. 
     FIG. 2A illustrates, from below, the fitted sheet fully fabricated in position to be placed on the mattress. 
     FIG. 2B illustrates, from below, the fitted sheet installed on the mattress with the draw string tight. 
    
    
     SUMMARY 
     In accordance with the present invention a drawstring sheet comprises a peripheral hem containing the drawstring strategically curved in sections where it falls adjacent to the lower edges of the mattress to distribute the generation of tension forces along the lower edges and away from the corners. 
     DESCRIPTION 
     These embodiments illustrated in all the figures are fabricated in the same manor as anyone skilled in the art will have made other fitted sheets except what is specified below. The materials except differences specified will also remain conventional. 
     FIG. 1 shows the approximate pattern for material used for the main body of sheet. The particular feature of note is the shape of edges 3. Edges 3 are shaped in a substantially concave curve which is crucial for the proper function of this invention. Edges 3 are positioned to fall substantially under the mattress when sheet is in its final position on mattress. The pattern may be sized and proportioned to accommodate any of the many mattress sizes available. Broken lines 4 and 5 represent where material is to be bent or folded. Broken lines 5 are where material is bent to form the sides of the envelope corresponding to the sides of the mattress. The material is bent lip 90 degrees at line 5 and sewn to the adjacent side at each end 6. The hem which holds draw string 7 and 8 seen in FIGS. 2A and 2B is formed by folding the edges 3 at broken lines 4. Hem 3 may also be made separately of an appropriate low friction material and sewn on edges 3. 
     FIG. 2A shows my fitted sheet fully fabricated and a in position to be placed on a mattress. Draw strings 7 and 8 run through each hem 9 in sequence around the sheet and exit the hem at openings at position 10. In other embodiments only one string may be used. In this case, openings need only be provided on one side of the sheets. Quick release clasps, of the many types available, can be added at positions 10 to hold draw strings 7 and 8 tight. 
     FIG. 2B shows the fitted sheet in position on mattress 11, with draw strings 7 and 8 tight. The shape of hem 9 is seen here to resemble an ellipse characterizing the key feature of this invention. 
     OPERATION 
     The operation of my fitted sheet is simple. The sheet is placed over mattress, the hems with the draw strings are tucked under mattress and the draw string is then pulled tight and fastened. 
     CONCLUSION AND RAMIFICATIONS 
     With the broad use of my fitted sheet, the problem of fitted sheets coming loose and/or becoming wrinkled on the bed can be eliminated. 
     This is only one of the preferred embodiments of my fitted sheets. Many possibilities exist that may fulfill the object of this invention, the scope of which is covered in the following claims.