3. PREAMBLE TO THE DESCRIPTION

a. Background and the prior art:

Material handling is an essential task in commercial, industrial and construction activity. Cranes and other material handling equipment are designed for lifting a certain maximum load. The operator and personnel who are handling these machines may not be aware of magnitude of the load being lifted. In such cases, if the magnitude of load being lifted exceeds the capacity, it may cause accidents. Safe operation solely depends on operators' ability to estimate the load being lifted. Any mistake on the part of the operator may result in an accident leading to loss of life and damage to equipment and materials being handled. Use of a crane scale which measures and displays the load being lifted will help in preventing overload and any possible accidents due to overloading.

Crane scales currently available consist of a modified crane hook with an Eye at the top for suspending it from the crane and at the bottom is the hook for lifting the load. In between these two is the middle part called load determination element. Load sensing transducers are mounted in this region and are connected to associated electronic circuit for processing the electrical signal and the digital output is displayed as load. The major drawback of this system is that the crane hook is to be modified to provide sufficient space for mounting transducers for sensing the load. Size of the hook also becomes larger. As the whole of this part is to be designed and manufactured precisely considering the safety aspect, the whole system becomes costlier. US Patent No. 5,072,798 (Crane Scale Load Repeating Device, 1991) describes a crane having load measuring device which works on the above principle.

b. Objectives of the Invention:

The objectives of the present invention are to

1. Provide an economical and safe method of measuring load that is being lifted by a crane which will help in preventing any accidents that may occur because of overloading

2. Provide the load measuring device which can be incorporated in the crane hook, without making any structural modifications to the hook

c. Summary of the invention:

This invention involves identifying a critical location in a crane hook, preparing the surface and bonding the load sensing transducers at this critical location in an appropriate fashion. The transducers are connected to form a bridge circuit. Output of the bridge circuit is fed to an electronic data processing unit which, in turn will amplify, digitize the electrical signal and display the load. The displayed load is properly calibrated (for the entire load range) by applying known load to the crane hook. Once calibrated, the device will be ready for use to measure any unknown applied load. As no structural modifications are made to the hook, it is safe to use this device and, also, there is no increase in size of the hook assembly.

COMPLETE SPECIFICATION

The following specification particularly describes the invention and the manner in which it is to be performed

4. DESCRIPTION

A. Brief description of the drawings:

To assist in understanding the invention, reference will now be made to the accompanying drawings which are as follows:

Figure 1: Crane Hook showing the region of mounting load sensing transducers

Figure 2: Photograph of the crane hook with load sensing transducers mounted

Figure 3: Block diagram of the load meter (electronic data processing unit)

Figure 4: Photograph of the load meter with load displayed.

In the following description, the part numbers are mentioned by numerals in brackets. Like numerals designate similar parts in all the figures / drawings. The photographs are included for better understanding of the equipment described herein.

B. Detailed description and preferred embodiment:

a. Principle of transducer application:

The load sensing transducer is an electrical resistance strain gage whose electrical resistance changes due to deformation. The gage is in the form a thin foil grid with two leads and is supported between paper or epoxy films. It is bonded using an adhesive on the member (crane hook in the present invention) which is subject to application of external load. The hook deforms due to the load and the strain gage bonded to the surface also deforms causing a change in its electrical resistance.

When the load is being lifted by the hook, different sections of the hook are subjected to a combination of tensile load and bending moment. The section where their combined effect is maximum is the critical section. The strain and hence the deformation at this section is maximum. Strain gages are bonded at this critical section in such a way that the output response is maximum. The output response of these gages is combined by connecting them to form a bridge circuit. The output of the bridge circuit is proportional to the applied load. The sensitivity of load measurement by the proposed method is better than that by the conventional crane scale because, the section where the gages are bonded experiences both axial load and bending moment. Bending moment causes greater strain and hence larger deformation than the axial load alone. This results in greater sensitivity in load measurement by the proposed method.

b. Detailed description:

Figure 1 shows the pictorial view of the crane hook on which the load sensing transducers are bonded. Part (1) shows the region of the crane hook at which loading is done. Part (2) region for bonding load sensing transducers and location of this region is decided by careful analysis of the resulting strain pattern. Before the gages are bonded, the hook surface at this region is prepared by cleaning it using chemical solvent. The gages are bonded using an adhesive, cured and then they are connected to form a bridge circuit on the upper half (2) of the hook. Part (3) shows transducer protection enclosure to prevent any damage that may occur during loading.

Figure 2 shows the photograph of the hook with load sensing transducers bonded and protected using an enclosure in actual experimental condition.

Block diagram of the load meter with transducer bridge is shown in Figure 3. The transducer bridge (4) is connected to the load meter (9). Load meter consists of an amplifier (5) which amplifies the bridge output with required gain. The amplified signal is converted to digital signal using Analog to Digital Converter, ADC (6). The digitized signal is displayed as the load on the display panel (7). The required power to transducer bridge and other units is supplied from line current or battery (8).

Figure 4 shows the photograph of the load meter which houses all the components (5) to (9), shown in Figure 3. The load is indicated on the display panel (10). The load meter can be fixed at the top of the hook itself and load display can be viewed remotely on a hand held display panel. The device is calibrated by applying known load to the hook. The display is properly set to the correct load by varying the amplifier gain. Once calibrated, the device will be ready for use to measure load being lifted.

c. Operation:

When the power to the load meter (Figure 4) is switched on, the load meter is ready for use. As the load is lifted by the crane, the hook experiences deformation proportional to the load being lifted. This deformation is sensed by the load sensing transducers. The electrical signal from the transducer bridge is processed and displayed as load on the display panel of load meter. Load can be displayed remotely on a hand held display panel which will be convenient to the crane operator for safe operation.

d. Advantages:

This newly developed device for measuring load being lifted by crane using crane hook has many advantages. The crane scale presently available is to be purchased as a whole unit which incorporates modified hook. This is larger in size. Moreover, as the hook in Crane Scale has structural modifications, it has to be precisely designed, manufactured with precision and therefore, it will be costlier. The new device does away with all these shortcomings as the existing hook itself is used for measuring load. This results in cost reduction. Moreover, as no structural modification is required, safety is not compromised.

We claim

1. The "Device for Measuring Load on a Crane Hook", an additional device attached to crane hook for measurement of load on the crane hook, consisting of (1) crane hook which takes the load and undergoes deformation, (2) transducers, bonded at critical location on the crane hook, which experience the same mechanical deformation and convert it into an electrical signal, (3) a bridge circuit for combining signals from different transducers bonded on the hook and (4) a load meter for converting this electrical signal to display the load.

2. Crane hook, referred in claim (1), refers to crane hook, used for lifting loads (in industries, construction sites, harbors or elsewhere)

3. Critical location, referred in claim (1), refers to an area where, due to application of load, the strain and hence deformation is maximum and this area is identified by analysis of resulting strain pattern in the hook.

4. Transducers, referred in claim (1), are electrical resistance strain gages, which are bonded firmly using a strong adhesive at the critical location, in the upper half of the crane hook

5. Crane hook, referred in claim (1), on loading, undergoes deformation (strain) proportional to degree of loading which is maximum at the critical location in the hook.

6. The transducers referred in claim (1) bonded at the critical section on the hook, experience same strain as experienced by the hook and converts this strain into an electrical signal.

7. The bridge circuit, referred in claim (1), combines the electrical signals from all the transducers bonded on the hook.

8. Load meter, referred in claim (1), amplifies the electrical output from the bridge circuit and digitizes the signal and displays it (as a measure of load) and the digital display is calibrated with standard set of loads, for the entire range of use of the crane hook.

9. 'Device for Measuring Load on a Crane Hook', referred in claim (1), is substantially described herein with reference to the drawings and photographs accompanying this specification.

10. The concept used in 'Device for Measuring Load on a Crane Hook', referred in claim (1), is also applicable to other sizes of crane hooks.