LIFTING DEVICES

Field of the Invention

Under the Statutes of the Swedish National Board of Occupational Safety and Health AFS 1980:19, all lifting devices with a ground load exceeding 1 tonne are to be provided with load-limiting means for protection against overload and personal injuries. The present invention relates to a load simulator, which is adapted to be used when checking and testing the function of the load-limit¬ ing means. Background Art

Provisions regarding inspection and testing of load-limiting means are to be found in Swedish Standard SS 768 06 01 "Cranes - Load-Limiting Means - Inspection and Testing". According to this standard, load-limiting means are to be tested according to the manufacturer's instructions as a rule once a year. The testing is to take place in such manner that the real function is achieved. For cranes, which are subjected to recurrent inspections at an official testing centre, it is stated that the surveyor is bound to make sure that the load- limiting means has been tested as to function. The stan¬ dard contains an explicit ban on use of the mechanism of the lifting device during the endurance test. The testing is instead carried out by static load by means of a so- called lever block or some other hand-operated pulling device in combination with a dynamometer, load transducer or the like and a traction wire passing over a block fix¬ ed in the draw hook of the lifting device and down to a fixed point in the floor, a heavy vehicle or the like. For the loading operation, use is made of different weights, which are connected to the lever block or the hand-operated pulling device. These weights are kept between the different testing occasions and therefore

cause drawbacks not only in terms of handling but also in terms of storing.

Swedish Patent 466,818 discloses the testing of one type of load-limiting means that has two backing rollers. During testing according to this patent, the load-limit¬ ing means is disconnected from the lifting device and arranged on a fixed base in order to simplify checking. This patent publication indicates no possibility of test¬ ing of the load-limiting means in its place in the lift- ing device. The testing method is complicated by necessi¬ tating partial dismounting of the lifting device, which takes time and requires professional skill.

Prior-art devices and methods for testing the load- limiting means of lifting devices thus suffer from va- rious drawbacks. The testing according to Swedish Stan¬ dard thus requires weights which must be handled and stored. In the device and the method according to the above-mentioned Swedish patent, dismounting of the load- limiting means and testing thereof at a separate testing centre are required.

One object of the present invention is to obviate or, in any case, considerably reduce these drawbacks. A further object of the invention is to provide a testing device which can be used for various types of lifting devices and is not connected to a lifting device having a predetermined load capacity.

Summary of the invention According to the invention, these and other objects are achieved by means of a load simulator which is de- signed as stated in claim 1. The subclaims define parti¬ cularly preferred embodiments of the invention.

Summing up, for the testing of load-limiting means in lifting devices use is to be made of a load simulator, which has a loading device and a load-sensing device for indicating the applied force. According to the invention, the loading device comprises a force-absorbing spacing device and a pulling device. The spacing device serves

as abutment between the pulling device and the girder arrangement of the lifting device and is therefore at one end connectible to the girder arrangement and at the other end connected to one end of the pulling device. The other end of the pulling device is in turn designed to be connected to the lifting means of the lifting device.

A great advantage of the invention is that the load simulator can be used for testing of many different lift¬ ing devices of various lifting capacity. A further advan- tage is that there is no longer any need of using sepa¬ rate weights, which are to be handled in connection with the testing procedure and are then stored in the period between the following annual inspections. A further ad¬ vantage is that the device constitutes a complete testing device, which comprises pulling means, abutment and load- sensing device to be connected to the girder arrangement and the ordinary lifting means of the lifting device that is to be tested. No actual modification of the device is necessary, and besides the use of the testing device or load simulator will imply a testing not only of the load- limiting means but also of the connection and normal function thereof in the lifting device. One more advan¬ tage of the invention is the possibility of checking in a simple manner also the ordinary transducer of the load- limiting means by comparing the measured value obtained from the transducer of the load simulator and the measur¬ ed value from the ordinary transducer of the load-limit¬ ing means. It will therefore also be easy to check the linearity of the load-limiting means. By the load simu- lator according to the invention being a complete unit, which by simple measures is connected to the girder ar¬ rangement of the lifting device and the ordinary lifting means thereof, no disconnection of the load-limiting means is necessary. For the same reason, the lifting device can be tested without any modifications.

It is thus an advantage of the invention that the load simulator can be easily arranged on the lifting

device. The invention makes it possible to test, in a simple and rational fashion, load-limiting means inde¬ pendently of the type and function thereof. The testing will be considerably easier than prior-art testing methods when the load-limiting means is dismounted or when weights or a fixed point in the floor are used to effect the loading.

Brief Description of the Drawings Fig. 1 is a side view of an example of a load simulator which is designed according to the present inven¬ tion and is connected to the girder arrangement and ordinary lifting means of a lifting device. Fig. 2 is a side view of the load simulator and the lift¬ ing device as seen from the left in respect of Fig. 1.

Fig. 3 is a perspective view of the actual load simula¬ tor.

Description of Preferred Embodiments Figs 1-3 illustrate a preferred embodiment of the load-simulator in two side views and one perspective view. In this preferred embodiment, a spacing device 1 or an abutment is designed as a truncated pyramid, the corners of which consists of compressive-force-absorbing oblique struts 7. These are inclined outwards from an end plate 8 and extend up to an annular mounting flange 9. The mounting flange is adapted to be connected in some suitable manner to the girder arrangement 6 of the lift¬ ing device 2 to be tested. The mounting flange 9 also constitutes a tensile stress absorbing element, which holds the ends of the oblique struts 7 together and pre¬ vents them from moving away from each other when the load simulator is being used. The end plate 8 at the narrow end of the spacing device constitutes a mounting for a pulling device 5, which in this case is a pneumatic or hydraulic piston-and-cylinder assembly, whose other end is adapted to be connected to the ordinary lifting means 3 of the lifting device 2. The piston-and-cylinder assem-

bly is in conventional manner connected to a compressed air pump or hydraulic pump via conduits (not shown in detail ) . For checking the pressure in the piston-and- cylinder assembly a pressure gauge is provided, which in this case serves as load-sensing device 4 for check¬ ing the applied force.

Within the scope of the invention, the spacing device 1 can be designed in other manners as well. One possibility is to design it as a cone, a cylinder or a girder while taking into consideration that the function of the spacing device 1 is to absorb compressive forces, which arise when the pulling device 5 subjects the lift¬ ing device 2 to pulling forces. In the embodiment illu¬ strated, the pulling device 5 is designed as a piston- and-cylinder assembly, but also other pulling devices can be utilised, for instance a capstan or some other pulling device for producing traction in the rope arrangement 10 of the pulling device 2 and, thus, testing of the load- limiting means of the lifting device 2. Within the scope of the invention, it is possible to use instead of a pressure gauge also other load-sensing devices 4. Thus, use can be made of a load cell between the rope arrange¬ ment 10 of the lifting device 2 and the pulling device 5, or a load cell between the spacing device 1 and the pull- ing device 5. The above-mentioned annular mounting flange 9 can also be replaced, for instance by tensioning belts or struts that are fixed a distance down on the struts 7 of the spacing device 1 and in this manner interconnect them to achieve the same function as above.