Patent Application
20080152429
The present application relates generally to linear lost motion mechanisms, and, more particularly, to linear lost motion mechanisms located within a tubular handle of a machine, such as a concrete finishing machine.
Concrete finishing machines have been used for many years to level and finish large concrete pads. Such machines typically include a rotatable trowel blade assembly having a plurality (e.g., three or four) generally planar trowel blades mounted on trowel arms projecting radially outwardly from a common hub, all of which are rotated by a gasoline-powered engine. The trowel blades rest directly on the concrete surface to be finished and support the machine's entire weight.
Concrete finishing machines typically further include means for controllably pivoting the trowel blades about their respective radial axes, to change their pitch relative to the concrete surface to be finished. Changing the blades' pitch correspondingly changes the proportion of blade surface contacting the concrete surface, such that the machine's weight is supported by a larger or smaller area of the surface.
In use, a concrete finishing machine makes several passes over the concrete surface as the concrete hardens, with the blade pitch being specially selected for each pass. In the initial pass, when the concrete is still very wet and plastic, the blade pitch is usually adjusted to be substantially parallel with the concrete surface, thereby lying flat upon it and spreading the machine's weight over a maximum surface area. In subsequent passes, as the concrete hardens and becomes less plastic, the blade pitch is progressively increased, with the pitch used in the final pass sometimes being as much as about 30 degrees.
Improvements in recent concrete formulations have made some concrete slabs include pockets or areas of varying plasticity. In such situations, it can be desirable to rapidly adjust the trowel blade pitch in order to produce the desired finish. It can also be desirable to adjust the trowel blade pitch when the machine is being moved to an adjacent area where the concrete is at a different stage of hardness. In this situation, which frequently occurs when very large concrete pads are being formed, it may be desirable to adjust the blade pitch very rapidly.
In one embodiment, a trowel blade pitch adjustment system comprises a rack located within a handle tube of a concrete trowel. The rack is attached to the handle tube such that motion relative to the rack is also relative to the handle tube. The system further comprises a pitch block located within the handle tube, the pitch block comprising an aperture containing one or more pins biased onto the rack by an angled upper surface and a biasing spring, thereby frictionally locking the pitch block to the rack. The system further comprises a release located within the handle tube and configured to compress the biasing spring upon actuation, thereby releasing the frictional lock between the pitch block and the rack. The system further comprises a tension cable coupled to the pitch block and extending through the handle tube to engage with a blade rotation apparatus configured to pivotally rotate one or more blades of the concrete trowel.
In another embodiment, a trowel blade pitch adjustment system comprises a first member located within a handle tube of a concrete trowel and attached to the handle tube such that motion relative to the first member is also relative to the handle tube. The system further comprises a second member located within the handle tube and configured to selectively frictionally engage with the first member using a biasing spring, and a blade rotation apparatus in communication with the second member and configured to pivotally rotate one or more blades of the concrete trowel.
In another embodiment, a concrete finishing machine comprises a rotatable trowel blade assembly comprising a plurality of trowel blade arms projecting radially outwardly from a common hub, each arm carrying a trowel blade, and an engine coupled to the rotatable trowel blade assembly. The concrete finishing machine further comprises a tubular machine handle coupled to the rotatable trowel blade assembly and a blade pitch adjustment system comprising a linear lost motion mechanism located within the tubular machine handle.
In another embodiment, a linear lost motion mechanism is located within a tubular handle of a machine. The linear lost motion mechanism comprises a first member located within the tubular handle and configured to selectively frictionally engage with a second member using a biasing spring. The linear lost motion mechanism further comprises a release located within the tubular handle and configured to compress the biasing spring upon actuation, thereby releasing the first member from its selective frictional engagement with the second member.
These and other embodiments of the present application will be discussed more fully in the detailed description. The features, functions, and advantages can be achieved independently in various embodiments of the present application, or may be combined in yet other embodiments.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that various changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense.
The present application describes a linear lost motion mechanism located within a tubular handle of a machine. Although this mechanism is described primarily with reference to adjusting the blade pitch of a concrete finishing machine, those of ordinary skill in the art will appreciate that the linear lost motion mechanism can be used to perform numerous other functions in connection with a wide variety of machines. For example, in some embodiments, the linear lost motion mechanism can be used to control the blade depth of a concrete saw or to control a remote throttle assembly of any machine having a suitable engine.
In operation, the pitch of the trowel blades 125 relative to the concrete surface 130 on which they rest can be manually adjusted using the blade pitch adjustment system of the present application. In the illustrated embodiment, an operator actuates the blade pitch adjustment system using a pitch handle 140 pivotally secured to the tubular machine handle 135. In other embodiments, the blade pitch adjustment system can be actuated using a variety of other suitable mechanisms, such as, for example, levers, linear actuators, etc. An operator makes blade pitch adjustments based on the hardness or plasticity of the concrete surface 130, beginning with the blades 125 lying substantially flat on the surface 130 when the concrete is very wet or plastic, and ending with the blades 125 at a substantial angle (e.g., about 30 degrees) when the concrete has substantially hardened.
When an operator moves the pitch handle 140, it actuates a linear lost motion mechanism contained within the tubular machine handle 135, as described in more detail below with reference to
As illustrated in
In the exemplary embodiment shown in
Alternatively, the pitch block extension 235 may comprise a wide variety of other suitable devices configured to frictionally engage the rack 240 with a biasing spring. For example, in some embodiments, the pitch block extension 235 may comprise a pair of slotted tabs through which the rack 240 extends. The tabs may be fastened together at one end and biased apart with a biasing spring at the other end to frictionally engage the slots with the rack 240. Various other mechanisms for frictionally engaging the pitch block extension 235 with the rack 240 using a biasing spring will become apparent to those of skill in the art in view of the present disclosure.
Referring again to the embodiment illustrated in
When an operator desires to adjust the blade pitch, the operator rotates the pitch handle 140, causing the release 225 to compress the biasing spring 255 and move one of the pins 250 away from the corresponding ramp 245 in the pitch block extension 235. This movement releases the rack 240 from the pitch block extension 235, thereby allowing the pitch block 215 and the pitch block extension 235 to move relative to the rack 240 in the direction of rotation of the pitch handle 140. At the same time, a bearing 260 pushes against the pitch block 215, causing it and the pitch block extension 235 to move in the direction of rotation of the pitch handle 140.
The movement of the pitch block 215 and the pitch block extension 235 relative to the rack 240 may change the blade pitch of the concrete finishing machine 100 using a variety of suitable techniques. For example, in the illustrated embodiment, the pitch block 215 is coupled to a tension cable 265, which extends through the handle tube 205 and engages with a suitable blade rotation apparatus located on or under the gear box of the concrete finishing machine 100. In some embodiments, the concrete finishing machine 100 includes a suitable counterbalancing apparatus, such as a compressed coil spring located within the tubular machine handle 135, coaxial with the tension cable 265, to provide mechanical advantage to the operator when rotating the pitch handle 140.
When the operator releases the pitch handle 140, the release 225 ceases to exert force on the biasing spring 255, and the linear lost motion mechanism 200 returns to the “static” condition described above. In this condition, the biasing spring 255 forces the pins 250 into the ramps 245, which causes the rack 240 to become frictionally locked with the pitch block extension 235. As a result, the blade pitch remains locked in its current position when the operator releases the pitch handle 140. [0029] The trowel blade pitch adjustment system of the present application exhibits distinct advantages over conventional systems. For example, the blade pitch adjustment system described above utilizes an efficient linear lost motion mechanism, which advantageously enables operators to rapidly adjust the blade pitch of the concrete finishing machine 100 when desired. In addition, unlike many conventional systems, the blade pitch adjustment system of the present application is advantageously contained entirely within the tubular machine handle 135, thereby providing additional protection from potentially harsh environmental conditions and other wear and tear.
Although this invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art, including embodiments that do not provide all of the features and advantages set forth herein, are also within the scope of this invention. Accordingly, the scope of the present invention is defined only by reference to the appended claims and equivalents thereof.
