Electronic weighing apparatus utilizing surface acoustic waves
First Claim
1. An electronic weighing apparatus, comprising:
- a) a displaceable elastic member means for receiving a load and being displaced by the load such that the displacement of said elastic member means is related to the weight of the load;
b) a first piezoelectric transducer having a first substrate and one of a first surface acoustic wave (SAW) transmitter and a first SAW receiver, said first piezoelectric transducer being coupled to said elastic member such that said displacement of said elastic member causes a corresponding displacement of said first piezoelectric transducer;
c) a second piezoelectric transducer having a second substrate and the other of said first SAW transmitter and said first SAW receiver, said second piezoelectric transducer being mounted in close proximity to said first piezoelectric transducer;
d) a first amplifier having an input and an output, said input of said first amplifier being coupled to said first SAW receiver and said output of said first amplifier being coupled to said first SAW transmitter such that said first piezoelectric transducer, said first amplifier, and said second piezoelectric transducer form a first oscillator having a first output frequency; and
e) processor means coupled to said output of said first amplifier, whereindisplacement of said elastic member means causes a displacement of said first piezoelectric transducer relative to said second piezoelectric transducer and thereby changes said first output frequency, and said first output frequency is used by said processor means to determine an indication of the weight of the load.
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Accused Products
Abstract
An electronic weighing apparatus includes a base which supports a cantilevered elastic member upon which a load platform is mounted. The free end of the elastic member is provided with a first piezoelectric transducer and a second piezoelectric transducer is supported by the base. Each transducer includes a substantially rectangular piezoelectric substrate and a pair of electrodes imprinted on the substrate at one end thereof. The transducers are arranged with their substrates substantially parallel to each other with a small gap between them and with their respective electrodes in relatively opposite positions. The electrodes of the second transducer are coupled to the input of an amplifier and the output of the amplifier is coupled to the electrodes of the first transducer. The resulting circuit is a positive feedback loop with a "delay line" in which a surface acoustic wave in one substrate is effectively induced into the other. When a load is applied to the load platform, the free end of the cantilevered elastic member moves and causes the first transducer to move relative to the second transducer. The movement of the first transducer relative to the second transducer causes a change in the frequency at the output of the amplifier which is used to determine the displacement of the elastic member and thus the weight of the applied load.
14 Citations
19 Claims
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1. An electronic weighing apparatus, comprising:
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a) a displaceable elastic member means for receiving a load and being displaced by the load such that the displacement of said elastic member means is related to the weight of the load; b) a first piezoelectric transducer having a first substrate and one of a first surface acoustic wave (SAW) transmitter and a first SAW receiver, said first piezoelectric transducer being coupled to said elastic member such that said displacement of said elastic member causes a corresponding displacement of said first piezoelectric transducer; c) a second piezoelectric transducer having a second substrate and the other of said first SAW transmitter and said first SAW receiver, said second piezoelectric transducer being mounted in close proximity to said first piezoelectric transducer; d) a first amplifier having an input and an output, said input of said first amplifier being coupled to said first SAW receiver and said output of said first amplifier being coupled to said first SAW transmitter such that said first piezoelectric transducer, said first amplifier, and said second piezoelectric transducer form a first oscillator having a first output frequency; and e) processor means coupled to said output of said first amplifier, wherein displacement of said elastic member means causes a displacement of said first piezoelectric transducer relative to said second piezoelectric transducer and thereby changes said first output frequency, and said first output frequency is used by said processor means to determine an indication of the weight of the load. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification