The biased load is balanced to decrease the overall weight of the system, and an equal distribution unit is installed between the hoist frame and guide rail for absorbing impact loads transferred to the hoist frame. This equally distributes the entire vertical load.

Even if a relatively heavy object is transferred there is no buckling of the girder so long as first and second support wheels included in the development are located in the first vertical surface of the girder.

Concept and earlier design

This development is for a hoist for a low-headroom crane in which it is possible to prevent an impact load incurred by the hoist frame during load shifting from being transferred to a load support roller. A biased load is balanced to allow the hoist to operate on the girder in a stable manner, allowing the hoist weight to be decreased and hoisting capacity increased.

The patent application describes the construction and operation of conventional overhead cranes including a model for a low headroom space. Duck-Rae Cho & KG Inc. already hold a patent (number 10-2006-6576) for a low-headroom crane where the installation height of the hoist and the installation height of the running girder are overlapped to minimise the installation height.

In this case the girder has an octagonal cross section with a horizontal contact surface at the upper centre of the girder, and vertical surfaces at both sides of the girder joined to the upper surface by slant surfaces. The weight of the object being lifted is supported on the upper contact surface. The full construction of this type of low-headroom overhead crane and hoist is described in the new patent application.

However, Cho’s original design has the following problems. As the weight of the lifted object is concentrated at the upper centre of the girder, the girder may be buckled, it is claimed. The load point is positioned at the centre portion of the main girder, which supports the load support wheel as the hoist frame is mounted on the girder.

The hoist frame, which positions the load point, is at the centre of the girder, causing it to buckle under certain circumstances. The upper centre of the girder, on which the load point is applied and hoist mounted, is supported by the two slant surfaces. These in turn are supported by vertical surfaces so that the load is applied through the slant surfaces. When loads are applied at a slant angle, the vertical plate bears a larger load and may be buckled.

Another problem occurs when the object load is moved and may swing from the hoist hook. This swing load is transferred to the hoist frame via the wire rope, and the impact load transferred to the hoist frame and directly to the load support wheel. The latter causes the load support roller to contact the girder in a discontinuous manner so that the driving force from the cross-running motor is prevented from being applied to the girder on which the roller should run, decreasing the driving efficiency of the hoist and causing non-uniform transfer speed.

Thirdly, the elements of the hoist frame form a cubic pipe shape or a hollow rectangular pipe shape. Thus the entire size and weight of the hoist is increased as each element has to be larger, and consequently the hoisting capacity decreases.

Lastly, the previous design has a pair of front upper support wheels at the front frames to support the stability of the hoist frame on the girder, whilst two front lower support wheels are installed at the lower side of the front frame. There are also two rear support wheels at a pair of the rear frames, totalling six support wheels. These all decrease the productivity of the hoist. In this case, as the impact load transferred to the hoist frame is also transferred to the support wheels, the life of each support wheel is shortened.

Objectives

Thus the invention of this application aims at providing a hoist for a low-space crane able to prevent an impact load from being transferred from the hoist frame to the load support wheel, which can run along a guide rail in a stable manner. An additional aim is to decrease the entire loads of the hoist frame.

Also, with the present invention, a load of large weight does not buckle the girder. First and second load support wheels are positioned on a vertical surface of the crane cross girder. Even when an impact load is applied to the hoist frame by a swinging object being transferred, it is properly absorbed and offset by an equal distribution member. The driving efficiency of the hoist is enhanced by the properly distributed weight, and the hoist is not derailed from the guide rail. The small size and weight of the hoist frame also enhance efficiency. The hoist is supported in a stable configuration at three points by support wheels – the minimum number.

Best mode

The hoist comprises hoist frames (Fig 1 – 71 and Fig 4 – 151) arranged so that the load point (P) transferred to the girders (60 and 160) is positioned at a vertical surface of one side of each girder, balancing the biased load, so decreasing the entire load. An equal distribution unit (90) is installed between the hoist frames and absorbs the impact load to the hoist frames, equally distributing the whole vertical load. For the load point P to operate at one vertical surface of the girder (60) it is preferred that the girder has a hollow rectangular shape to satisfy the operating conditions.

Construction

The main girder consists of two angle girders (61 and 62) fixed by welding to each other to form a hollow cuboid to support the hoist. A guide rail (54) is longitudinally installed on the first vertical surface (61b) of the girder. The first load support wheel (93), and the second (96) are mounted on the guide rail. Compared to the octagonal girder of the original design, the fabrication process is decreased by half. The load at point P when hoisting an object is transferred vertically throughout the vertical section 61b so that the area to support the load is maximised.

Consequently even a heavier object does not buckle the girder. The positioning of P depends on the installation of the hoist frame 71, with the equal distribution unit installed between the hoist frame and guide rail thereby absorbing any impact load and equally distributing the vertical load.

The hoist frame comprises support plates (72 and 73) with engaging grooves (72a and 73a) on the lower side. A drum cover (74) is connected to the support plates and surrounds the wire-rope drum. A plate (75) connects the other ends of the support plates. A rear support wheel (130) is supported at the rear side of the main girder. Two reinforcing brackets (76 and 77) are fixed to both sides of the above support plates, with two front support wheel (110 and 120) supported at the front side of the girder. The lower ends are opposite the front lower side of the main girder.

The winding motor (83), wire-rope drum (81), decelerator (84) and brake (85) are integral with the support plates. The three support wheels can also be provided integrated into the hoist frame, which is formed as a small, light and simple structure using the support plates to reduce weight and size, with the decreased weight increasing hoisting capacity.

The winding motor operates the wire rope (81) of the hoist, controlled by the decelerator and brake. A hook (86) is provided at the lower en of the rope, consisting of a sheave (88) connected to the rope, a sheave cover (87), and the hook itself (89) connected with the sheave.

The equal distribution unit (90) is stated as a key element of the invention and comprises support pins (91 and 92) fixed at the lower sides of the support plates, and support wheels 93 and 96 mounted on the guide-rail with roll-contact as the support pins are mounted.

The support pins include support parts (91a and 92a) with slots (91b and 92b) in the lower edges of the main support plates. Spherical contact parts (91c and 92c) are formed at the lower sides of the support parts 91a and 92a.

As shown in Figs 1 and 2, the wheels 93 and 96 have insertion grooves (94c and 97c) so that the support plates are located at their centres. Their bodies 94 and 97 have spherical grooves (94d and 97d) so that the contacts parts (91c and 92c) of the support pins roll-contact with the lower sides of the insertion grooves. Load support rollers 95 and 98 are engaged with the bodies and mounted on the guide rail along which they run.

Sidewalls (94a and 97a) are formed at the insertion grooves (94c and 97c) of the bodies, with engaging holes (94b and 97b) formed in them. Support bolts (99 and 100) are inserted through these engaging holes and supported by the main plates. Constant intervals are so maintained between the first and second insertion grooves and the first and second support plates.

The cross running motor (Fig 3 – 80) is connected with the first load support roller (95) of the first load support wheel (93) to drive the hoist along the guide rail. The motor could also be installed at the second support (96).

By focus-applying the load-point P to the girder vertical surface 61b instead of to the centre of the horizontal surface of the girder, as in conventional forms, buckling of the girder is prevented.

Impact load transfer

The patent application describes the impact swing load transfer mechanism in great detail. Firstly the swing load transfers from the hoist wire rope to support plates via the wire-rope drum, and the impact load goes to the support pins 91 and 92, causing them to swing so that rolling contact occurs between through the mechanism described above including the contacts parts 91c and 92c of the support pins 91 and 92, and the spherical grooves (94d and 97d) of the support wheels 93 and 96, to absorb the load. Thus the impact load is prevented from being transferred to the load support rollers 95 and 98 of the wheels. This enhances the hoist driving efficiency and prevents the hoist from escaping the guide-rail.

The patent application also describes a second embodiment of the invention as seen in Fig 4 and of slightly different construction with support rollers in alternative positions on the main girder.

As shown in Fig 3, a falling down protector (159) may also be provided as four units.

About the patent

This article is an edited version of WIPO international patent application number WO/2008/010643, published on January 24 2008. The WIPO application was filed on May 25 2007 and an International Search Report has been made. The inventor, Duck-Rae Cho, works for the joint applicant, KG Inc. of Incheon City, Republic of Korea.

Marketing

KG markets the invention as its LS (LowSpace) Crane range. This is available in a wide range of dimensions with maximum loads from 2-40t. Additional features are VWF inverter control and a new design of saddle.

Disclaimer

This article is an edited version of the patent and may omit legally or technically important text. To see the full patent go to www.hoistmagazine.com/patents.