Patent Application
20120251241
1. Field of the Invention
The invention relates generally to hand guided vibratory machines and, more particularly, relates to a vibratory machine with monolithic handle mount that reduces the transmission of vibrations to the operator. The invention additionally relates to a method of operating such a machine.
2. Discussion of the Related Art
Many hand guided machines employ vibratory action. Examples of such machine include vibratory plates or tampers for compacting soil and vibratory wet screeds for leveling and smoothing freshly poured concrete. While these various machines may differ in purpose and function, they all employ a vibratory generator to impart vibrations to a work piece such as a ground-engaging plate or shoe or a concrete-engaging blade.
One specific example of a known hand guided vibratory machine is a vibratory wet screed. The vibratory wet screed employs an elongated blade that extends over a surface of freshly poured wet concrete. A motor, mounted above the blade, activates a vibration generator, which in turn imparts a vibration through the elongated blade. An operator grasps a handle extending above the elongated blade, and pulls the vibrating elongated blade over the concrete surface while simultaneously walking backwards. As a result, the vibratory action of the blade smoothes and levels the wet concrete.
Prior to the introduction of the vibratory wet screed, the process of screeding wet concrete was a manual task. Manual wet screeding typically involved at least two laborers dragging opposite ends of an elongated piece of two-by-four lumber board over a rough surface of wet concrete. Additional laborers would shovel and rake the concrete into position ahead of the approaching screeding board, to ensure that no voids or shallow areas remained in the smooth surface of the concrete after the screeding board had passed. This manual wet screeding process is labor intensive, requiring at least two individuals positioned at opposite ends to drag the screeding board. On average, this manual process would limit a crew of six laborers to pouring and screeding a slab of 6,000 to 8,000 square feet per day. Furthermore, this manual approach is time consuming, physically fatiguing, and often results in uneven or inconsistence results, due in part to the lack of vibration imparted onto the wet concrete surface. Additionally, manual manipulation of concrete typically requires additional water to be added to the concrete mixture, as to increase the workability of the uncured concrete product. However, increasing the water component results in both prolonged curing times as well as increases the presence of voids or weaknesses within the resulting cured concrete slab.
As a result of the many disadvantages of manual wet screeding, the use of vibratory wet screed machines has become an industry standard. However, operation of vibratory wet screed machines presents drawbacks of their own. Most notably, the vibration produced by the vibration generator is not localized to the elongated blade, but rather is transmitted throughout the entire wet screed machine, including through the handle mounts to the handle. According to this undesirable vibration, an individual operating a vibratory wet screed may become fatigued after operating the vibratory wet screed for a prolonged period of time. To ensure that operators are not exposed to such fatiguing effects, regulatory and standard setting agencies in the United States, Europe, and elsewhere have issued guidelines relating to the operation of vibrating tools. These guidelines indicate that machines which impart a hand-arm vibration (HAV) value of 5.0 or greater onto the operator must comply with additional reporting requirements and operating limitations.
To reduce this undesired vibration, some vibratory wet screed machines utilize resilient mounting components between the handle mounts and the screed blade and/or at other locations in the vibrational path from the screed blade to the handles to insulate the handles from vibration. However, these resilient mounting components reduce the ability of the operator to adequately control the pitch, direction and rotation of the elongated blade. Specifically, the “give” of these elements leads to movement of the handles relative to the screed blade, resulting in a reduction in responsiveness. Furthermore, these additional components add unnecessary weight to the machine. Added weight is undesirable because it is generally preferable to make vibratory wet screeds and other hand guided machines as light as possible to reduce operator effort.
Despite these prior attempts to limit the transmission of vibrations to the handles of hand operated vibratory machines, there remains need for improvement. In light of the foregoing, a handle mount configured to reduce the transmission of vibration originating in the vibration generating component of the portable hand operated machine is desired.
One or more of the above-identified needs are met by providing an improved handle mount for use in a vibratory machine that reduces the transmission undesirable vibrations to the machine's handles. The apparatus is ideally suited for use with vibratory wet screeds, but is usable with other vibratory hand operated machines as well such as tampers and vibratory plate compactors.
In accordance with a first aspect of the invention, a handle mount is configured for mounting on a portable vibratory machine having a vibration generator that produces a vibration along an attached workpiece. The handle mount comprises a monolithic element having a partial coil located along its length. The partial coil is flanked by a lower section mounted at least indirectly to the workpiece, and an upper section at least indirectly bears a handgrip for use by the operator. The partial coil effectively acts a spring that reduces the transmission of vibrations originating at the vibration generator.
In accordance with another aspect of the invention, the monolithic handle mount may include additional curved elements, allowing the handgrips to be positioned in an ergonomically preferred location for the use of the operator.
The partial coil and any additional curved elements may further provide a protective guard protecting the side of the machine's engine. Furthermore, the additional curved elements may effectively orient the partial coil to lie in a preferred plane to maximize vibration reduction in that plane.
In accordance with yet another aspect of the invention, a method of operating a vibratory hand operated machine is provided having a vibration absorbing handle mount located between the vibration generator and the handle grips that are held by the operator.
These and other objects, advantages, and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.
A preferred exemplary embodiment of the invention is illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which:
A wide variety of handle mounts for vibrating hand operated machines could be constructed in accordance with the invention as defined by the claims. Hence, while the preferred embodiments of the invention will now be described with reference to a portable vibratory wet screed machine, it should be understood that the invention is in no way so limited. For instance, it is also usable with a variety of different portable vibratory machines that are potentially subject to undesired vibration transmission through the handle.
The engine 24 of this exemplary embodiment, as seen in
Referring especially to
As mentioned above, the engine 24 and vibration generator 26 of an illustrated embodiment are coupled to the elongated blade via a frame 28. Referring to
As previously indicated, and illustrated in
Referring to
Turning now to
The partial coil 220 includes a curvature having a radius of approximately 3.0 inches. The partial coil 220 is oriented such that it exhibits a degree of leaf spring-like flexibility while in operation, sufficient for reducing the transmission of vibrations along the handle assembly 32. The partial coil 220 simultaneously exhibits a significant degree of rigidity as to allow the static load of the machine 22 to be transmitted to the handgrips 36 without deflection and not inhibit an operator's manipulation of the machine 22. The partial coil 220 is oriented such that it lies in and effectively dampens two axes of undesired vibration, namely the vertical axis of the machine 22 and the fore-and-aft axis of the machine 22. It is also considered within the scope of the invention that the partial coil 220 additionally could be oriented to lie in a third axis of undesired vibration, namely the longitudinal axis of the machine 22. Such undesirable vibration may originate in the vibration generator 26 and/or the engine 24. The partial coil 220 of the illustrated embodiment exhibits a spring constant of approximately 0.80 kg/mm along the fore-and-aft axis of the machine 22, 0.76 kg/mm along the longitudinal axis of the machine 22, and 0.40 kg/mm along the vertical axis of the machine 22. The partial coil 220 of the illustrated embodiment exhibits an arc length maximized to suppress undesirable vibration without sacrificing maneuvering control. That arc length is 149.8 mm at the centerline of the monolithic handle 214, in the illustrated embodiment, but could vary significantly, such as between 75 and 250 mm. That arc angle is 112.3 degrees in the illustrated embodiment, but could vary significantly, such as between 75 and 200 degrees. Accordingly, the illustrated embodiment of the partial coil 220 will sufficiently suppress vibrations oriented in the along a vertical axis and a fore-and-aft axis of the machine 22, without imparting significant reduction on operator 40 steering torque. This reduction in undesirable vibrations will result in diminished occurrence of fatigue experienced by an operator 40. The intermediate curved segments 222, 224 may, if desired, also have a radius of approximately 3.0 inches, hence facilitating fabrication by permitting the use of the same bending tool to form all curved sections. However, the arc length of the additional curved segments 222, 224 can be much less than that of the partial coil 220, as see in
It should be noted that the partial coil 220 and intermediate curved segments 222, 224 of the handle mount 206 also serve as a guard that extends along the sides of the engine 24, thereby preventing damage to the engine 24 if the screed machine 22 were to fall or be placed on its side when not in operation. Also, the intermediate curved segment 222 located between the partial coil 220 and the upper section 216 may direct the handle mount 206 upwards, to provide an ergonomic orientation of the handle 208 and handgrips 36, for engagement by the operator 40.
In operation, an operator 40 starts the engine 24, and engagement of the clutch causes the drive shaft to rotate. Manipulating the throttle actuation lever 114 adjusts the operating speed of the engine drive shaft, which ranges from 4,000 to 8,000 rpm, and more preferably 6,000 to 7,000 rpm in standard operating conditions. The rotation of the drive shaft causes the input shaft 110 of the vibration generator 26 to rotate. The input shaft 110 then rotates the imbalance located within the vibration generator 26 to produce vibrations. The vibrations are transmitted to elongated blade 30 and propagate through the blade 30 in a generally sinusoidal pattern. These vibrations typically have a magnitude of about 9-13 HAV at standard engine operating speeds of, e.g., 6,500 rpm. Some of these vibrations are transmitted to the mounting plate 124 through the support bracket 118 and thence to the lower section 34 of the handle assembly 32, i.e. the lower section 218 of the lower handle mounts 206. However, a substantial portion of those vibrations are damped by the partial coils 220 in the lower handle mounts 206. The magnitude of the vibrations induced by the vibration generator 26 are proportional to the speed at which the engine 24 drive shaft rotates. In addition to generating increased vibrations in the vibration generator 26, an engine 24 running at high speed may also form significant vibration that will be distributed throughout the vibratory wet screed 22. Specifically, an engine 24 operating at a speed greater than 6,000 rpm may impart a vibration of between 2.0 and 3.0 HAV into the mounting plate 124 and thus to the lower ends of the lower section 218 of the lower handle mounts 206. Accordingly, at optimal operating speed, the partial coil 220 of the handle mounts 206 may suppress vibrations originating in the engine 24, as well as those vibrations originating in the vibration generator 26.
Tests have confirmed that that partial coil 220 of each lower handle mount 206 is capable of significantly reducing the transmission of vibrations transmitted to the lower handle mount 206 by the vibration generator 26 and the engine 24. In fact, assuming an input vibration at the lower section 218 of the lower handle mounts 206 of 14 HAV, tests have shown that the vibrations at the upper section 216 of the lower handle mounts 206 are reduced to less than 10 HAV. In fact, those vibrations are reduced to less than 7 HAV and even less than 5 HAV. In these tests, the engine 24 was operated at a series of operational speeds. At these specified operational speeds, hand-arm vibration (HAV) values were measured first at the location of the lower section 34 of the handle assembly 32, i.e. the lower section 218 of the lower handle mount 206. A second set of HAV values was measured at the location of the handgrips 36, i.e. upper section of the handle 208. The operational speed of the engine 24 was recording in rotations per minute (rpm) and the hand-arm vibration value was measure in units of meters per second squared (m/ŝ2). The results of this test are reflected in tabular form in Table 1 and graphically in
The previous test was then repeated while utilizing a vibratory wet screed comprising relatively straight lower handle mounts, lacking a partial coil, as is known in the prior art. Specifically, the handle had essentially the shape of the handle illustrated in U.S. Pat. No. 7,175,365. The results of this test are reflected in tabular form in Table 2 and graphically in
As indicated in Table 1 and by the lines 306 in
Further tests have confirmed that that partial coil 220 of each lower handle mount 206 is capable of significantly reducing the transmission of vibrations transmitted to the lower handle mount 206 by the vibration generator 26 and the engine 24, while exhibiting decreased deflection in response to operator 40 applied force. In this test, the handle assembly 32 according to the illustrated embodiment of the present invention was fastened to a fixed location at the mounting bracket 210. The height of the handle 208 of the right handle subassembly 200R was then measured to establish a baseline value. In order to simulate the twist motion of an operator trying to maneuver only one side of the blade, weight of 30 lbs. (13.61 kg) was then suspended from the right hand grip of the handle 208, and a deflection distance of 17.0 mm was measured in the handle assembly 32, along the fore-and-aft axis of the machine 22. The test was then repeated with the handle assembly 32 repositioned to measure deflection about the vertical and horizontal axis of the machine 22. The results of these tests are reflected below in Table 3. According to the measurements obtained, the spring constant values of the handle assembly 32, including a partial coil 220, in accordance with the present invention were calculated for each axis of the machine 22. These spring constant values are similarly presented in Table 3.
The test was then performed while utilizing the handle assembly of a vibratory wet screed comprising relatively straight lower handle mounts, lacking a partial coil, as is known in the prior art. Specifically, the handle assembly had essentially the shape of the handle illustrated in U.S. Pat. No. 7,175,365. After being fastened to a fixed location, the height of the handle was measured to establish a baseline value. A weight of 30 lbs. (13.61 kg) was then suspended from the handgrip of the right handle subassembly, and a deflection distance of 27.0 mm was measured in the handle, along the fore-and-aft axis of the machine.
The test was then repeated with the handle assembly repositioned to measure deflection about the vertical and horizontal axis of the machine. The results of these tests are reflected below in Table 4. According to the measurements obtained, the spring constant values of the handle assembly, comprising relatively straight lower handle mounts, lacking a partial coil, as is known in the prior art were calculated for each axis of the machine. These spring constant values are similarly presented in Table 4.
Resultantly, this test demonstrates that the handle assembly 32 of the present invention, incorporating a partial coil 220, exhibits a 37.0 percent decrease in deflection in the direction of operator pull, i.e. fore-and-aft axis of the machine 22, as compared to relatively straight lower handle mounts, lacking a partial coil, as is known in the prior art. This decreased deflection along the fore-and-aft axis is consistent with the greater fore-and-aft axis spring constant exhibited in the present invention. In operation, the diminished deflection in the direction of operator pull is realized through improved maneuverability of the machine 22, according to the present invention. Moreover, the handle assembly 32 of the present invention exhibits a lower spring constant along both the longitudinal and vertical axis of the machine 22, as compared to the relatively straight lower handle mounts, lacking a partial coil.
Many changes and modifications could be made to the invention without departing from the spirit thereof. For instance, the handle assembly may be composed entirely of the monolithic handle, or may alternatively the monolithic handle may be combined with additional handle assembly components. The invention is also applicable to vibratory rammers, portable plate compactors, pneumatic vibrators and other similar portable vibratory hand operated machines, which would benefit from reduction in undesirable vibration transmission through a handle as provided in the current invention. The scope of other changes and modifications will become apparent from the appended claims.
