AU2013100091A4 - Eccentric drive mechanism - Google Patents

Abstract

An eccentric drive mechanism enables smooth conversion of rotational motion to reciprocating motion. The mechanism includes a 5 housing (105) and a crank shaft (110) positioned at least partially inside the housing (105). The crank shaft (110) includes a first end (115), a second end (120) and a central portion (125), the first end (115) defining an eccentric bearing surface (130), the central portion (125) defining a concentric bearing surface (135), and the second end (120) defining a 10 concentric drive element (140). A first bearing (145) is positioned on the eccentric bearing surface (130). A second bearing (160) is positioned on the central portion (125) of the crank shaft (110) and also engages the housing (105). A pivot element (180) has a distal end (185), a driving end (190), and a pivot axis (195) located between the distal end (185) and the 15 driving end (190), the pivot axis (195) being fixed relative to the housing (110). Rotation of the crank shaft (110) causes the first bearing (145) to orbit a central longitudinal axis of the crank shaft (110), causing reciprocating motion of both the driving end (190) and the distal end (185) of the pivot element (180) about the pivot axis (195). C) N CN LrN 0N (C0 0) '7 1O 10) or

Description

P/00/012 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION INNOVATION PATENT Invention Title: "ECCENTRIC DRIVE MECHANISM" The following statement is a full description of this invention, including the best method of performing it known to me/us: 1 TITLE ECCENTRIC DRIVE MECHANISM FIELD OF THE INVENTION 5 The present invention relates to converting rotational motion to reciprocating motion. In particular, although not exclusively, the invention relates to an eccentric drive mechanism for driving a powered shearing tool. 10 BACKGROUND TO THE INVENTION The three types of mechanical motion include rotational motion, vibrational/reciprocating motion, and translational motion. In machinery it is very common to convert one type of motion to another type of motion in order to perform an intended task. For example, rack and pinion drives 15 are commonly used to convert rotational motion of a driving pinion gear into the linear translational motion of a part attached to a toothed rack. Also, rotational driving elements, such as a crank shaft or drill chuck have been used to power the vibrational or reciprocating motion of various tools, such as hand-held power sanders or powered shearing tools. An 20 example of such a device is described in Australian Innovation Patent no. 2002100745, filed 26 September 2002, and titled "Shear Head Attachment for Air Drill". However, many prior art mechanisms for harnessing power from rotational driving elements and converting it to vibrational or reciprocating 25 motion suffer from numerous disadvantages, including bulky and awkward designs, undue wear of intemal parts, frictional heating, mechanical binding between elements, and a generally non-smooth operation. There is therefore a need to overcome or alleviate the above discussed problems associated with the prior art. In particular, there is a 30 need for an improved mechanism for converting rotational motion, such as in a handheld power drill, to the vibrating or reciprocating motion of various mechanical tools.

2 OBJECT OF THE INVENTION It is an object of some embodiments of the present invention to provide consumers with improvements and advantages over the above described prior art, and/or overcome and alleviate one or more of the 5 above described disadvantages of the prior art, and/or provide a useful commercial choice. SUMMARY OF THE INVENTION According to one aspect, the present invention resides in an 10 eccentric drive mechanism, comprising: a housing; a crank shaft positioned at least partially inside the housing, the crank shaft having a first end, a second end and a central portion, the first end defining an eccentric bearing surface, the central portion defining a 15 concentric bearing surface, and the second end defining a concentric drive element; a first bearing positioned on the eccentric bearing surface; a second bearing positioned on the concentric bearing surface and engaging the housing; and 20 a pivot element having a distal end, a driving end, and a pivot axis located between the distal end and the driving end, the pivot axis being fixed relative to the housing; whereby rotation of the crank shaft causes the first bearing to orbit a central longitudinal axis of the crank shaft, causing reciprocating motion 25 of both the driving end and the distal end of the pivot element about the pivot axis. Preferably, the distal end of the pivot element comprises a cutting blade. Preferably, the distal end of the pivot element comprises a cutting 30 blade of a shearing tool.

3 Preferably, a pivot pin connects the pivot element at the pivot axis to a stationary blade of a shearing tool, the stationary blade being fixed relative to the housing. Preferably, the driving end of the pivot element comprises a fork 5 having tines positioned on opposing sides of the first bearing. Preferably, the pivot element comprises a third bearing positioned at the pivot axis. Preferably, the first and second bearings comprise ball bearings or roller bearings. 10 Preferably, the concentric drive element of the crank shaft comprises a bit for engaging a drive element of a drive tool. Preferably, the housing comprises an attachment end for attaching the housing to a drill. Preferably, the attachment end of the housing comprises a 15 clamping element for clamping the housing of the eccentric bearing mechanism to the housing of a drill. Preferably, the first end of the crank shaft is cylindrical. Preferably, a distal end of the housing provides a protective covering of the driving end of the pivot element. 20 Preferably, the eccentric bearing mechanism is made of steel. BRIEF DESCRIPTION OF THE DRAWINGS To assist in understanding the invention and to enable a person skilled in the art to put the invention into practical effect, preferred 25 embodiments of the invention are described below by way of example only with reference to the accompanying drawings, in which: FIG. I is an exploded perspective view of an eccentric drive mechanism in the form of a sheering tool, according to some embodiments of the present invention. 30 FIG. 2 is a cutaway, assembled perspective view of the shearing tool of FIG. 1, according to some embodiments of the present invention.

4 Those skilled in the art will appreciate that minor deviations from the layout of components as illustrated in the drawings will not detract from the proper functioning of the disclosed embodiments of the present invention. 5 DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention comprise an eccentric drive mechanism. Elements of the invention are illustrated in concise outline form in the drawings, showing only those specific details that are 10 necessary to the understanding of the embodiments of the present invention, but so as not to clutter the disclosure with excessive detail that will be obvious to those of ordinary skill in the art in light of the present description. In this patent specification, adjectives such as first and second, left 15 and right, front and back, top and bottom, etc., are used solely to define one element or method step from another element or method step without necessarily requiring a specific relative position or sequence that is described by the adjectives. Words such as "comprises" or "includes" are not used to define an exclusive set of elements or method steps. Rather, 20 such words merely define a minimum set of elements or method steps included in a particular embodiment of the present invention. The eccentric drive mechanism of the present invention can be used to convert rotational motion, such as the chuck or other drive element of a handheld power drill, to the reciprocating motion required of 25 various tools, such as shears, mechanical blades, and other devices. Advantages of some embodiments of the present invention include reducing undue wear of internal parts, reduced frictional heating, less mechanical binding between elements, and a generally smooth tool operation in a compact and safe design. 30 FIG. 1 is an exploded perspective view of an eccentric drive mechanism in the form of a sheering tool 100, according to some embodiments of the present invention. The tool 100 includes a housing 5 105 that substantially covers other components of the tool 100. Such components include a crank shaft 110 that is positioned at least partially inside the housing 105. The crank shaft 110 includes a first end 115, a second end 120 and a central portion 125. The first end 115 defines an 5 eccentric bearing surface 130, the central portion 125 defines a concentric bearing surface 135, and the second end 120 defines a concentric drive element 140. A first bearing 145 includes an inner race 150 and an outer race 155. The inner race 150 of the first bearing 145 is positioned on the 10 eccentric bearing surface 130. A second bearing 160 includes an inner race 165 and an outer race 170. The inner race 165 of the second bearing 160 is positioned on the concentric bearing surface 135 of the central portion 125 of the crank shaft 110. The outer race 170 of the second bearing 160 engages the housing 15 105. For example, an interior surface 175 of the housing 105 may form a compression fit around the outer race 170. A pivot element 180 includes a distal end 185, a driving end 190, and a pivot axis 195 located between the distal end 185 and the driving end 190. The pivot axis 195 is fixed relative to the housing 105. For 20 example, in the shearing tool 100, the pivot element 180 functions as a reciprocating shear blade and is attached to a stationary blade 200 by a pivot pin 205 and nut 210. The stationary blade 200 is then fixed to the housing 105 using a positioning tongue 215 in the housing 105 that resides in a positioning groove 220 of the stationary blade 200. The 25 stationary blade 200 is then bolted to the housing 105 using bolts 225. The housing 105 is then adapted to be clamped to an end of a handheld power drill using bolts 227. A third bearing 230 positioned between the pivot pin 205 and the pivot element 180 enables smooth reciprocating movement of the pivot 30 element 180 about the pivot axis 195. A cutting edge 235 of the pivot element 180 engages a cutting edge 240 of the stationary blade 200, enabling a smooth and stable shearing operation.

6 Rotation of the crank shaft 110 causes a central longitudinal axis 245 of the first bearing 145 to orbit a central longitudinal axis 250 of the crank shaft 110. That causes reciprocating motion of both the driving end 190 and the distal end 185 of the pivot element 180 about the pivot axis 5 195. In the shearing tool 100, the driving end 190 of the pivot element 180 comprises a fork having an upper tine 255 and a lower tine 260 positioned on opposing sides of the first bearing 145. Reciprocating motion of the first bearing 145 thus pushes alternately upward on the 10 upper tine 255 and downward on the lower tine 260, causing a scissors action between the cutting edges 235, 240 of the pivot element 180. Those skilled in the art will recognise that the first, second and third bearings 145, 160, 230 can comprise ball bearings, roller bearings or other alternative bearing types. 15 FIG. 2 is a cutaway, assembled perspective view of the shearing tool 100, according to some embodiments of the present invention. The concentric drive element 140 is in the form of a bit adapted to fit inside and engage a drive element (not shown) of a tool such as a spindle, hex head or a chuck of a drill. Various alternative forms of the drive element 140 20 are also useable, including for example differently shaped bits or simple holes in the crank shaft that engage a drill chuck or tool. An interior cavity of the housing 105 is adapted so that a drill drive element is spaced away from an inner wall 265, enabling the drive element of the drill to spin freely inside the housing 105. In use, an inner 25 wall 270 of the housing 105 is tightly and securely clamped to a housing (not shown) of the drill using the bolts 227, and suspends the entire shearing tool 100 in a cantilevered manner off the end of the drill. Powering the drill thus spins the drive element 140, causing eccentric motion of the first bearing 145. That causes reciprocating 30 motion of the upper tine 255 and lower tine 260 about the pivot pin 205. Because the first bearing 145 is positioned closer than the cutting edge 235 to the pivot pin 205, the cutting edge 235 obtains an increased 7 reciprocating range of travel compared to the tines 255, 260. That enables the tines 255, 260 to be safely covered by an end of the housing 105 and without impacting the interior of the housing 105 during use. As will be understood by those having ordinary skill in the art, most 5 of the moveable components of the shearing tool 100 can be fabricated of steel or steel alloys. The housing 105 typically is manufactured of metal or a high strength polymer material. Advantages of some embodiments of the present invention thus include reducing undue wear-of internal parts, reduced frictional heating, 10 less mechanical binding between elements, and a generally smooth tool operation in a compact and safe design. Alternative embodiments of the present invention also can be used to power other types of tools and devices that require the conversion of motion either from a rotating motion to a reciprocating motion or from a reciprocating motion to a rotating 15 motion. The above description of various embodiments of the present invention is provided for purposes of description to one of ordinary skill in the related art. It is not intended to be exhaustive or to limit the invention to a single disclosed embodiment. As mentioned above, numerous 20 alternatives and variations to the present invention will be apparent to those skilled in the art of the above teaching. Accordingly, while some alternative embodiments have been discussed specifically, other embodiments will be apparent or relatively easily developed by those of ordinary skill in the art. Accordingly, this patent specification is intended to 25 embrace all alternatives, modifications and variations of the present invention that have been discussed herein, and other embodiments that fall within the spirit and scope of the above described invention.

Claims (5)

1. An eccentric drive mechanism, comprising: a housing; 5 a crank shaft positioned at least partially inside the housing, the crank shaft having a first end, a second end and a central portion, the first end defining an eccentric bearing surface, the central portion defining a concentric bearing surface, and the second end defining a concentric drive element; 10 a first bearing having an inner race and an outer race, the inner race of the first bearing positioned on the eccentric bearing surface; a second bearing having an inner race and an outer race, the inner race of the second bearing positioned on the central portion of the crank shaft, the outer race of the second bearing engaging the housing; and 15 a pivot element having a distal end, a driving end, and a pivot axis located between the distal end and the driving end, the pivot axis being fixed relative to the housing; whereby rotation of the crank shaft causes the first bearing to orbit a central longitudinal axis of the crank shaft, causing reciprocating motion 20 of both the driving end and the distal end of the pivot element about the pivot axis.

2. The eccentric drive mechanism of claim 1, wherein the distal end of the pivot element comprises a cutting blade. 25

3. The eccentric drive mechanism of claim 1, wherein the distal end of the pivot element comprises a cutting blade of a shearing tool.

4. The eccentric drive mechanism of claim 1, wherein a pivot pin 30 connects the pivot element at the pivot axis to a stationary blade of a shearing tool, the stationary blade being fixed relative to the housing. 9

5. The eccentric drive mechanism of claim 1, wherein the driving end of the pivot element comprises a fork having tines positioned on opposing sides of the first bearing.