CLAIM OF PRIORITY

[0001] This application claims priority to U.S. Provisional Application Serial No. 61/781,336 entitled "Rotary Impact System for a Power Tool" by Eli Share, filed March, 14, 2013, the disclosure of which is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] This disclosure relates generally to power tools, and, more particularly, to impacting power tools.

BACKGROUND

[0003] Impact hammer devices are portable power tools that are commonly used to drive nails into a receiving medium such as wood or drywall. Impact hammers typically include an actuator that rotates an output shaft. A transmission converts the rotational motion of the actuator output shaft into reciprocating linear movement of a striking mechanism. The striking mechanism typically extends into a magnetized sleeve. A nail is placed in the sleeve and held therein by the magnetic force in the magnetized sleeve. The nail is then pressed against the receiving medium and the impact hammer is activated. Each reciprocating strike of the striking mechanism advances the nail further into the receiving medium until the nail is fully inserted in the receiving medium.

[0004] In some instances, the transmission is unable to generate sufficient force to move the striking mechanism. The power tool then stalls, and cannot generate the impact force necessary to drive the nail into the receiving medium. Some impact hammers include a groove in an output shaft of the transmission to enable the impacting portion of the transmission to avoid the striking mechanism as the output shaft rotates in a stall condition. These systems, however, require precise machining to groove the shaft, and installation of the systems is cumbersome. Improved transmission systems for impact hammers are therefore needed.

SUMMARY

[0005] In one embodiment, a rotary impact system provides improved recovery from a stall condition. The rotary impact system comprises a striking rod, a first member, a second member, a first drive member, and a biasing member. The first member includes a first radially extending impact projection, and a first axial side portion including one of a first guide and a first holder. The first member is axially movable by a first distance between a first position whereat the impact projection is axially aligned with the striking rod and a second position whereat the impact projection is not axially aligned with the striking rod. The second member includes a second axial side portion configured to receive motive force from a motor and a third axial side portion in opposition to the first axial side portion and including the other of the first guide and the first holder. The first axial side portion and the third axial side portion define a system incline, and the system incline defines an axial distance equal to the first distance. The first drive member is partially received within both the first guide and the first holder, and the first drive member movable along a length of the guide while remaining partially received within the first holder as the first member moves from the first position to the second position. The biasing member is configured to bias the first member toward the first position.

[0006] In another embodiment, a rotary impact system comprises a striking rod, a gear, an impact member, a first drive member, and a biasing member. The gear includes a gear shaft, a first geared side, and a second side opposite the first side. The second side includes at least one first axially inclined surface having one of a first groove and a first indentation. The impact member is rotationally supported by the gear shaft and includes an impact projection and a third side with at least one second axially inclined surface in opposition to the at least one first axially inclined surface and having the other of the first groove and the first indentation. The impact member is axially movable along the gear shaft from a first position whereat the impact projection is axially aligned with the striking rod to a second position whereat the impact member is not axially aligned with the striking rod. The first drive member is partially received within both the first groove and the first indentation, and the biasing member is configured to bias the first member toward the first position.

[0007] In yet another embodiment, a method of operating a rotary tool enables improved recovery from a stall condition. The method comprises biasing a first member toward a first position whereat an impact projection of the first member is axially aligned with a striking rod, transferring rotational force from a second member to the first member through at least one drive member while the first member and the second member are in a first rotational orientation with respect to each other, rotating the impact projection into contact with the striking rod using the transferred rotational force, and stopping rotation of the first member with the striking rod. The method further includes continuing to rotate the second member after the rotation of the first member has been stopped thereby moving the first member and the second member out of the first rotational orientation, forcing the first member to move axially away from the second member using at least one inclined surface and the at least one drive member by the continued rotation of the second member, moving the impact projection out of axial alignment with the striking rod by the axial movement of the first member, and rotating the first member back into the first rotational orientation while axially moving the first member to the first position after moving the impact projection out of axial alignment with the striking rod.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a cross-sectional schematic view of a conventional impact hammer.

[0009] FIG. 2 is an exploded top perspective view of a rotary impact system.

[0010] FIG. 3 is an exploded side perspective view of the rotary impact system of FIG. 1

[0011] FIG. 4 is a side view of the rotary impact system of FIG. 1.

[0012] FIG. 5 is a front view of the rotary impact system of FIG. 1.

DETAILED DESCRIPTION

[0013] For the purposes of promoting an understanding of the principles of the embodiments described herein, reference is now made to the drawings and descriptions in the following written specification. No limitation to the scope of the subject matter is intended by the references. This disclosure also includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the described embodiments as would normally occur to one skilled in the art to which this document pertains.

[0014] FIG. 1 is a cross-sectional schematic view of a conventional impact hammer 10. The impact hammer 10 includes a tool housing 14, a motor 18, a transmission housing 22, a striker 26, and a retractable sleeve 30. The motor 18 includes an output shaft 20 that rotates in response to activation of the motor 18 in the impact hammer 10. A transmission device (not shown) located within the transmission housing 22 converts the rotational motion of the output shaft 20 into a reciprocating striking motion of the striker 26. As the impact hammer 10 is used, the retractable sleeve 30 is forced into the transmission housing 22 to enable the striker 26 to move closer to a receiving medium.

[0015] FIG. 2 depicts an exploded view of a rotary impact system 100 for an impact hammer, such as impact hammer 10. The impact system 100 is positioned within a transmission housing, such as transmission housing 22 of the impact hammer 10 of FIG. 1. The impact system 100 includes a bevel gear 104, three spherical drive members 108, an impact anvil 112, a bushing 116, a spring 120, a first bearing 124 and a second bearing 128.

[0016] The bevel gear 104 includes an outwardly extending portion 130 on which a geared region 132 is located, a drive shaft or gear shaft 136, and three gear incline surfaces 140 on an axial side of the outwardly extending portion 130, each gear incline surface 140 having a respective cam groove 142 (FIG. 3). The cam grooves 142 each have a first groove end 143 and a second groove end 144, and the cam grooves 142 are configured to accommodate the spherical drive members 108 such that the spherical drive members 108 are only movable

circumferentially with respect to the bevel gear 104 between the first and second groove ends 143 and 144. The gear shaft 136 has a first shaft end 145 (FIG. 2) and a second shaft end 146, and defines a longitudinal axis 147 of the impact system 100. In the illustrated embodiment, the system includes three spherical drive members, three gear incline surfaces, and three cam grooves. In other embodiments, however, the system includes a different number of spherical drive members, gear incline surfaces, and cam grooves.

[0017] The impact anvil 112 includes three anvil incline surfaces 148 in an axial side, each having a respective concave spherical indentation 152, and two impact lugs 156. The impact anvil 112 further defines a central opening 162 (FIG. 3) extending centrally through the impact anvil 112. Each spherical indentation 152 is configured to accommodate one of the spherical drive members 108 in a fixed position relative to the impact anvil 112. The anvil incline surfaces 148 are configured to rest against the gear incline surfaces 140. The impact lugs 156 project radially outwardly from the body of the impact anvil 112, and have an impact surface 158 configured to strike a striking rod 160 (FIGS. 4 and 5) as the impact anvil 112 rotates. The striking rod 160 is connected to a tool holder (not shown), which, in one embodiment, holds a nail to be driven into a surface by reciprocating movement of the striking rod and tool holder. In the illustrated embodiment, the impact anvil 112 includes two impact lugs 156, though the impact anvil has a different number of impact lugs in alternative embodiments.

[0018] In the illustrated embodiment, the bevel gear 108 and the impact anvil 112 each include inclined surfaces 140 and 148, respectively. The combined incline of the surfaces 140 and 148 defines a system incline, which is at least equal to the distance required to move the impact lugs 156 out of alignment with the striking rod 160. In some embodiments, only one of the bevel gear and the impact anvil has inclined surfaces, while in other embodiments the bevel gear and impact anvil have inclined surfaces that have different angles with respect to one another. As described herein, the impact lugs and striking rod are considered to be "axially aligned" with one another when the impact lugs are capable of contacting the striking rod as the impact anvil rotates, while the impact lugs and striking rod are considered to be "not axially aligned" when the impact lugs and the striking rod are not capable of contacting one another.

[0019] The bushing 116 extends through the central opening 162 of the impact anvil 112, around the gear shaft 136, to facilitate independent rotation of the impact anvil 112 with respect to the gear shaft 136. The spring 120 is interposed between the second bearing 128 and the impact anvil 112 to urge the impact anvil 112 toward the bevel gear 104 and press the spherical drive members 108 securely between the spherical indentations 152 and the cam grooves 142. The second bearing 128 supports the second end 146 of the gear shaft 136, while the first bearing 124 supports the first end 145 of the gear shaft 136. The bearings 124 and 128 are configured to retain the gear shaft 136 and the components supported thereon in a fixed relative position, while enabling the gear shaft 136 to rotate relative to the bearings 124 and 128.

[0020] In operation, an actuator (not shown), for example an electric motor, rotates a gear (not shown) meshing with the geared portion 132 of the bevel gear 104 to rotate the bevel gear 104 in direction 200 about the central axis 147 of the gear shaft 136 (FIGS. 2 and 3). As the bevel gear 104 and gear shaft 136 rotate, the spherical drive members 108 rotate with the bevel gear 104 at the first end 143 of the cam grooves 142, transferring the rotational force of the bevel gear 104 to the impact anvil 112, which rotates in response to the rotation of the bevel gear 104. As the impact anvil 112 rotates, one of the impact lugs 156 strikes the striking rod 160, imparting energy on the tool holder (not shown) and the tool or nail held therein. Repeated contact of the impact lugs 156 and the striking rod 160 generates a reciprocating motion of the striking rod 160, producing the impact force acting on the tool holder that drives the nail into the receiving medium.

[0021] In some instances, the rotational velocity of the impact anvil 112 is insufficient to enable the impact lug 156 to move the striking rod 160. When the impact lug 156 is unable to move the striking rod 160, the impact anvil 112 remains in a fixed rotational position with the impact lug 156 abutting the striking rod 160. The bevel gear 104 and gear shaft 136 continue to rotate in direction 200 in response to continued activation of the actuator such that the cam grooves 142 rotate with respect to the spherical drive members 108. Since the cam grooves 142 are in the gear incline surfaces 140, the rotation of the impact anvil 112 with respect to the bevel gear 104 results in the spherical drive members 108 moving from the first groove end 143 toward the second groove end 144, which urges the spherical drive members 108 axially in direction 204 (FIG. 5) along the incline. Movement of the spherical drive members 108 pushes the impact anvil 112 along the longitudinal axis 147 in direction 204 away from the bevel gear 104, counter to the force of the spring 120.

[0022] As the impact anvil 112 continues to move in direction 204, the impact lug 156 eventually reaches a point at which the impact lug 156 axially clears the striking rod 160. Once the impact lug 156 releases from the striking rod 160, the force stored by the spring 120 pushes the impact anvil 112 against the spherical drive members 108, moving the spherical drive members 108 within the cam grooves 142 back to the first groove end 143 and rotating the impact anvil 112 faster than the bevel gear 104 until the impact anvil 112 returns to the initial position relative to the bevel gear 104 and the impact lug 156 is once again axially aligned with the striking rod 160.

[0023] The reader should appreciate that, in other embodiments, the rotary impact system described herein is configured to rotate in both rotational directions to impact the striking rod and generate an impact force in more than one direction by using an impact lug having a hump shape instead of a single incline. Additionally, while the drive members and the indentations in the impact anvil are described herein as spherical, the reader should appreciate that in other embodiments the drive members have another desired shape, for example an oval shape or a cylindrical shape. Further, while the rotary impact system has been described for use in an impact hammer, the reader should appreciate that, in other embodiments, the rotary impact system is used in different impact devices, such as impact wrenches, rotary hammers, and impact drivers. [0024] It will be appreciated that variants of the above-described and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives,

modifications, variations or improvements may be subsequently made by those skilled in the art that are also intended to be encompassed by the disclosure.