1. Technical Field
The present disclosure relates to aerial lift systems and vehicles provided with such lift systems.
2. Background Art
One type of aerial lift includes a vehicle onto which a pivotable turntable is mounted, with the turntable having a series of adjustable, and possibly, extendable booms onto which a platform or basket is mounted. Typically, a lower and an upper boom are used to position a platform or basket away from the vehicle to a desired location so that a person within the basket or platform may perform work or maintenance on an object that is otherwise difficult to access.
It is desirable for the boom to allow the basket to extend beyond the footprint of the vehicle. However, as the basket moves with respect to the vehicle, the center of mass of the vehicle system, i.e., including the boom, basket, the person or persons in the basket and whatever other cargo is in the basket, migrates. Several measures can be taken to overcome a tendency of the vehicle to tip when the boom is extended away from the vehicle.
For example, the weight and/or footprint of the vehicle are increased so that the vehicle system is more stable. However, it is undesirable to increase the weight of the vehicle because it makes transporting the vehicle to a work site that much more difficult. Also, if the surface near the work site is unstable, such as may result from a presence of sand or mud, the more that the vehicle system weighs, the more likely the vehicle will become stuck during maneuvering. Another measure used to stabilize the vehicle in the elevated position calls for increasing the track width and/or the wheel base, whereby the foot print of the vehicle is increased, which improves stability. However, the larger the footprint, the less maneuverable the vehicle becomes. Also, a wider vehicle is prevented from accessing certain locations that it may have otherwise been able to access.
Another commonly employed measure involves providing a counterweight on the turntable so that the counterweight rotates with the turntable. The counterweight balances the boom extending in a direction away from the counterweight, which is called a “forward” direction regardless of the angle of the rotation of the turntable. Thus, the forward and rearward directions are defined with respect to the turntable, not with respect to the vehicle or any object that is being accessed from the basket. However, the counterweight provides an undesirable imbalance force when the upper boom is rotated in a rearward direction. Thus, this measure commonly includes taking additional measures to prevent the boom from moving too far rearward.
In some other designs, the positions of the booms are controlled by hydraulic cylinders. By knowing the extent that the hydraulic cylinders are extended, the combinations of boom positions leading to tipping can be avoided. However, such a system relies on having sensors to measure positions of the hydraulic cylinders, a controller, and frequent calibration of the sensors to ensure sufficient measurement accuracy.
In yet another prior design, an upright member is provided between the lower and upper booms. The upright is actively controlled via hydraulic feedback to maintain it in a vertical position. A disadvantage of such a system is that it requires additional hydraulic cylinders managed by complex valving and additional sensors. Furthermore, the system may require periodic calibration. Also, by introducing an intermediate link, i.e., the upright, additional play is introduced. The amount of play is exacerbated at the operator's station in the ‘basket. Such play undermines the operator's sense of security.
To solve at least one problem in the prior art, an aerial lift system is disclosed which includes a vehicle, a turntable coupled to the vehicle, a lower boom coupled to the turntable at a first turntable pivot, a lower linear actuator coupled between the turntable and the lower boom, and a mechanical link coupled to the turntable at a second turntable pivot. The turntable is coupled to the vehicle with an axis of rotation of the turntable being substantially vertical. The upper side of the turntable includes pivot joints for at least a lower boom and a mechanical link. The axis of rotation about these first turntable and second turntable pivots, in some embodiments, is substantially perpendicular to the axis of rotation of the turntable with respect to the vehicle. A bell crank is coupled to: the lower boom at a first bell-crank pivot and to the mechanical link at a second bell-crank pivot. The system includes an upper boom coupled to the lower boom at a boom-to-boom pivot. The system also includes an upper linear actuator coupled to the bell crank at a third bell crank pivot and coupled to the upper boom. The linear actuators are any suitable linear actuator such a hydraulic cylinder. The mechanical link, in some embodiments, includes two members. The lower linear actuator passes between the two members of the mechanical link as it couples between the lower boom and the turntable.
By providing the mechanical link and the bell crank, the upper and lower booms are constrained in such a manner that they are prevented from accessing positions in which vehicle tipping may occur. This presents advantages over prior designs. For example, in one embodiment of the invention in which the lower boom is coupled to the upper boom, there are fewer pivot points than some prior art systems. Thus, there is less play in the system at the operator basket, which may extend 50 feet or more from the vehicle, during positioning of the basket or due to the wind acting upon the basket. The operator feels more secure and comfortable when the basket bounces to a lesser degree.
At least one embodiment of the invention obviates the need for complicated electronic/hydraulic control and hydraulic actuators used to limit rear instability. Furthermore, the mechanical system does not need calibration, as needed with a system using control valves and actuators. Furthermore, service intervals for some embodiments of the invention described by the present disclosure, which are mechanically based, are likely longer than service intervals for prior systems which may include sensors, controllers, and complex valving.
As shown in
In one embodiment, a proximal end of the lower hydraulic cylinder 20 extends through a slot in turntable 14 to provide stowage space for lower hydraulic cylinder 20. Lower hydraulic cylinder 20 is trunnion that is in turn mounted to the turntable in one embodiment, with the trunnion joint being located along the body of lower hydraulic cylinder 20, i.e., not connected at the proximal end of lower hydraulic cylinder 20. A mechanical link 22 is also coupled to turntable 14 via a pivot joint 23. In one embodiment, mechanical link 22 comprises two members 24 and 26. In the embodiment shown in
According to one embodiment, aerial lift 13 includes a bell crank 30 which is pivotally coupled to mechanical link 22 and lower boom 16. Bell crank 30 is also pivotally coupled to an upper hydraulic cylinder 32 at one end of the upper hydraulic cylinder with the other end of upper hydraulic cylinder 32 coupled to upper boom 28. Upper hydraulic cylinder 32 couples with upper boom 28 away from either end of upper boom 28. Upper boom 28 is coupled to lower boom 16 at a close end of upper boom 28. At a far end of upper boom 28, a basket assembly 34 is coupled. Basket assembly 34 includes a platform and/or cage in which an operator, and possibly tools and/or cargo, may be lifted. Basket assembly 34 includes pivotal links and hydraulic cylinders so that it may be raised, lowered, extended, etc. with respect to the far end of the upper boom 28. Furthermore, basket assembly 34 may include components to provide users with automated, or semi-automated, leveling to ensure that basket assembly 34 remains substantially level. In the embodiment shown in
A counterweight 38 (shown in
In the preceding paragraphs, embodiments showing some of the elements of the present invention have been described. In the succeeding discussion, the system characteristics leading to improved operation are described in regards to
In
Generally, bell crank 30 has three pivots: a lower boom pivot 30a, a mechanical link pivot 30b, and an upper hydraulic cylinder pivot 30c. As shown in
In
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In
Combinations of the extreme positions of hydraulic cylinders 20 and 32 are shown in
By adding bell crank 30 and mechanical link 22, as shown in
According to embodiments of the present disclosure, upper boom 28 and lower boom 16 are directly linked with their range of motion controlled via hydraulic cylinders, 20 and 32, mechanical link 22, and bell crank 30. In some prior art systems, an additional link is included between upper and lower booms. As each link between the turntable and the basket adds to the amount of play experienced at the basket, it is an advantage, according to some embodiments of the present disclosure, that no such additional link is employed.
Another advantage, according to the present disclosure, is that the operator can directly control hydraulic cylinders 20 and 32 without relying on an electronic controller. In some prior art systems, a controller is interposed between operator controls and linear actuators to ensure that undesirable positions of associated booms are not accessed. In other prior systems, an additional link is provided between upper and lower booms and a complex control scheme is employed to ensure that undesirable positions are not accessed.
While the best mode has been described in detail, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. For example, hydraulic cylinders 20 and 32 are shown in