Controller for resistive heating element
First Claim
1. An apparatus for controlling the flow of current from a current source through a resistive heating element disposed on a surgical scalpel such that the resistive heating element is heated from an ambient temperature to a predetermined temperature, said apparatus comprising:
- voltage measuring means for sensing the magnitude of the voltage drop across the resistive heating element and for generating a voltage-representative signal having a value corresponding to the magnitude of the voltage drop so sensed;
current measuring means for sensing the magnitude of current flowing through the resistive heating element and for generating a current-representative signal having a value corresponding to the magnitude of the current so sensed;
resistance computing means for generating a computed resistance signal having a value corresponding to the predicted resistance of the heating element at the predetermined temperature, said resistance computing means including a calibration means which produces a first signal for use in generating said computed resistance signal, said first signal having a value corresponding to the resistance of the resistive heating element at the ambient temperature, said resistance computing means also including a temperature parameter means which produces a second signal for use in generating said computed resistance signal, said second signal having a value corresponding to a temperature parameter which varies as a function of the predetermined temperature;
ratio comparision circuit means for generating a control signal, said ratio comparison circuit means including a multiplying means connected to said current measuring means and said resistance computing means for deriving a product signal having a value which corresponds to the product of said values of said current-representative signal and said computed resistance signal, said ratio comparison circuit means also including a summing means connected to said multiplying means and said voltage measuring means for combining said product signal with said voltage-representative signal in order to generate said control signal; and
means connected to receive said control signal for regulating the flow of current between the current source and the resistive heating element in response to the magnitude of said control signal.
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Abstract
The controller of the present invention regulates the flow of current through a resistive heating element by computing the predicted resistance Rhot of the heating element at the desired temperature and then adjusting the voltage drop across and current flow through the resistive heating element until the relationship V=IRhot is satisfied. In an analog embodiment of the present invention, measurement of the voltage drop is obtained from a voltage amplifying circuit connected across the resistive heating element, while a measure of the current flow through the resistive heating element is obtained from a current amplifying circuit connected across a current measuring resistor in series with the resistive heating element. The output of the current amplifying circuit is multiplied by first and second variable gain amplifier circuits to produce a signal output representing the product of the current flow and the predicted resistance at the desired temperature. The signal from the voltage amplifying circuit and the product-representative signal from the two variable gain amplifier circuits are balanced in a control amplifier to produce a control signal having a value which varies as a function of the difference between the voltage-representative signal and the product-representative signal. The control signal is thereafter utilized to adjust the voltage drop across the resistive heating element until the current through the resistive heating element multiplied by the predicted resistance at the desired temperature, i.e., the product-representative signal, equals the voltage drop across the resistive heating element.
111 Citations
16 Claims
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1. An apparatus for controlling the flow of current from a current source through a resistive heating element disposed on a surgical scalpel such that the resistive heating element is heated from an ambient temperature to a predetermined temperature, said apparatus comprising:
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voltage measuring means for sensing the magnitude of the voltage drop across the resistive heating element and for generating a voltage-representative signal having a value corresponding to the magnitude of the voltage drop so sensed; current measuring means for sensing the magnitude of current flowing through the resistive heating element and for generating a current-representative signal having a value corresponding to the magnitude of the current so sensed; resistance computing means for generating a computed resistance signal having a value corresponding to the predicted resistance of the heating element at the predetermined temperature, said resistance computing means including a calibration means which produces a first signal for use in generating said computed resistance signal, said first signal having a value corresponding to the resistance of the resistive heating element at the ambient temperature, said resistance computing means also including a temperature parameter means which produces a second signal for use in generating said computed resistance signal, said second signal having a value corresponding to a temperature parameter which varies as a function of the predetermined temperature; ratio comparision circuit means for generating a control signal, said ratio comparison circuit means including a multiplying means connected to said current measuring means and said resistance computing means for deriving a product signal having a value which corresponds to the product of said values of said current-representative signal and said computed resistance signal, said ratio comparison circuit means also including a summing means connected to said multiplying means and said voltage measuring means for combining said product signal with said voltage-representative signal in order to generate said control signal; and means connected to receive said control signal for regulating the flow of current between the current source and the resistive heating element in response to the magnitude of said control signal. - View Dependent Claims (2, 3, 4, 5, 16)
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6. An apparatus for controlling the flow of current from a current source through at least one resistive heating element such that the resistive heating element is heated from an ambient temperature to a predetermined temperature, said apparatus comprising voltage measuring means for sensing the magnitude of the voltage drop across the resistive heating element and for providing a voltage-representative signal having a value corresponding to the magnitude of the voltage drop so sensed;
- current measuring means for sensing the magnitude of the current flowing through the resistive heating element and for generating a current-representative signal having a value corresponding to the magnitude of the current so sensed;
resistance computing means for generating a computed resistance signal having a value corresponding to the predicted resistance of the resistive heating element at the predetermined temperature, said resistance computing means including a calibration means which produces an ambient resistive signal for use in generating said computed resistance signal, said ambient resistance signal having a value corresponding to the resistance of the resistive heating element at the ambient temperature, said resistance computing means also including a temperature parameter means which produces a temperature parameter signal for use in generating said computed resistance signal, said temperature parameter signal having a value corresponding to a temperature parameter which varies as a function of the predetermined temperature;
ratio comparison circuit means for generating a control signal to regulate the flow of current from the current source to the resistive heating element, said ratio comparison circuit including a multiplying means connected to receive said current-representative signal and said computed resistance signal for generating a product signal having a value representing the product of said values of said current-representative signal and said computed resistance signal, said ratio comparison circuit also including a summing means connected to receive said product signal and said voltage-representative signal for outputting said control signal as a function of the difference between said value of said voltage-representative signal and said value of said product signal; and
means connected to receive said control signal for causing current to flow between the current source and the resistive heating element in response to said value of said control signal. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15)
- current measuring means for sensing the magnitude of the current flowing through the resistive heating element and for generating a current-representative signal having a value corresponding to the magnitude of the current so sensed;
Specification