Weighing scales – Computer – Electrical
Reexamination Certificate
1999-12-30
2001-11-06
Gibson, Randy W. (Department: 2859)
Weighing scales
Computer
Electrical
C177S2100EM, C177S2100FP
Reexamination Certificate
active
06313415
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus for using an electronic scale to weigh articles.
BACKGROUND OF THE INVENTION
In the electronic scale art, see
FIG. 1
, it is known to send an analog signal from a load cell in response to an object being placed upon the load cell. The signal is then amplified and sent to an analog-to-digital converter. The digital output of the analog to digital converter, i.e., the signal representing the weight, is processed by a microcontroller and displayed to the user.
However, requiring a separate amplifier and a separate analog-to-digital converter increases the cost and complexity of an electronic scale. Additionally, standard timers/counters in typical microcontrollers have limitations which affect resolution particularly when one sole timer/counter is relied on. Therefore, achieving high resolution while using a less expensive, and a less complex, scale for weighing articles is desirable and needed in the art.
SUMMARY OF THE INVENTION
In the present invention, an analog signal from a load cell is converted, with circuitry on the load cell apparatus, directly to a pulse width modulated output signal which is suitable for reading by a microcontroller. This signal represents the weight of the article on the scale and it is directly readable by a microcontroller without amplification or analog to digital conversion. Therefore, an amplifier or an analog-to-digital converter is not required. This simplification greatly reduces the cost and complexity of the scale. Further, a method of combining the use of multiple timer/counters with different rates of operation on the microcontroller is incorporated into the operation of the scale which provides a high resolution signal required for a high resolution scale without requiring additional hardware. Therefore, the invention provides a much simpler, and much less costly, electronic scale apparatus than is known in the art while also enabling a method of generating high resolution data.
Therefore according to a first aspect of the invention an electronic scale for weighing an object placed thereon is provided. The electronic scale comprises a load cell with terminals for providing an output voltage proportional to the weight of the object placed on the load cell; a pulse width modulated signal generator responsive to the output voltage from the load cell so as to generate a pulse width modulated output signal responsive to said output voltage; and a microcontroller responsive to the pulse width modulated output signal generated by the pulse generator so as to generate a weight data having a value proportional to the duty cycle of the pulse width modulated output signal. The microcontroller may include programmable timer/counter arrays (PCAs) to time the pulse width modulated output signal used by the microcontroller to generate the weight data.
According to a second aspect of the invention, the scale may include a memory for the storage of a number of count overflows, wherein the microcontroller includes a first high resolution timer/counter and a second timer/counter, the first timer/counter is clocked to count at a faster rate than the second timer/counter, wherein the second timer/counter is preset with a predetermined count value so that it overflows at the same count value as the first timer/counter. The scale may also be configured so that the counts in the first and second timer/counters are stopped upon detection of a rising edge or falling edge transition in the pulse width modulated output signal and the value of the first timer/counter and the overflow value is saved as a representation of the pulse width of the High pulse or Low pulse respectively. The microcontroller may be an Intel® 8XC51FX based microcontroller or other microcontroller.
According to a third aspect of the invention, a method of connecting a load cell with a pulse width generator to a microcontroller is disclosed, comprising the steps of: placing an article on a load cell to generate an analog signal from the load cell which is proportional to a weight of the article placed on the load cell; sending the analog signal to a pulse width generator connected to the load cell which directly converts the analog signal to a pulse waveform signal which is readable by a microcontroller connected to the pulse width generator without amplification or use of an analog to digital converter.
According to a fourth aspect of the invention, a method for determining the weight of an article placed on a load cell is disclosed comprising the steps of: placing an article on the load cell to generate an analog signal from the load cell which is proportional to the weight of the article; sending the analog signal to a pulse width modulated signal generator which directly converts the analog signal to a pulse width modulated signal which is readable by a microcontroller, said pulse width modulated signal having a duty cycle proportional to the analog signal, said pulse width modulated signal generated without amplification or use of an analog to digital converter; wherein the pulse width modulated signal contains rising edges and falling edges which form a duty cycle proportional to the weight of the article placed on the load cell; sending the pulse width modulated signal to a Programmable Counter Array (PCA) capture module of a microcontroller to enable a first timer/counter and a second timer/counter in the microcontroller. This is accomplished by setting the first timer/counter and the second timer/counter to operate at different rates wherein the first timer/counter operates at a rate which is faster and has higher resolution than the second timer/counter; presetting the second timer/counter to a specific value such that it experiences overflow at the same time that the first timer/counter experiences overflow in a synchronized manner; starting the timer/counters upon detection of a rising edge or a falling edge by the Programmable Counter Array (PCA) capture module; interrupting upon overflow of the second timer/counter, incrementing an overflow count value of the second timer/counter in a memory, logically adding a synchronization value to the second timer to enable the second timer to remain synchronized with the first timer, and returning from interrupt; interrupting the timer/counters upon detection of a subsequent rising edge or a subsequent falling edge by the Programmable Counter Array (PCA) capture module; storing in a memory a value present in the first time/counter upon interrupt; combining the overflow count value of the second timer/counter with the value from the first timer/counter to form a value which represents the High or Low portion of the pulse width modulated signal. These High and Low data values are converted to a high resolution value in the microcontroller which represents a weight value for the article placed on the load cell. The microcontroller may operate at a predetermined frequency of oscillation (Fosc) wherein: the second timer/counter operates at the rate of Fosc divided by 4 (Fosc/4), and the first timer/counter operates at the rate of Fosc divided by 2 (Fosc/2).
REFERENCES:
patent: 4730499 (1988-03-01), Gianella et al.
patent: 5419204 (1995-05-01), Yamaguchi et al.
patent: 5864295 (1999-01-01), Jarocha
patent: 5877637 (1999-03-01), Trofimenkoff et al.
patent: 5900592 (1999-05-01), Sohns et al.
Bass Edward R.
Maher James P.
Miller Kenneth G.
Gibson Randy W.
Melton Michael E.
Meyer Robert E.
Pitney Bowes Inc.
Reichman Ronald
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