The first clamping part can move in relation to the second clamping part in order to clamp the object being handled by moving the first clamping part from a free position into the clamping position. Another clamping part (see description below) is provided in which a gripping part allows displacement with respect to the frame as long as the clamping force of the first clamping part on the second clamping part is below as minimum value. This allows relatively lightweight objects to be clamped in an improved way for better handling.
Fig 1 – Side view of main clamping device design with a clamping part and gripping surface, which can be displace up to a minimum load
Background
Clamping devices on which the development is based are intended for use with loading and unloading devices such a hoist and cranes for plate material and elongate objects, or for moving the same.
The invention refers to two previous patents (US-A-4,641,877 and NL-A-7414215) in which there are two clamping parts, the first being rotatably connected to a frame and connected to a movable lifting eye by means of an arm. If the object load is placed between the clamping parts, the lifting eye slides in the frame when the device is lifted so that the arm causes the first clamping part to rotate. The teeth of the first clamping part then lock onto the plate load, and the first clamping part exerts a force in the direction of the second clamping part, clamping the plate load.
For the clamping action to be sufficiently strong the object being lifted has to have a minimum weight, and in many cases when handling thin and lightweight plate material, the clamping action has been found to be insufficient in many cases. Therefore a minimum acceptable load for the clamping device will be specified as well as the work load limit (WLL). Depending on the hardness of the material to be clamped this may be 5-10% of the WLL. In the case of small clamps of the established design (WLLs of 0.5 or 1t) it may be that they cannot be used in certain cases say the applicants. For example if a steel plate load of 1mm thickness and dimensions 1x2m is to be lifted the weight force for vertical lifting is 160N. With a clamp of 0.5t WLL, the weight has to be 5% of WLL, for example, at least 250N, so the plate cannot be lifted.
Fig 2 – Side view and detail of a second embodiment with a clamping part with sliding surface under spring load
It has been found that the mechanisms of earlier patents cited (as above) are effective in the case of heavy plates but not for lifting lightweight plates. The applicants say that it is preferable, in such a situation, if the gripping surface of the first clamping part contacts the plate first whilst the surface of the second clamping part has as little friction as possible with respect to the surface of the load object plate. This allows the plate to slide slightly with respect to the first gripping surface, which may result in the teeth of the first gripping part penetrating the surface of the plate. The gripping surface of the second clamping surface will contact the plate surface if the first clamping part has sufficient grip on the plate surface, and the second clamping part exerts a specified minimum force on the plate in the direction of the second gripping surface.
The applicants already have a patent (GB-A-1,385,772) for a hoist clamp with a toggle lever system, pivotally coupled. The first lever of this system is pivotally connected to a hoisting eye by a pin movable in a slot in the slide of the clamp. A second lever is coupled to an axis fixed with respect to the side of the clamp and has a working surface eccentric with respect to the axis. The clamp also has a pressure surface on a wedge toothed on its slanted side. Coupled to the side of the clamp is another member, also with toothing and carrying a wedge slidingly mounted so that the toothed sides are directed towards each other. This wedge is spring-biased downwards. When a pressure force is applied the toothing blocks upward movement of the wedge on the member. A further lever can block the wedge in its upward position.
Fig 3 – Side view of a third embodiment with a clamping part with a pre-biased sliding part
When a load object plate is placed between the working surface and pressure surface the wedge is released using the further lever and the wedge is pressed downward, clamping the plate. The other lever, which blocks the toggle lever system, is then released. On starting to hoist the toggle levers are pulled to transfer the hoisting force to the working surface and strongly clamping the plate between the working surface and pressure surface.
A disadvantage of this design is that the clamp does not allow relatively light objects to be hoisted securely, as the clamping force still depends on the weight of the object being handled.
Description
All the embodiments of the invention are based on the same type of lifting clamp as shown in the figures. The clamping device (1) has a frame (2) in two parts in which a lifting eye (3) can move by means of a slot hole (4) and guide (5). The lifting eye is connected to an operating arm (6).
A slot (7) in the frame accommodates part of the load object to be clamped. A first clamping part (8) is connected to the frame on a rotary shaft (9), and also to the operating arm by means of rotary shaft 10. This clamping part has a gripping surface (11) positioned at a distance from rotary shaft 9, increasing as slot 7 is entered. Toothing provides a high friction surface, although any gripping surface can be used, which results in less friction in the direction into the slot than out of the slot.
Opposite the first clamping part is a second clamping part (12) also with a gripping part (13). The clamping device has a lock to keep the operating arm in position and thus lock the first clamping part.
Fig 4 – A fourth embodiment in side view with a tiltable clamping part
Operation
When at rest the lifting eye and guide can repose at the bottom of the slotted hole so that the part of the gripping surface 11 closest to rotary shaft 9 is closest to the second gripping surface, and the overall distance between them is at maximum. The free moving operating arm can cause clamping part 8 to pivot about rotary shaft 9. If a load plate is placed in slot 7, due to the increasing distance between gripping surface 11 and rotary shaft 9, the distance between the gripping surfaces is reduced until both surfaces of both clamping parts bear against the plate surfaces. As lifting takes place the force exerted by clamping part 9 on the plate increases and the teeth of gripping surface 11 penetrate the surface. Due to the weight of the plate the first clamping part 8 is subject to a force out of the slot, resulting in a force which pushes the plate against the second clamping part. Thus the teeth on the second gripping surface also penetrate the surface of the plate material.
In the first embodiment of the invention shown in Fig 1 gripping part 13 is mounted in a holder (18), which is slidable at right angles to axis ‘a’. A block of elastic material (20) is positioned below the holder, and between the holder and carrier 19 fixed to the frame. Thus the gripping part is movable under prebias. The holder is installed in the carrier via a shaft (21) slidable in slot 16. If the clamped load is smaller than the minimum, the block of elastic material will be compressed so that the gripping part moves together with the objected to be clamped to a point where the spring force compensates for the weight. When the weight is greater than the spring force the gripping part will move no longer.
Alternative embodiments
Fig 2 shows a the side view of a second embodiment with inset detail in which clamping part 12 has a carrier part with toothed rollers (35) on a shaft (31), with mounting springs (32). The rollers are partly accommodated in a cavity. When a force is greater than the spring force, the surface of the rollers but against surface 33 and will not be able to rotate about their axes.
In Fig 3 there is a sliding part in the gripping part 13, which is prebiased by means of a spring on a shaft. The sliding part, within a slot, provides a prebiased sliding surface (17), which, when at rest, protrudes beyond the gripping surface. Thus the frictional resistance or grip can be reduced to a minimum force to be exerted on the sliding surface. The sliding surface may be of Teflon, nylon, polyethylene or any suitable material, such as steel, with a low coefficient of friction. The gripping surface partially surrounds the sliding surface, which can displace from an extended position where it, to some extent, shields the gripping surface, to a retracted position where the gripping surface is prominent.
In the fourth embodiment shown in side view in Fig 4 the second clamping part (12) consists of a pivotable gripping part (50) moving about pivot 51. A compressible ring (17) on the gripping surface causes the gripping surface not to touch the surface of the object to be clamped at a minimum pressure. If the force is greater than the minimum value the gripping surface contacts the surface of the object to be clamped.
About the patent
This article is an edited version of WIPO international patent application no. WO/2008/069664, published on June 12 2008, and filed on December 7 2007 as international application number PCT/NL2007/050629. The applicants are the inventor Nicolas Cornelis Gillesse of Arnhem, the Netherlands and Inter Product BV of Celsiusstraat 51, NL-6716 BZ Ede, the Netherlands. The prior national patent is Dutch patent 2000364 of December 8 2006.
An International Search Report has been completed for this application, although it is pointed out that one claim (number 14) is wrong in relying on references to description or drawings, and the claim is too unclear for a search report to be drawn up for this claim.
Disclaimer
This article and drawings are edited versions of the patent and may omit legally or technically important details.
Marketing
For more information contact Inter Product, tel: +31 (0)318 690 999, fax: +31 (0)318 690 933, email: info@interproduct.com.
