Source: {"pile_set_name": "USPTO Backgrounds"}

Hand-held blade tools are used in a wide variety of cutting and scraping activities in daily use.
For efficient operation, it is desirable that such tools be maintained with a sharp edge. For this purpose, it is known in the prior art for blade tools to utilize inexpensive disposable blades. For reasons of safety in storage, it is desirable that the blades of such tools may be shielded when not in use; for this purpose, it is known in the prior art for tools to employ a blade carrying member that is retractable within a housing and upon which a single disposal blade may be removably mounted. Examples of such prior art blade tools, for use in cutting and scraping operations, respectively, are shown in U.S. Pat. No. 4,761,882 (Silverstein), issued Aug. 9, 1988, and U.S. Pat. No. 2,601,723 (Keller), issued Jul. 1, 1952.
These types of single blade tools are known to be relatively economical to purchase and use, and to be relatively reliable in operation. However, in relation to both such tools, when the blade becomes worn, the operator is exposed to danger of injury from the sharpened edges of the blades during their replacement. As well, the blade replacement operation is relatively cumbersome and time-consuming, and typically requires the operator to cease whatever activity he or she is engaged in to effect the replacement of the blade.
Accordingly, a number of blade tools are known in the prior art which attempt to provide, in a safer, quicker and more convenient manner, for a replacement supply of new blades to be interchanged as required.
One example of such a prior art blade tool is that shown in U.S. Pat. No. 4,277,888 (Szabo), issued Jul. 14, 1981, which discloses a utility knife having a magazine in which a plurality of blades are stacked, a blade changing device which pushes a blade from the top of the stack into an operating position, and pulls said blade underneath the stack when it has become worn. Such an arrangement resolves the aforementioned safety concern to a large extent, and provides for relatively quick blade exchange, albeit, requiring two hands to effect such exchange. However, this design suffers from undue complexity of assembly, and unduly high production costs. As well, this design suffers in that utility knives are often used for tasks wherein the blades become soiled or coated with foreign material, which soiling and coating tends to impair the reliability of the blade exchange operation. Finally, the utility knife disclosed in this patent provides only for sequential access to the replacement blades, which can result in a blade which is slightly worn, but still acceptable for normal use, being prematurely exchanged in circumstances where a very sharp edge is required for a particular and infrequent use.
U.S. Pat. No. 4,615,118 (Ihata), issued Oct. 7, 1986, discloses another common type of utility knife. The knife described in the Ihata patent comprises a magazine portion which can be fitted into a magazine storage cavity that extends within a rear portion of the knife. A plurality of strip-like blades having pre-stamped lines of breakage at uniform spacing are fitted within the magazine. A respective one of the blades may be selectively extended so as to present a front portion of the blade for use. When said front portion of the blade has become worn and unusable, the blade may be broken along the foremost line of breakage, and an unused portion of the blade may then be extended for use. This type of knife is economical to purchase and operate, and provides for convenient retraction of the blade for storage. However, the danger of injury in the prior art is continued in this design, as the spent strip blades must be fully extended to the front of the knife and manually removed, so that the next strip blade may be engaged. As well, the removal of the blade sections exposes the user to the additional risk of injury from metal fragments.
U.S. Pat. No. 5,604,984 (Shepherd et al.), issued Feb. 25, 1997, shows another prior art utility knife. The utility knife disclosed in the Shepherd patent comprises a cylindrical blade magazine removably mounted in a manually holdable housing and rotatable about an axis parallel to a longitudinal axis of the housing, the housing having a slidable transport mechanism which carries a blade from the magazine into an operative position, and returns same to the magazine for storage. Rotation of the blade magazine causes the retracted blade to be removed from the transport mechanism, and a new blade to be engaged by the transport mechanism, for subsequent movement of the new blade from the magazine into the operative position. The Shepherd knife resolves the aforementioned safety concern, and as well, allows for selective, non-sequential and relatively convenient access to the plurality of blades stored in the magazine. However, this knife maintains the problem of unduly high production costs, and also suffers from the requirement that the rear portion of the knife must be of a rather large bulbous shape to contain the cylindrical magazine, which is an impediment to the production of an ergonomically friendly and aesthetically pleasing knife. As well, the complexity of the blade magazine employed in this knife necessitates a high-replacement value, resulting in unduly high operating costs for this knife.
Moreover, none of the known prior art blade tools having a plurality of blade members which may be conveniently exchanged without risk of injury provide for scraper blades of the type shown in the Keller patent, wherein the sharpened edge of the blade in use is presented in an orientation normal to the handle. Rather, such prior art blade tools provide for the sharpened edge of the blade in use to be presented in an orientation substantially parallel to the handle, only, which does not particularly suit them for use in scraping operations.