Platform Transducer Beams

The present invention relates to an improvement in platform transducer beams, and in particular in platform load cells (PLCs). The improvement protects these PLCs from damage that may be caused during handling or shipping of the PLCs.

PLCs are strain gage transducer beams which may be secured to a platform in many different arrangements to form a scale. Typically, a platform structure is supported in each corner by a single transducer beam arranged between the platform and a base. The transducer beams are provided with strain gages which change in electrical resistance in response to strain which is thus measured by a suitable bridge circuit.

The PLCs are machined out of a single piece of metal to precise specifications and perform very well with regard to linearity, hysteresis, and creep. However, the lower capacity units (0.5 to 20 lbs.) are somewhat susceptible to damage during handling and/or shipping. This damage may occur at any manufacturing or processing step starting after the machining operation and including anodizing or plating, wiring, and testing operations. Especially the very low capacity 0.5, 1, 2, and 5 lb. units, which are rather delicate, are subject to this trouble. Considerable efforts have been made to protect these delicate units during processing, but these efforts have not been very successful.

In view of the foregoing it is the aim of the invention to provide an improvement in platform transducer beams that will simply and cheaply protect the transducer beams from damage during processing and shipment. Such protection shall be available until a scale equipped with such PLCs reaches its final destination.

According to the invention holes are drilled and threaded through the transducer beam at least at one critical location and a safety screw or screws serve to secure beam sections of the whole transducer beam to each other. The transducer beam comprises at least two beam sections rigidly connected to each other at their respective ends. These sections are separated from each other by a narrow slot formed by machining or milling. This slot allows the transducer beam to bend at its sensing or flexing portions in such a way that strain gages secured to the flexing portions can measure strain. The threaded holes are drilled so that the safety screws pass through the slot or slots for securing the beam sections, on either side of a slot to each other. The addition of these threaded holes in no way compromises the performance of the transducer beam. Adding safety screws results in a much stronger structure in regard to loads that may be accidentally applied to the transducer beam during handling or shipping.

In order that the invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 shows a side view partially in section of a double bending beam transducer of the platform load cell type improved according to the present invention;

FIG. 2 shows a view in the direction of arrow A in FIG. 1 and illustrating the directions relative to which the transducer beam has been made insensitive; and

FIG. 3 shows another type of transducer beam improved according to the present invention.

FIG. 1 shows a typical platform load cell 1 manufactured from a single block and comprising beam sections 2 and 3 separated by a slot 4 and drilled holes 5 and 6, and beam section 7 separated from beam section 3 by a slot 8 and drilled holes 9 and 10.

In the implementation of this invention, the holes 11 are drilled and tapped during the machining of the PLC, before the slots 4 and 8 are cut. Then, just before removing the PLC from the holding jig, the two safety screws 12 of the set screw type are inserted into the holes 11. These screws preferably are made of a suitable high strength plastic material such as nylon. A plastic safety screw is advantageous because it can be installed immediately after machining and can be left in place during the subsequent anodizing or plating operations and during any following manufacturing, assembling and shipping operations, except during testing.

In FIG. 2 the arrows a, b and c show the directions of adverse loads that could damage a load cell during handling. According to the invention, when the two safety screws 12 are in place, the entire structure of the PLC becomes stronger. The PLC is protected against adverse loads that can be accidentally applied to the PLC during handling, particularly in the directions shown by arrows a, b and c. Through the simple expedient of adding the safety screws 12, a substantial portion of the loads a, b and c is taken up by the screws 12 which prevent transmitting of these forces to the sensing sections 13 and 14 carrying the strain gages not shown.

FIG. 3 shows another transducer beam 20 with two beam sections 21 and 22 separated by drilled holes 23 and 24 and by slot 25. A single safety screw 26 can be installed in a threaded hole 27 to secure the transducer beam against accidental handling damage.

As mentioned, the safety screws 12, 26 are left in place during all of the manufacturing operations after the initial machining, except when the units are tested. Testing requires only a short period of time and is performed by skilled operators, so there is less danger of damage during testing. After testing, the safety screws are reinserted to greatly reduce the susceptibility of the units to damage during shipment. The screws may be, or rather should be, left in the PLCs even after these units are incorporated in platform type scales. The user of the scale can then remove the safety screws after the scale is installed or in place at its final destination.

By adding safety screws to the transducer beams according to the teaching of the invention, a feature is provided that greatly reduces the susceptibility of the PLC units to damage due to handling in the machine shop and through subsequent operations prior to the ultimate use by the final customer, without compromising the performance of the units.

Although the invention has been described with reference to specific example embodiments, it will be appreciated that it is intended to cover all modifications and equivalents within the scope of the appended claims.