BACKGROUND of the INVENTION
Field of application
The present invention is directed to lawn rakes in general and more particularly, lawn rakes having a cross head assembly with tines that are replaceable.
Discussion of the prior art
The following description and discussion of the prior art is undertaken in order to provide background information so that the present invention may be completely understood and appreciated in its proper context. The discussion is provided in terms of specific prior art references and an overview of trends that have developed within the art of broom-style lawn rakes that have tended to limit the effectiveness of lawn rakes.
The prior art of broom-style lawn rakes clearly shows an early period where a cross head assembly or cross head was a defining element of the lawn rake, leading to the period where a rake head assembly or rake head became a defining element. The defining element of a cross head assembly or cross head is a transverse member fixed to the end of a handle, with the tines arranged along and extending away from, the transverse member. The tines are generally parallel to one another and perpendicular to the transverse member. The defining feature of a rake head assembly or rake head, as taught by the prior art, is a fan-shaped or triangular shaped assembly of tines, diverging radially away from a fixed point at the end of the handle. While true cross head type rakes dominated the early prior art, a transition took place which embodied the transverse member with curvature. Further development of the art resulted in the rake head type rakes that prevail in the recent art.
As early as U.S. Pat. No. 566,048 issued Aug. 18, 1896 to A. Woeber for a "Rake or Broom," the indicated rake shows a cross arm through which the tines passed to meet and join at a grooved, segmented head. Already this reference is teaching that one end of the tines can serve the purpose of gathering leaves while the other end merges together with other tine ends to form a structural framework and anchoring. This teaching is contrary to a true cross head which has the sole function of structurally mounting and supporting each tine, while each tine has the sole function or gathering and collecting leaves and lawn debris.
U.S. Pat. Nos. 1,614,385 issued Jan. 11, 1927 to M. W. Otto for a "Rake," 1,621,276 issued Mar. 15, 1927 to F. E. Richardson for a "Rake," 1,735,237 issued Nov. 12, 1929 to E. L. Dennis for a "Garden Tool," 1,831,009 issued Nov. 10, 1931 to H. G. Kimber for a "Rake," 1,933,636 issued Nov. 7, 1933 to A. Montan for a "Rake," 1,942,629 issued Jan. 9, 1934 to W. Withington for a "Broom Rake," and 1,970,616 issued Aug. 21, 1934 to A. Montan for a "Rake," are all examples of cross head construction. All of these rakes have a relatively complicated cross head structure. All have metallic cross heads and metallic tines. Two more recent cross head art patents are U.S. Pat. No. 4,376,367 issued Mar. 15, 1983 to Elias L. Rocquin for a "Rake," and U.S. Pat. No. 4,649,698 issued Mar. 17, 1987 to Neil. Sykora for a "Lawn Rake." Both of these patents also rely on complicated metallic assemblies. Thus, it is apparent that the cross head art never made a transition to plastic materials that was accomplished in the transition of rake head assemblies having a large number of individual metal tines and other components connected together, to a simple, single-piece, injection molded plastic rake head with integral tines. The cross head art consequently did not take advantage of the lower densities of plastic materials that enable much lighter rakes. Undoubtedly, the ability to create a single-piece rake head was a driving force in the transition to plastic. At the same time the inability to create a single-piece cross head forestalled any attempts to move to plastic in cross heads.
The Rocquin patent and Sykora patent also both cite replaceability of tines as a salient feature, but the replaceability is achieved by complex arrangements requiring customized machining and metalforming of components. The Rocquin and Sykora patents, like others listed above, also rely on channel-like metal cross arms that increase weight and are difficult to manufacture. In addition, the method of assembling the handle to the cross arm requires a metal custom-made piece attached to the cross arm to receive the handle.
The cited Richardson patent is a further specific example of why cross head art evolved into rake head art, at the same time illustrating a deficiency in rake head art. Richardson indicates in the specification that the slots to receive the tines ". . . may be arranged in lines parallel with the broom handle . . . ," but admits that the drawing figures show them arranged in lines diverging from the handle. With the tines parallel to the handle, the width of the rake is limited to the width of the cross head. By making the cross head with the tines divergent, the raking width of the rake can be increased beyond the width of the cross head, thus increasing raking capacity. When carried to its ultimate by the prior art, a rake head assembly evolved, with the tines radiating and diverging from a common point.
This approach does increase raking capacity. The process was driven by the use of metal components which significantly increased the weight of a rake to increase its capacity. However, tines which diverge in any manner introduce a significant structural disadvantage. When drawn across the ground, divergence of the tines causes an eccentric or unbalanced loading to be placed on the tines which makes the rake difficult to control and can shorten the useful life of the tines. Tines which diverge the most, experience the greatest eccentric loading. In addition, the outside tines may be longer, thus more flexible, and thus less effective in raking leaves.
The rake head type rakes partially solved this problem by an intermediate cross member generally parallel to the ground and located between the handle and the tine ends. This cross member stiffens each tine by tying all tines together to provide lateral stability to each tine. This member adds complexity to the lawn rake and usually requires a separate stiffening spring to function properly. U.S. Pat. No. 5,022,221 issued Jun. 11, 1991 to David R. Bonnes and Philip J. Male for a "Lawn Rake with Improved Spring Anchoring," is a recent example of the efforts to provide an intermediate member to stabilize and control flexing of tines. Such arrangement inherently reduces and even eliminates the capability for replacing tines.
With a cross head, tines which instead are parallel to the handle bend primarily within the plane of the tine. That is, the tines undergo single axis bending for straight-ahead raking, minimizing torsional bending. Each parallel tine also generally experiences the same loading. The limiting factor for the raking capacity of a lawn rake with a cross head then becomes a simple matter of the width of the cross head, which in turn is limited only by the weight and strength of the transverse member which forms the cross arm. The metal channel-like cross arms utilized extensively in the prior art did not maximize strength-to-weight ratios which is essential for a cross head type lawn rake with a wide width, and which can be achieved with a cross arm made from a tube that has a closed cross section.
The tines of the Dennis patent are cited as replaceable, but the metallic nature of the tines suggests considerable pressure is required for their release and replacement. The tines of the Montan patent, U.S. Pat. No. 1,933,636, are disclosed to be of a self-locking type but it is not clear again whether the tines are removable. The Withington patent refers to removable tines made from spring steel having notches to lock the tines in position. Any notch of this type is a point of incipient weakness and failure. Furthermore, any deformation of the tine, at the notch or elsewhere, would render the tine difficult, if not impossible, to remove from the slots of the cross head. The cross head is of a metallic channel configuration arcuately bent to position the tines in a diverging fashion. The forming of the cross head requires additional steps in the manufacturing process that increases cost.
A rake having a cross bar and highly flexible spiral coiled tines is described in U.S. Pat. No. 2,095,693 issued Oct. 12, 1937 to H. E. Fuller for a "Rake." It appears the tines of this rake have too much flexibility and the art may have been better served if the coil of each tine wrapped around the cross bar instead of floating freely with only the tine end secured. Fuller's later patent, U.S. Pat. No. 2,302,541 issued Nov. 17, 1942 for a "Lawn Broom," appears to be an improvement over his earlier spiral tine. The method of securing the integral pairs of the tines provides greater lateral stability. However, the overall functionality of the tines under arduous raking conditions is still question able due to the coiled nature of the tine.
U.S. Pat. No. 2,075,220 issued Mar. 30, 1937 to S. P. Neuhausen for a "Rake," discloses a channel cross head having apertured flanges with the tines arranged in integral pairs. The tines however, must be held in position by a continuous rod which engages all of the tines. Thus, the tines are not easily removable and clearly not individually removable. J. L. Owen in U.S. Pat. No. 2,156,480 issued May 2, 1939 for a "Rake," shows a rake with tines that diverge outwardly except for the two central tines which converge inwardly. The tines are all of the same length, and thus are interchangeable in addition to being removable as described. As in the Fuller patent, however, a rod must be disengaged from the tines in order to achieve removability of each tine.
U.S. Pat. No. 2,850,865 issued Sep. 9, 1958 to E. B. Anderson for a "Lawn Rake," is directed to a lawn rake with a U-shaped cross bar having apertures in each cross bar flange aligned transversely. The spring steel tines are individually inserted into the aligned holes, with the coiled end of the tines frictionally engaging the cross bar by a snap fit. The tines are thus individually removable. Once again the cross bar is a channel-like member having an open cross section that is structurally inefficient. Furthermore, the frictional engagement of the tines, or the solidly attached engagement seen in other patents, raises the question of how the long unbraced length of the tines can withstand arduous raking without being bent or broken, especially when coming in contact with an object on the ground such as a stone.
With the flat tines employed in the Anderson patent and many other cross head patents, the weak axis of the tines is oriented in the direction of raking. The fixed connection of the tines to the cross bar also creates high stress where the tines are attached to the cross bar since the tines are behaving as a cantilevered beam having a fixed, moment resisting support. The highest stress in the tines then occurs where the tines are fixedly attached to the cross bar. There is a need to decrease the stress in the tines at this point by either increasing the strength of the tines in the direction of raking, or by decreasing the bending moment that the tines experience at the juncture with the cross bar, or a combination of both.
The Rocquin patent, referenced earlier, describes a lawn rake with a cross arm and individually replaceable tines. Rocquin makes the point that tools are not required to replace a tine. Nevertheless, a retaining strip is required to secure each tine in place. It is entirely conceivable such a retaining strip can be dislodged and lost amid a pile of leaves during raking. Loss of a retainer would reduce the effectiveness of the rake the same as if a tine broke. However, with the loss of the retainer, the tine could not be replaced, defeating a main object of the invention.
An early patent, U.S. Pat. No. 567,129 issued Sep. 8, 1896 to L. Gibbs for a "Rake and Apparatus for Making Same," discloses a method of manufacturing tubular rake heads. In this case a strip of sheet steel is punched with pairs of holes, the strip bent into a U-shape, tines inserted through aligned pairs of holes, and the U-shape further bent into a round tube. The tines become permanently and fixedly attached to the cross head during this process, due to the mechanical locking provided by the last bending. This method is intensive of special tools and dies, and does not render the tines replaceable. The slit that remains in the tube after bending results in the tube having a cross section which is not closed, thereby significantly reducing the strength of the cross head.
Another limiting factor in the development of a more efficient lawn rake, either cross head or rake head, has been the inability of a rake to be manipulated with a sideways component of motion. Thus, raking has been effectively restricted to straight-ahead raking action. The cross head art that has been cited does include references to tines having a circular cross section. Tines which have a circular cross section are uniformly flexible in all directions. However, the trend of recent art has been to use rectangular tines with intermediate stiffening ribs, or with intermediate stiffening ribs and stiffening springs. The Bonnes and Male patent cited earlier is a good example.
This trend started with the use of spring steel having a rectangular cross-section in order to minimize the connection problem at the point of convergence of the tines, for a fan-shaped rake. The rectangular cross-section then migrated to the single-piece, injection molded rake head. With rectangular tines the wide part of the tines is oriented parallel to the head of the rake. The tines are therefore far stiffer in a direction parallel to the rake head, than perpendicular to it Hence, raking action naturally advances only perpendicular to the rake head. Intermediate stiffening ribs reinforce this limitation. Lateral, or sideways, or swirling, or circular movement of the rake is made prohibitively difficult as long as the tines are in contact with the ground.
The cited cross head art that did utilize tines having a circular cross-section, also relied on fixed termination of the end of each tine not in contact with the ground. With such a fixed connection, tines that are deflected sideways undergo torsional bending, as well as bending in two planes. As said by Jonas Leander Owen in U.S. Pat. No. 2,156,480 issued May 2, 1939 for a "Rake," " . . . the tines in both forms of construction are continually secured against shifting in all directions and can neither turn nor shift laterally . . . ". This same condition has propagated throughout the art, showing the effort that has been made to always fixedly resist all applied forces. The success of this effort has severely limited the flexibility and ease of use that can be exploited by alternative constructions.
Thus, it can be seen that the prevailing trend in the art has gone from cross head art with metal tines having either a circular or rectangular cross-section, to rake head art with metal rectangular tines, to rake head art having rectangular tines integrally molded into a single-piece injection molded rake head. For all of the above reasons, it is apparent the prior art has not been able to provide a lawn rake having a cross head assembly that is simple to manufacture, makes use of parts that do not have to be entirely custom made, minimizes the number of parts, minimizes the loading conditions of the tines, and makes use of plastic materials. Furthermore, the prior art also has not explored the use of individually installed and replaceable plastic tines, or the use of tines that are loosely mounted on the cross arm or cross bar, allowing freedom of movement that tends to minimize stresses in the tines during raking. The prior art also has not explored the use of tines that are self-releasing from the cross arm during raking action under predetermined loading conditions, to minimize possibility of breakage. The prior art has not investigated whether a plastic cross head with individual plastic tines can be utilized since the prior art had already shifted to the rake head assembly and rake head style of rakes by the time plastic became established as a material of choice. With this discussion, the following objects of the invention are set forth.
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