GB2379434A

GB2379434A - A vibration absorber for a lift truck

Info

Publication number: GB2379434A
Application number: GB0121799A
Authority: GB
Inventors: Keith Francis Messer
Original assignee: Lansing Linde Ltd
Current assignee: Linde Material Handling UK Ltd
Priority date: 2001-09-10
Filing date: 2001-09-10
Publication date: 2003-03-12
Anticipated expiration: 2021-09-10
Also published as: GB0121799D0; GB2379434B; DE10240851A1

Abstract

A lift truck comprises a lifting frame 3 on which a load carrying attachment 5 is secured in a manner that allows it to move vertically and a compensating device 7 is arranged on an upper portion of the lifting frame 3. The compensating device 7 reduces the bending vibrations of the lifting frame 3 in direction 6 and comprises at least one mass element 8, which can be moved relative to the lifting frame 3 in a direction that has a horizontal component and may also comprise damping elements or springs. The compensating device 7 is embodied in such a way that a natural frequency of a vibration of the mass element 8 corresponds to a resonant frequency of the bending vibration of the lifting frame 3.

Description

Industrial truck with a lifting frame The invention relates to an industrial truck with a rafting frame on which a load carrying attachment is secured in a manner that allows it to move vertically and which is mounted by means of a lower portion on a frame of the industrial truck.

The invention also relates to a lifting frame for mounting to the frame of an industrial truck.

Industrial trucks of this type are, for example, front-end fork-lift trucks, fork-tif reach trucks or high-tiff trucks. According to a very simple embodiment, the lifting frame is connected rigidly to the frame of the industrial truck. In the case of front-end forklift trucks and fork-lift reach trucks, the fitting frame is generally capable of tilting about a horizontal axis. In the case of fork-lift reach trucks, the lifting frame can additionally be displaced in a horizontal direction relative to the frame.

A load carrying attachment can be moved up and down on the lifting frame, which is often embodied as a telescopic lifting frame with a vertical mast that cannot be raised and at least one extendable mast, which can be extended along the vertical mast The load carrying attachment is generally embodied as a load fork.

One known problem with all industrial trucks of the type described above is that the lifting frame can vibrate, an elastic bending vibration about the fixed bearing arising at the bottom of the vertical mast A distinct vibrational motion in the longitudinal direction of the industrial truck can be detected in this case at the upper end of the lifting frame.

Under certain boundary conditions, if the truck travels over bumps at a certain speed, for example, the vibration of the lifting frame can increase to such an extent due to resonant effects that the comfort of the operator and the operating safety of the industrial truck are impaired.

An object on which the invention is based is therefore to make available an industrial truck in which the occurrence of resonant vibrations of the tilting frame is prevented or reduced.

According to the invention there is provided an industrial truck with a lifting frame on which a load carrying attachment is secured in a manner that allows it to move vertically and which is mounted by means of a lower portion on a frame of the industrial truck. A compensating device for bending vibrations of the lifting frame is arranged on an upper

portion of the lifting frame, the compensating device comprising at least one mass element, which can be moved relative to the lifting frame in a direction that has a horizontal component. The arrangement of the compensating device at the upper end of the lifting frame is particularly effective since the deflection of the lifting frame due to the vibration is greatest at this point. During movement of the mass element relative to the lifting frame, the lifting frame is acted upon by reaction forces. These reaction forces counteract the vibration of the lifting frame.

The arrangement is particularly simple if the compensating device is embodied in such a way that movement of the mass element is caused by a vibrational motion of the lifting frame. The compensating device is thus a passive arrangement for which no active actuators or control device is required.

The mass element is secured movably on the lifting frame by means of a bearing element. The bearing element allows relative motion between the lifting frame and the mass element. The bearing element furthermore defines the degrees of freedom of the mass element and hence the possible direction of motion relative to the lifting frame.

According to a particularly advantageous refinement, the bearing element is embodied as a radial bearing, preferably as a radial sliding-contact bearing. The mass element can thus perform a rotary motion about the axis of the radial bearing relative to the lifting frame. In this arrangement, the axis of the radial bearing extends essentially transversely to the longitudinal direction of the industrial truck, which also corresponds to the main direction of travel of the industrial truck.

In another refinement, the bearing element is embodied as a linear bearing, preferably as a linear sliding-contact bearing. The linear bearing extends essentially horizontally in the longitudinal direction of the industrial truck.

According to a particularly expedient refinement of the invention, at least one spring element is provided, which is connected to the lifting frame, on the one hand, and to the mass element, on the other hand.

Here, the spring element is arranged in such a way that, during a deflection of the mass element relative to the lifting frame, it exerts on the mass element a force that

counteracts the deflection. The spring element thus exerts a restoring force on the mass element that rises as a function of the severity of the deflection of the mass element. This also allows a vibrational motion of the mass element.

According to another refinement of the invention, at least one damping element is provided in addition to the spring element or instead of the spring element. The damping element exerts a counterforce on the mass element in a direction opposite to the current direction of motion of the mass element The mass element is preferably embodied as a pendulum, the gravitational force on the mass element exerting a force that counteracts deflection during a deflection of the pendulum from the vertical.

In order, in particular, to prevent the occurrence of resonant vibrations of the lifting frame, the compensating device is embodied in such a way that a natural frequency of a vibration of the mass element corresponds to a resonant frequency of the bending vibration of the lifting frame. In the case of resonance, the mass element then vibrates out of phase with the vibration of the lifting frame and, in the process, continuously produces a counterforce opposed to the vibration of the lifting frame.

If the lifting frame has at least one vertical mast, which is connected to the frame of the industrial truck, and at least one extendable mast, which can be raised relative to the vertical mast, the compensating device is arranged on an upper portion of the vertical mast. To travel relatively large distances, the extendable mast is generally retracted, the upper end of the vertical mast thus also representing the upper end of the lifting frame. The compensating device according to the invention suppresses vibrations of the vertical mast, in particular. The compensating device can also be fitted to the top of the extendable mast to reduce the mast movement during the stacking or retrieval of loads.

The invention also provides a lifting frame for mounting to the frame of an industrial truck, the lifting frame being of the kind defined above.

Further advantages and details of the invention are explained in greater detail by means of the exemplary embodiments illustrated in the schematic figures, in which Figure 1 shows an industrial truck according to the invention,

Figure 2 shows the compensating device of the industrial truck according to the invention, Figure 3 shows the compensating device in accordance with Fig. 2 with the lifting frame elastically deflected, Figure 4 shows another embodiment of a compensating device according to the invention, and Figure 5 shows another embodiment of a compensating device.

Figure 1 shows an industrial truck according to the invention embodied as a fork-lift reach truck. The fork-lift reach truck has a driver's position 1 with a driver's seat oriented transversely to the main direction of travel 2. In other embodiments, the invention is applicable to any trucks comprising a lifting frame, e. g. counterbalanced forklift trucks or order picking trucks. In front of the driver's position 1 there is a lifting frame 3, which can be displaced along a frame 4 of the fork-lift reach truck relative to the driver's position 1. The lifting frame 3 comprises two spaced lifting posts, one of which conceals the other in the illustration in Fig. 1. Each lifting post comprises a vertical mast not capable of vertical movement and an extendable mast, which can be extended upwards along the vertical mast A load carrying attachment 5 embodied as a fork is guided in a vertically adjustable manner on the extendable mast.

While the industrial truck is being driven in the main direction of travel 2, vibration of the lifting frame 3 in direction 6 occurs, especially if the track is uneven, and the lifting frame 3 bends elastically. To prevent such vibration of the lifting frame 3, a compensating device 7 comprising a mass element 8 and two springs 9, 10 is, according to the invention, arranged at the upper end of the vertical mast of the lifting frame 3.

Figure 2 shows the compensating device 7 in accordance with Fig. 1 in a schematic illustration. The mass element 8 is mounted in pendulum-fashion on the lifting frame 3 by means of a radial bearing 12 via a connecting rod 11. Two upper supports 13,14 for the spring elements 9,10 are connected rigidly to the mass element 8 by crosspieces 15,16. On the other hand, two lower supports 17,18 of the spring elements 9,10 are

situated on the lifting frame 3. When the mass element 8 vibrates relative to the lifting frame 3 about the radial bearing 12, the spring elements 9,10 are thus forcibly shortened or lengthened.

Figure 3 shows an instantaneous illustration of the compensating device during a vibrational motion of the lifting frame 3. Here, the upper region of the lifting frame 3 is tilted to the right by the angle a and is instantaneously moving further in direction 20.

(The vibrations of the lifting frame that actually occur in practice result in significantly smaller tilt angles.) The mass element 8 vibrates out of phase with the lifting frame 3 and, at the instant illustrated, is moving relative to the lifting frame 3 in direction 21. As a result, the mass element 8 exerts a reaction force F on the lifting frame 3 via the radial bearing 12. This reaction force counteracts the deflection of the lifting frame 3 and hence its vibrational motion. In order to optimize the action of the compensating device 7, the natural frequency of the mass element 8 is set to the resonant frequency of the lifting frame 3 by appropriate selection of the spring elements 9,10 and the length of the connecting rod 11.

Figure 4 shows another embodiment of the invention, in which a mass element 30 can be displaced along a rod 31 by means of a linear bearing, the rod 31 being aligned essentially parallel to the main direction of travel 2 (Fig. 1) of the industrial truck. During a deflection of the mass element 30, spring elements 33,34 are stressed via an intermediate piece 32 and thus exert a restoring force on the mass element 30. The intermediate piece 32 is connected to the springs in an articulated manner, while it is connected to the mass element 30 by means of an articulated elongate hole that allows length compensation.

Figure 5 shows another embodiment of the invention, in which a mass element 40 can likewise be displaced along a rod 41 by means of a linear bearing, the rod 41 being aligned essentially parallel to the main direction of travel 2 (Fig. 1) of the industrial truck. In this arrangement, spring elements 43,44 are arranged coaxially with the rod on both sides of the mass element 40 and thus produce a restoring force that acts directly between the mass element 40 and the lifting frame 3.

Claims

Claims :

1. An industrial truck with a lifting frame, on which a load carrying attachment is secured in a manner that allows it to move vertically and which is mounted by means of a lower portion on a frame of the industrial truck, wherein a compensating device for bending vibrations of the lifting frame is arranged on an upper portion of the lifting frame, the compensating device comprising at least one mass element, which can be moved relative to the lifting frame in a direction that has a horizontal component.

2. An industrial truck according to Claim 1, wherein the compensating device is embodied in such a way that movement of the mass element is caused by a vibrational motion of the lifting frame.

3. An indüstrial trück according to Claim 1 or Claim 2,, -a, herein the mass element is secured movably on the lifting frame by means of a bearing element.

4. An industrial truck according to Claim 3, wherein the bearing element is embodied as a radial bearing.

5. An industrial truck according to Claim 4, wherein the radial bearing is a radial sliding contact bearing.

6. An industrial truck according to Claim 3, wherein the bearing element is embodied as a linear bearing.

7. An industrial truck according to Claim 6, wherein the linear bearing is a linear sliding-contact bearing.

8. An industrial truck according to any one of Claims 1 to 7, including at least one spring element connected to the lifting frame, on the one hand, and to the mass element, on the other hand.

9. An industrial truck according to Claim 8, wherein the spring element is arranged in such a way that, during a deflection of the mass element relative to the lifting frame, it exerts on the mass element a force that counteracts the deflection.

10. An industrial truck according to Claim 8 or 9, wherein at least one damping

element is provided in addition to the spring element or instead of the spring element.

11. An industrial truck according to any one of Claims 1 to 10, wherein the mass element is embodied as a pendulum, the gravitational force on the mass element exerting a force that counteracts deflection during a deflection of the pendulum from the vertical.

12. An industrial truck according to any one of Claims 1 to 11, wherein the compensating device is embodied in such a way that a natural frequency of a vibration of the mass element corresponds to a resonant frequency of the bending vibration of the lifting frame.

13. An industrial truck according to any one of Claims 1 to 12, wherein the lifting frame has at least one vertical mast, which is connected to the frame of the industrial truck, and at least one extendable mast, which can be raised relative to the vertical mast, the compensating device being arranged on an upper portion of the vertical mast.

14. A lifting frame for mounting to the frame of an industrial truck, the lifting frame being of the kind defined in any one of the preceding claims.

15. An industrial truck substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

16. A lifting frame for an industrial truck substantially as hereinbefore described with reference to and as shown in the accompanying drawings.