The present invention generally relates to elevators and, more particularly, is concerned with elevators with a scissor lift mechanism.
In various work platform lift machines, such as scissors lifts, elevated platforms, cranes, etc., hydraulic cylinders are used to provide the necessary lifting forces. The hydraulic cylinders are typically part of a hydraulic actuation system for operating the lift mechanism to raise and lower the work platform. The scissors lift mechanism includes a plurality of pairs of arms pivotally interconnected in a scissor-like fashion so as to raise and lower as the arms pivot between generally vertical unstacked and horizontal stacked orientations relative to one another. The hydraulic actuation system generally employs an even number of hydraulic cylinders for causing pivoting of the pairs of arms to expand the lift mechanism. Typically, the hydraulic cylinders are interconnected between an adjacent set of the arms.
An example of a lift machine with two symmetrically arranged hydraulic actuation systems is described in the U.S. Pat. No. 5,375,681, which belongs to the same family as the German patent application DE 42 25 871-A1. Each of the two hydraulic actuation systems provides for the up and down movement of one of two scissor columns, which together carry a car. Two vertical guiding means are provided which are symmetrically arranged with respect to the scissor columns of the lift machine. The guiding means are rather complicated and the actuation of the two hydraulic actuation systems has to be synchronized.
The German patent applications DE 42 34 490-A1 and DE 43 13 068-A1 disclose various lift machines with an even number of synchronized hydraulic actuation systems. There are two vertical scissor columns, each of which is lifted by a corresponding one of said hydraulic actuation systems. The lowermost ends of the arms of the scissors are guided above ground (cf.
The use of hydraulic actuation systems and positioning of the hydraulic cylinders in lift machines have several disadvantages. One major disadvantage is that hydraulic actuation systems tend to leak hydraulic fluid which is a substance toxic to the environment and therefore requires a considerable amount of care and attention and must be contained and disposed of properly. Another significant disadvantage of hydraulic actuation systems is that they are not very efficient, typically operating at levels up to approximately fifty percent efficiency. Thus, lift machines that are hydraulically powered not only invite high maintenance and/or repair costs, but also tend to consume quite some power.
Yet another important disadvantage is that using hydraulic cylinders within the scissors arm stack to raise the lift mechanism not only causes machine instability due to high centers of gravity, but also such hydraulic cylinders tend to be squishy and jerky in operation and thus hydraulic actuation systems lack smooth and precise control of the movement of the lift mechanism to raise and lower the working platform. The design rules of work platforms with scissor assembly cannot be easily applied to elevators for carrying passengers, since an elevator for passengers usually has to move faster and smoother and has to reach the respective landing levels more precisely. Furthermore, the comfort is an issue.
It is yet another disadvantage that in many scissor systems two scissor columns are used in parallel and concurrently in order to provide the required stability. In such scissor systems, typically two hydraulic cylinders are employed which have to be synchronized in order to provide for a concurrent movement of the two scissor assemblies, as mentioned in connection with the above patents and patent applications.
There are scissor lift mechanisms, such as scissor jacks for lifting vehicles, that are manually actuated. An example of a scissor jack with a double-lead ACME threaded screw shaft is disclosed in the U.S. Pat. No. 6,527,251, for example. The ACME mechanism provides for a self-locking function.
Some scissor lift mechanisms comprise an electro-mechanical screw drive instead of hydraulic cylinders. An example of a work platform with a scissor lift mechanism and telescopable electro-mechanical screw drive is disclosed in the U.S. Pat. No. 6,044,927. The screw drive comprises a non-threaded extension tube in a telescopable support relationship with a threaded ballscrew shaft. The screw drive extends between two pivotally movable arms of the scissor assembly. The ballscrew shaft undergoes a pivotal movement, which is a disadvantage of this mechanism.
Another scissor lift mechanism comprising an electromechanical screw drive is disclosed in the U.S. Pat. No. 4,451,945. This patent concerns a medical couch with a central electromechanical screw drive. The screw drive is pivotally connected to a lower frame and performs a tilting movement as the couch is lifted or lowered. That is, the drive pivots about a horizontal axis. The connection between the drive and the lower frame, as well as the coupling of a nut moving up and down as the shaft rotates, are mechanically complicated. In one of the embodiments disclosed in this patent, the nut is a ball nut.
A further scissor lift mechanism comprising an electromechanical screw drive is disclosed in the U.S. Patent application with publication number US 2002/0029930-A1. Disclosed is a lift mechanism with drive having a horizontally arranged ballscrew shaft. A rotation of this shaft moves one end of a lower arm of a scissor assembly in a horizontal direction. This horizontal movement causes the scissor assembly to fold or unfold. Since the ballscrew shaft is horizontally arranged, the drive must provide high force levels in order to unfold the scissor lift mechanism in the vertical direction, in particular on the condition that the scissor lift mechanism is almost unfolded (i.e. if a load carried by the lift mechanism is held on a height which is close to the lowest possible level). This is disadvantageous.
All these mechanisms and systems have certain disadvantages, as briefly addressed. In particular the actuation is still an issue that provides further room for improvements and new concepts.
Consequently, a need exists for a different approach to actuation of the scissors lift mechanism of such lift machines which will overcome the above-mentioned disadvantages without introducing other disadvantages in their place.
The present invention concerns a scissor lift elevator assembly having the following advantages:
The above advantages do not necessarily apply to all the different embodiments, since the embodiments are implementations of the invention with a focus on optimizing particular aspects. At the same time, however, other aspects might be less perfect.
The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which:
In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following escription, it is to be understood that such terms as “horizontal”, “vertical”, “left”, “right”, “upwards”, “downwards”, and the like are words of convenience and are not to be onstrued as limiting terms.
Referring to the drawings and particularly to
In
Each pair of arms of the scissor assembly 13 comprises two longitudinal arms 17.x wherein “x” represents consecutive odd and even integers. The lower most pair of arms comprises the two arms 17.1, 17.2, for example. The arms 17.x may have a solid or hollow tubular construction and they may have a substantially rectangular, circular, triangular or oval cross-section. Though the arms 17.x may have any other suitable configuration. A length LA of each arm 17.x is smaller than a respective length (side-to-side distance) LE of the elevator car 12 if the scissor assembly 13 is to stay within a projection 12.1 of the elevator car 12. In this case, a length (side-to-side) LH and a width (front-to-back) WH of an optional hoistway 20 is only slightly larger than the length LE and a width (front-to-back) WE of the elevator car 12. It is, however, also possible to employ arms 17.x having a length LA that is greater than the length LE of the elevator car 12.
Each arm, e.g. the arm 17.3, has a pair of opposite ends 17A, 17B, as illustrated in
The elevator car 12 is of any suitable type such as the one shown in
The drive 14 is connected to the lowest cross element 16, which connects the lowest pairs of arms 17.1 and 17.2 of the scissor columns. The drive 14 is arranged such that, by activating the drive 14, a force acting on said cross element 16 in the vertical direction can be applied. Thus, the drive 14 is adapted to mechanically interact with both scissor columns for applying a force in the vertical direction for moving said cross-element 16 up or down and, thus, for folding and/or unfolding the scissor assembly 13.
Preferably, the electromechanical drive 14 is connected with a middle section of said cross element 16. This is advantageous in view of the mechanical stability of the elevator 10 since the force generated by the drive 14 acts symmetrically on the scissor assembly 13 in the same direction in which the elevator car 12 is moved.
The electromechanical drive 14 may be replaced by any drive providing an equivalent function.
Due to the fact that a scissor assembly 13 is employed, a small upwards movement of the lower most arms 17.1, 17.2 caused by the drive 14 is translated into a larger movement of the elevator car 12. The maximum movement of the drive 14 corresponds to the maximum expansion of the overall scissor assembly 13.
According to another preferred embodiment of the present invention, an electro-mechanical screw drive 26 is employed, as depicted in
There are two basic designs of the screw drive 26, both of which can be used in connection with the present invention. Basically, the corresponding threads of the screw and the nut are engaged in such a way that, by rotating the nut with respect to the longitudinal axis of the screw or by rotating the screw around its longitudinal axis with respect to the nut, a linear motion of the screw with respect to the nut can be induced. The screw is arranged such, that it projects in a hollow space of the shaft 21. In one design of the screw drive 26, the nut is fixed at the shaft 21 and the screw is rotatable by means of the electric motor 22. In the other design of the screw drive 26, the screw is fixed at the shaft 21 and the nut is rotatable by means of the electric motor 22. By activating the electric motor 22, the shaft 21 may be linearly moved with respect to the electric motor 22 and the housing 25 in a longitudinal direction 21.1 of the shaft 21 by means of the screw and the nut. By reversing the angular direction of the rotation of the nut with respect to the longitudinal direction of the screw, the direction of the movement of the shaft 21 with respect to the electric motor 22 may be reversed.
The electric motor 22 may be an A.C. or a D.C. motor.
In the embodiment in accordance with
Preferably, the electric motor 22 is arranged adjacent to the shaft 21. The overall length of the drive 26 is thus mainly defined by a shaft length LL. If the motor 22 would be arranged above or below the shaft 21, the overall length would be larger. With the motor 22 arranged at the side of the shaft 21, elevators can be realized that require less space below the lowest landing level.
Thus, by activating the electric motor 22, a linear movement of the electric motor 22 and the sliding element 23 in the vertical direction with respect to the mounting platform 11 can be induced. This linear movement forces the scissor assembly 13 to unfold and the elevator car 12 to move upwards, or the other way around.
The drive 26, as illustrated in
In an alternative approach, the way the drive 26 interacts with the scissor assembly 13 can be modified. The electric motor 22 could be fixed with respect to the mounting platform 11 and the shaft 21 could be arranged in such a way that it is linearly movable in the vertical direction with respect to the electric motor 22 and that is adapted to mechanically interact with both scissor columns for applying a force in the vertical direction for unfolding the scissor assembly. For example, the shaft 21 could be fixed at the cross element 16.
Some of the embodiments described and claimed are designed such that the downward movement of the elevator car 12 occurs without having to actively drive the shaft in a second direction. The weight of the elevator car 12 and the load on or in the car 12 contribute to a force pulling the entire arrangement downwards. If the entire arrangement is balanced appropriately, the downward force is introduced via the engagement of the corresponding threads of the nut and the screw. Depending on the actual design of the nut and the screw, the force may be sufficient to cause a movement of the shaft 21 in a second direction with respect to the electric motor 22. Due to this movement, the sliding element 23 moves downwards. The elevator car 12 and the whole scissor assembly 13 follows this down movement.
The upper end 13.1 of the scissor assembly 13 pivotally mounts the elevator car 12, as depicted in
In
Another embodiment of an elevator scissor lift according to the present invention is illustrated in
In addition or alternatively, damping elements acting on the lower ends of the arms may be employed in an elevator or elevator assembly according to the present invention. For example, the enlarged portion of the spring member 35.5 can be a terminal buffer for damping a downward movement of the scissor assembly.
According to another embodiment, the electromechanical drive 26 is an ACME screw drive or a similar kind of screw drive with a high strength screw shaft and a nut made of bronze or a synthetic material. It is advantageous to use a high efficiency reinforced self-guided ACME nut. Well suited is a nut comprising a reinforced, lubricated resin material for higher strength, higher efficiency and greater thread accuracy. The ACME thread of the shaft mates with the ACME thread of the nut. It is an advantage of the “ACME embodiment” that the scissor assembly and the elevator car will not move downwards after the drive is switched off or after the drive failed. The friction between the special nut and the screw shaft is large enough to prevent the whole system from moving downwards. It is a further advantage of the ACME screw drive or a similar kind of screw drive that no separate brake(s) are required, since the movement of the nut with respect to the screw shaft is not reversible unless the motor drives the screw or the nut. Thus, the elevator cannot fall down, even in the absence of a safety gear or a safety brake. A load-holding brake is not required either for the same reason. It is a disadvantage, however, that the efficiency of a drive using an ACME screw may be somewhat reduced.
The embodiment with the ACME screw drive exhibits an operational advantage that derives from the physical characteristics which are unique to the ACME screw thread, namely the ability for the ACME screw to become self-locking when the elevator is subjected to loads. Where loading is above a given level, the frictional forces developed among the thread lands or roots of the threaded shaft and the nut become sufficiently large to prevent the vertically downward directed force from causing the screw shaft to unwind and prematurely allow the elevator to descend in an uncontrolled manner. It is required that a minimum load is exceeded before the ACME self-locking phenomenon takes effect.
In yet another embodiment, a ball screw drive with an externally threaded ballscrew shaft and an internally threaded nut, or a caged ball screw drive, or a planetary roller screw drive may be employed. These known kinds of screw drives are the equivalent of the drives 14 and 26 and are characterized by relatively low frictions which has the advantage that a smaller electrical drive can be employed for causing a movement of the elevator car. It is, however, a disadvantage, that a separate brake is required to stop the elevator car at a desired landing level and to control downwards oriented movements of the elevator car.
The mounting platform may be used to define the shape and size of the hoistway. As depicted in
The elevator car may comprise similar guiding means, with or without spring members, than the ones situated on the ground or mounting platform. The elevator car may be a platform with some kind of edge or balustrade, or it may be a cabin with or without sliding doors, for example.
In the
Embodiments are conceivable where fewer guiding means are employed. The guiding means may be realized in many different ways, as long as at least one of the lowermost arms of the scissor assembly is horizontally guided. The same is the case for the uppermost arms. At least one of the uppermost arms is to be horizontally guided. It is, however, a disadvantage of the embodiments with fewer guiding means, that this leads to a disturbance of the symmetry of the overall assembly.
The guiding means at the lower end of the scissor assembly may be designed with a main focus on the aspect of horizontal guidance. In this case, most of weight of the elevator car, the load and the weight of the scissor assembly—herein referred to as total weight—is to be carried by the central drive. The shaft and/or the screw and/or the nut of the screw drive have to be designed accordingly. In another embodiment, the guiding means may be designed with a focus on the aspect of horizontal guiding and the mounting of the scissor assembly plus elevator car. In this case, the central drive would have to carry a smaller part of the total weight.
An elevator according to the present invention may comprise a gear box or the like for drivingly connecting the electric motor to the screw shaft or nut. In
Due to the fact that the central drive provides for a vertical guidance of the cross element or the scissor assembly, and due to the fact that at least one cross element is used to connect the two scissor columns, a very stable and rigid elevator is obtained. The elevator, according to the present invention does not require any guiding elements—such as guiding rails—for controlling movements of the elevator car in a hoistway in the vertical direction. It is even possible to install the inventive elevator without any hoistway.
Symmetry is a crucial issue. In particular when being operated, it is important to ensure that the two scissor columns move concurrently. According to the present invention this is achieved by employing a central drive that applies forces to the scissor assembly only at a central portion in order to ensure that the whole system is balanced.
Due to this it is ensured that the elevator car is kept generally always horizontal. The elevator according to the present invention is in itself stable.
In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.
Number | Date | Country | Kind |
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03405631.7 | Sep 2003 | EP | regional |