A present weigh module used in electronic balances mainly bases on the principle of electromagnetic force compensation. It consists of a large number of die cast parts and other mechanical parts assembly. Although the production technology is mature, with the development of technology improvement, requirements need to be put forward on weigh module used in electronic balances, such as smaller size, higher precision, wider weighing range, lower costs, more simple assembly and the like. As a result, a traditional weigh module assembled by a large number of die cast parts and other mechanical parts is restricted by the development of technology (hereinafter referred to as the whole assembly type weigh module) due to large volume, multiple components, complex assembly, big assembly tolerance, unstable quality.
There are manufacturers that produce highly integrated one-piece weigh modules, module as disclosed in U.S. Pat. No. 6,886,418 B2, DE 20 007 781 U1 or US 2011 10 315 458 A1. The main structure such as the load-receiving portion, the lever, the fixing portion, and the parallel-guiding members are separated by the narrow wire cutting groove or grooves of CNC machining. But the process is complex, high rejection rate, cost of the machining are relatively high. Some manufacturers also produce semi-integrated weigh modules, a weigh module of this type is disclosed for example in U.S. Pat. No. 6,472,618 B1. The main structure such as the load-receiving portion, the fixed portion, and the parallel-guiding members are integrated structure formed by machining, but the structure layout is unreasonable, because of inconvenient assembly and difficulties to achieve a large lever ratio with one single lever.
One kind of parallel-guiding mechanism for an electronic balance includes a load-receiving portion, an end portion and parallel-guiding members connecting the load-receiving portion to the end portion. The load-receiving portion, the end portion and the parallel-guiding members are assembled by thread joint. This kind of assembly needs a lot of time in assembling.
JPH 11 0 51756 discloses a weigh module including a support base, a lever and a parallel-guiding mechanism, which includes a load-receiving portion, a fixing portion and parallel-guiding members. The load-receiving portion and the fixing portion are connected by the parallel-guiding members namely by an upper parallel-guiding member and a lower parallel-guiding member. The parallel-guiding mechanism further includes a mounting member on the load-receiving portion that disposes outside of the space formed between the upper parallel-guiding member and the lower parallel-guiding member. The lever is connected to the mounting member of the load-receiving portion by a force-transmitting member forming a fulcrum mechanism. This kind of weigh module occupies a large volume. The mounting member is mounted to the end portion by thread joint, it takes a lot of time to assemble them together and the accuracy is lowed.
In order to solve these shortcomings, this invention provides an improved weigh module in order to overcome the defects in the prior art.