Load balancing device for a lifting application with an article to be lowered or raised

Abstract

The invention relates to a load-compensating device for a lifting application with an object to be lifted or lowered, comprising a movable platform, wherein the platform carries the object and, for the purpose of load compensation, the platform is supported by at least one spring element (5). The spring element (5) acts on a spreading unit (4, 6, 7) which, in order to achieve spreading, transfers a spring force of the spring element (5) into a scissors arrangement (3), wherein, by virtue of the scissors arrangement, the spring force results in a lifting force that produces a lifting action on the platform, and wherein a substantially constant lifting force is provided over a substantial lifting distance of the platform by the lifting geometry formed by means of the spreading unit (4, 6, 7) and the scissors arrangement (3). The size and the linearity or constancy of the supporting force (lifting force) can be set in a simple manner by adapting the geometry, in particular the length / size of the structural elements of the spreading unit and the length of the legs of the scissors arrangement. The load-compensating device is also characterized by compact dimensions, flexible handling and high performance in combination with little manufacturing, assembly and maintenance effort.

Description

[0001] The invention relates to a load balancing device for hoists and similar applications according to the preamble of patent claim 1.

[0002] The invention relates to a mechanically acting load balancing device for increasing the performance and efficiency of vertical lifting applications. This device is intended to be flexibly integrated into existing or newly designed lifting systems, thereby reducing the load on the drive train or the entire lifting mechanism and thus significantly increasing the efficiency of the overall system. This reduction in load not only reduces drive power and energy consumption, but also allows the entire lifting device to be made smaller and lighter, increases the load-bearing capacity, and thus increases the power density of the overall system.

[0003] The publication US 2011 / 0240409 A1 - Bacon "SCISSOR LIFT ASSEMBLY" shows a lifting table with scissor kinematics, in which a motor-driven spindle is arranged between two legs of a pair of scissors, whereby the lifting table has a low overall height when lowered.

[0004] The publication US 5,833,198 A - Graetz "MECHANICALLY OPERATED LIFT TABLE" also shows a lifting table with scissor kinematics, in which a spring element is arranged between the legs of a pair of scissors, wherein the spring characteristic is selected such that the lifting table, when subjected to a load package, lowers essentially by the overall height of the load package, resulting in an essentially load-independent overall height of the loaded lifting table.

[0005] Publication JP H07 267594 A - Mizouchi Seiji "MOTOR-DRIVEN TABLE LIFTER" shows a scissor lift table in which a compression spring is provided above a drive spindle to assist the drive. JP H07 267594 A discloses the preamble of claim 1.

[0006] Until now, for example, in lifting devices, as described in DE 10 2012 020 264 B4, compression spring elements were placed between the lower frame and upper frame or lifting platform in order to relieve the load on the lifting gear and the drive train. This direct connection has a number of disadvantages. For example, massive guide elements and complex spring bearings are required to prevent the compression spring elements from buckling. If lateral forces act on the spring elements, this would significantly reduce their service life. In order to ensure significant relief of the lifting gear even in the upper position, a high spring preload must be applied to the spring elements due to the flat spring characteristic curve. However, during maintenance work on the lifting system, the energy stored in the spring preload must be safely separated, decoupled or enclosed from the lifting system. This results in complex maintenance concepts and, where appropriate,additional devices.

[0007] Furthermore, the disadvantage of a direct integration of the spring elements is that a constant force curve cannot be generated over the entire stroke, since the spring force increases when moving together according to the spring characteristic curve.

[0008] Solutions with counterweights, such as those used in passenger lifts, provide constant support across the entire lifting height, but are usually not mobile and have high moving masses, making them unsuitable for many industrial applications.

[0009] It is therefore an object of the present invention to propose a load balancing device for a lifting application (lifting application, hoist, lifting / lowering conveyor, lifting table, or the like) that provides a support force that is as linear and as constant as possible over a lifting height. The required solution should be lightweight and safe to maintain after moving to a maintenance position.

[0010] The solution to this problem involves the interaction of mechanically acting spring elements with a scissor mechanism actuated by a spreading unit, which in turn supports a load-handling device, hereinafter referred to as the "platform." The solution according to the invention thus features a combination of mechanically acting spring elements with a scissor mechanism actuated by a spreading unit, which generates a uniform lifting force distribution between two platforms movable vertically relative to each other. This load balancing device is characterized by compact dimensions, flexible handling, and high performance with low manufacturing, assembly, and maintenance costs.

[0011] The object is achieved in particular by the device of patent claim 1. This proposes a load balancing device for a lifting application with an object to be lifted or lowered, comprising a movable platform, wherein the platform carries the object, and wherein the platform is supported by at least one spring element for load balancing. The spring element acts on a spreading unit, which directs a spring force of the spring element into a scissors arrangement for spreading, wherein the scissors arrangement causes the spring force to act as a resulting lifting force on the platform, and wherein the lifting geometry formed by means of the spreading unit and the scissors arrangement provides an essentially constant lifting force over a substantial lifting distance of the platform.By adjusting the geometry, particularly the length / size of the structural elements of the spreader unit and the length of the legs of the scissor assembly, the magnitude and linearity or constancy of the support force (lifting force) can be easily adjusted. The load balancing device is also characterized by compact dimensions, flexible handling, and high performance with low manufacturing, assembly, and maintenance costs.

[0012] According to the invention, the spring element (5) is designed as at least two parallel acting tension springs and preloaded with such a high spring preload that the spring element (5) is moved together to a block in an upper stroke position, so that in the event of maintenance, no additional measures for force or energy separation of the energy storage device have to be taken.

[0013] Advantageous embodiments of the invention are set forth in the dependent patent claims. Their features and advantages can be realized both individually and in combination, as needed.

[0014] The stroke geometry is advantageously designed in such a way that a changing spring force during the stroke is essentially compensated by a changing lever effect. This results in essentially constant support, thus optimized load balancing, even with steep spring characteristics, and in many cases makes a high spring preload obsolete for using the spring in a working range that is as linear as possible.

[0015] In a structurally simple embodiment, the spreading unit comprises push rods, wherein the push rods are each articulated between the spring accumulator and a scissor arm of the scissor arrangement.

[0016] The spreading unit advantageously acts on a curved geometry, whereby the curved geometry determines the course of the lever action of the spreading unit on the scissor assembly. This allows nonlinear spring force progressions to be compensated; moreover, it is possible to create a variable support force during the stroke, which is desired in some applications, by means of a corresponding design of the curved geometry. In a structurally simple and compact variant, the curved geometry is formed by at least one curved surface of a scissor arm of the scissor assembly, whereby the spring force of the spreading unit acts on the curved surface via a sliding piece or a roller construction.

[0017] In one variant, the expansion unit has an expanding wedge geometry on at least one side. This allows for a particularly compact design. Furthermore, even flat spring characteristics can be easily converted into constant load balancing or a constant support force. Depending on the application, it may be useful to provide an expanding wedge arrangement at one end of the tension spring and push rods at the other end of the spring. A combination of a curved geometry with push rods or an expanding wedge arrangement is also possible.

[0018] If the load balancing device is appropriately dimensioned, it can also perform a vertical guiding function; the supported lifting gear can then be designed with a simpler structure and be limited to the lifting function.

[0019] Embodiments of the load balancing device and advantageous embodiments are described below with reference to the drawings.

[0020] Showing: Figure 1 shows two embodiments A1, A2 of the gear kinematics of the load balancing device not according to the invention with push rods as a spreading device in a schematic representation, Figures 2 - 3 show further embodiments B, C of the gear kinematics of the load balancing device not according to the invention with alternative spreading devices in a schematic representation, Figures 4 - 5 show further embodiments D, E of the gear kinematics of the load balancing device according to the invention with alternative spreading devices in a schematic representation, Figure 6 shows a technical implementation of the variant A1 not according to the invention with a vertical guide function in the lowered (lower) and extended (upper) position, Figure 7 shows a technical implementation of the variant D according to the invention with a vertical guide function in the lowered (lower) and extended (upper) position,Figure 8 shows a technical implementation of variant D according to the invention without vertical guide function in lowered (lower) and extended (upper) positions, Figure 9 shows a technical implementation of an integration of variant D according to the invention into an existing lifting-lowering conveyor device, Figure 10 shows a technical implementation of variant D according to the invention as a lifting table with electric cylinder double motor drive in lowered (lower) and extended (upper) positions, and Figure 11 shows a technical implementation of variant A1 not according to the invention as a lifting table with push chain double motor drive in lowered (lower) and extended (upper) positions.

[0021] The Figure 1shows schematically on the left two design variants A1, A2 of the gear kinematics of the device with gear elements and on the right the corresponding force-stroke curve. The figure shows two centrally connected, mutually pivoting scissor arms (3), to each of which two pivoting push rods (4) are connected, with the opposite side of the push rods being coaxially mounted. For this purpose, a spring energy accumulator (5) acting on tension is connected, also coaxially mounted. The movable platform, with which the weight of the object to be moved is introduced into the arrangement, is not shown in the schematic representations for reasons of clarity. Figures 1 - 5 not shown.

[0022] The tensile force emanating from the energy storage device (spring arrangement) spreads the scissor arms (3) apart via the push rods (4). Consequently, the compensating force (F) acts at the ends of the scissor arms.

[0023] If a linear, vertical guide function can be dispensed with due to application requirements, the floating bearing guides (2) of variant A1 can be omitted, which in turn results in space and cost advantages. This design is shown schematically in the lower half of the Figure 1 shown using variant A2.

[0024] It is also possible to attach a lifting curve geometry (7) (short: lifting curve or curve geometry) to the scissor arms (3) on the fixed or floating bearing side instead of the push rods, in order to achieve an expansion of the scissors (3) by means of an expansion shaft running along the lifting curve; such variants D and E are shown in the Figures 4 and 5 shown. Note: In the following, the reference symbol (3) is used both for the scissor mechanism (short: scissors) and for an individual scissor arm.

[0025] The Figures 2 , 3 and 5Show variants B, C, and E. These solutions each incorporate expanding wedge technology in various combinations and are particularly suitable for spring actuators with flat characteristic curves, such as those found in commercially available tension springs or, advantageously, oval wire tension springs. By adjusting the stroke curve geometry (variants D and E), the force-stroke curve can also be optimally adjusted.

[0026] The selected ratios of scissor arm and thrust strut lengths in conjunction with the position of the pivot axes and the spring characteristic, as well as the characteristics of the stroke curves, allow the force-stroke curve of the device to be influenced. The schematically illustrated force-stroke curve in Figure 1It can be seen that a nearly constant lifting force can be achieved. If the actual force curve is compared with an ideal constant force curve, linearity deviations of less than ±1% are technically feasible. A linearity deviation of ±15% is considered the upper limit in terms of the cost-benefit ratio.

[0027] As already described for variant A2, the floating bearing guide shown in variants B, C, D, and E can also be omitted if a linear, vertical guide function is not required for specific applications, or if the lifting platform already has a vertical guide. This is often the case when existing lifting devices are retrofitted with a load balancing device.

[0028] The following describes the technical implementation options for the variants from Figure 1 and variant D from Figure 4and application examples are shown; variants B, C and E show variations in other combinations of spreading agents.

[0029] The Figure 6 shows a technical implementation of design variant A1. This illustrates the interaction of the mechanism's gear elements. The spring accumulator integrated into the lifting mechanism consists of a spring assembly composed of two compression springs mounted one inside the other. These are mechanically integrated between the thrust struts in such a way that the spring accumulator unit acts like a tension spring. The use of solid compression springs allows for a particularly high power density.

[0030] The Figure 7 shows a first technical version of variant D ( Figure 4) with a linear, vertical guide function of the load balancing device according to the invention. Four parallel-acting high-performance oval wire tension springs serve as the spring accumulator. Compared to round wire tension springs, they have a higher power density, higher spring preloads, and lower spring rates. The number of springs can increase or decrease the compensation load; coupling means (not shown) can also be provided for this purpose in order to be able to react to different loads during operation. In the example shown, the stroke curve is part of the scissor arm contour, with the expansion shaft being guided axially by means of a centrally installed shaft.

[0031] The Figure 8 shows a technical version of variant D ( Figure 4) without guide function with 4 parallel acting oval wire tension springs as energy storage. In this version, the guide on the floating bearing side has been omitted, thus eliminating the linear, vertical guide function. The guidance of the expansion shaft along the centrally installed lifting curve is advantageously achieved by means of a profile roller. An increase in the compensation force is achieved by adding pairs of spring elements. It is therefore also technically possible to Figure 8 The design shown can be operated with, for example, just two or with six or eight parallel tension springs. The high spring preload wound into the oval wire tension springs allows the desired compensation force to be generated without the need for additional preloading of the springs. Since the tension springs are compressed to a block in the upper stroke position, no additional measures are required to isolate the force or energy from the energy storage device during maintenance.

[0032] The Figure 9 shows the integration of two parallel load balancing devices from Fig.5 into an existing lifting and lowering conveyor. This lifting and lowering conveyor is used to convey a body-in-white in automotive series production. In industry, there is often a desire to increase the performance of existing systems. In this example, by integrating version D from Figure 4 This partially relieves the load on the hoist and drive train, and partly increases the load-bearing capacity of the device (in this case by 40%). Since this retrofitting involves relatively little effort and eliminates the need for a costly complete conversion of the lifting and lowering device to higher load capacities, it results in significant economic advantages.

[0033] Another application area for load balancing devices is lifting applications used on automated guided vehicles (AGVs). Here, the aspects of energy savings and increased performance are particularly important, as energy provision and supply are associated with considerable effort, and in most cases, lifting capacity is the limiting factor in this regard.

[0034] At the Figure 10 The load balancing device shown for an AGV has both a vertical guidance and drive function integrated, which enables it to be used as a lifting table.

[0035] The Figure 11The load balancing device with guide and drive function shown can be used as a lifting table for high loads up to 3 t on automated guided vehicles. The drive function is provided by two electrically synchronized push chain drives, and the vertical guidance and load balancing function is provided by two centrally installed load balancing devices made of Figure 6 realized.

Claims

1. Load balancing device for a lifting application with an article to be raised or lowered, with a moveable platform, wherein the platform bears the article, wherein for load balancing purposes the platform is supported by at least one spring element (5), wherein the spring element (5) acts on a spreader unit (4, 6, 7), which transmits a spring force of the spring element (5) for spreading into a scissor arrangement (3), wherein by means of the scissor arrangement the spring force as a resulting lifting force acts in a lifting manner on the platform and wherein by means of the lifting geometry formed by means of the spreading unit (4, 6, 7) and the scissor arrangement (3), an essentially constant lifting force is given by way of a key lifting section of the platform, characterised in that the spring element (5) is configured as at least two tension springs which act in parallel and is pretensioned with a high spring pre-load of this type such that in a top lifting position the spring element (5) is in a maximum compression state.

2. Load balancing device according to claim 1, characterised in that the spreading unit (4, 6, 7) comprises thrust arms (4), wherein the thrust arms (4) are each hinged between the spring element (5) and a scissor arm of the scissor arrangement (3).

3. Load balancing device according to claim 1 or 2, characterised in that the spreading unit (4, 6, 7) acts on a curve geometry (7), wherein the curve geometry (7) predetermines the course of the lifting effect of the spreading unit (4, 6 7) on the scissor arrangement (3).

4. Load balancing device according to claim 3, characterised in that the curve geometry (7) is formed by at least one curved surface of a scissor arm of the scissor arrangement (3), wherein the spring force acts on the curved surface by way of the spreader unit (4, 6, 7) by means of a sliding piece or a roller design.

5. Load balancing device according to one of the preceding claims, characterised in that the spreader unit (4, 6, 7) has a spreader wedge geometry at least on one side.

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