Span adjusting device for weigher

#This invention relates to an improved automatic span correcting device for weighers. The inventive device is especially useful when incorporated in a so-called combination weighing machine.

#In a weigher having a digital indicator, the digital value on the indicator does not always coincide with the digital value which corresponds to the analog weight of product put on the weighing cradle of the weigher. For example, assume a digital value of "1000" on the indicator is to correspond to an analog weight of "100 grams". If the analog output of the weigher is converted by an analog to digital converter into a digital value of "1010" when the weigher is loaded with product of 100 gram weight, the digital value must be corrected to "1000". Such correction is referred to as "span correction" in the field of weighing equipments. This invention relates to a device for automatically effecting such correction.

#The opened Japanese patent specification No. 58-95220 discloses a method of effecting such span correction. In this method, a weigher is first zero-corrected in its unloaded state. Then, the weigher is loaded with a reference test weight having a known weight value and the resultant weight signal is divided by the known weight value to obtain a span correction coefficient which is stored in a register. Thereafter, any weight signal output from the weigher is multiplied by this coefficient to obtain a corresponding span-corrected value of the weight.

#In the drawings:

#FIG. 1 is a block diagram representing an automatic span correcting device for weighers according to this invention;

#FIG. 2 is a front view representing a first embodiment of the device of this invention;

#As shown in FIG. 1, the device of this invention includes a load detector 2, such as weigher, for weighing product and producing a weight signal indicative of the weight of the product, a first memory 4 for storing nominal weight values of a plurality of reference test weights; and a second memory 6 for storing boundary weight values corresponding respectively to the nominal weight values stored in the first memory 4. The weight values stored in both the first and second memories 4 and 6 form corresponding sequential pairs in order of magnitude and these pairs are read out sequentially from the memories 4 and 6 by read-out means 8. A comparator 10 compares the weight signal from the load detector 2 with two sequentially adjoining boundary weights from the second memory 6 and produces an output signal when the weight signal falls between the current boundary weight and the preceeding boundary weight. Transfer means 14 supplies the current weight value from the first memory 4 to a span correction coefficient calculating means 12 in response to the output signal from the comparator 10. A span correction coefficient is calculated from the weight signal supplied by the load detector 2 and the current weight value read out of the first memory 4.

#Referring next to FIGS. 2 and 3, a first preferred embodiment of the device of this invention includes a load cell 20 fixed at an end to a support bracket 18 which stands erect on a base 16. A weighing hopper 22 is coupled to the other end of the load cell 20. Strain gauges 24 are attached to four flexures of the load cell 20 for detecting deflection thereof to produce an analog weight signal indicative the weight of product placed in the hopper 22.

#A support arm 26, an end of which is pivoted at a midpoint of the bracket 18 and the other end of which is forked to support a reference check weight 28, is disposed on one side of and along the load cell 20. The support arm 26 is coupled at its midpoint to a plunger 30a of an air cylinder 30 disposed on the base 16. A coiled spring 32 is disposed between the support arm 26 and a cylinder casing 30b for urging upward the support arm 26 and thus supporting the check weight 28. A V-shaped receptacle 34 is disposed in the side of the load cell 20 so that the receptacle makes no contact with the check weight 28 when the arm 26 is urged upward by the spring 32 and the receptacle supports the arm 26 when it is pulled down by the air cylinder 30. Accordingly, actuation of the cylinder 30 pulls down the support arm 26 against the coiled spring 32 and results in loading of the load cell 20 with the check weight 28 and deactuation thereof causes the spring 32 to raise the arm 26 and results in unloading of the check weight 28.