Fail-safe circuit for a control system
First Claim
1. A fail-safe circuit for a control system, comprising:
- (a) a main control circuit which produces and sends a first control signal to a controlled device for controlling the controlled device;
(b) a back-up control circuit which operatively produces and sends a second control signal to the controlled device in place of the first control signal when the main control circuit fails, the back-up control circuit having first means for recognizing a malfunction of said main control circuit and proper operation of the back-up control circuit and second means for generating a unique switching signal when said first means recognizes the malfunction of said main control circuit and proper operation of the back-up control circuit;
(c) a switching circuit for switching between the first and second control signals to transmit either of the first and second control signals to the controlled device depending on a presence or absence of the unique signal generated from said second means; and
(d) a switching control circuit for controlling the switching circuit to enable transmission of the second control signal produced from the back-up control circuit to the controlled device when the unique switching signal is received from the back-up control circuit and for enabling transmission of the first control signal produced from the main control circuit when the unique switching signal is not received from the back-up control circuit, thereby preventing an erroneous switching of the switching circuit when the main control circuit is operating properly and the back-up control circuit generates a faulty switching signal.
1 Assignment
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Accused Products
Abstract
A highly reliable, fail-safe circuit for a control system wherein a controlled device will always receive a control signal derived from a main control circuit when the main control circuit operates normally even if a back-up control circuit backing up at least one function of the main control circuit which is a minimum requirement for an operation of the controlled device fails or wherein a controlled device will receive a control signal derived from the back-up control circuit when the main control circuit fails. Replacement of the control signal from the main control circuit with a back-up control signal from the back-up circuit is carried out only when the back-up circuit outputs a particular signal at or near a predetermined frequency or alternatively when the back-up circuit outputs a plurality of parallel logical signals in a predetermined combination.
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Citations
16 Claims
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1. A fail-safe circuit for a control system, comprising:
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(a) a main control circuit which produces and sends a first control signal to a controlled device for controlling the controlled device; (b) a back-up control circuit which operatively produces and sends a second control signal to the controlled device in place of the first control signal when the main control circuit fails, the back-up control circuit having first means for recognizing a malfunction of said main control circuit and proper operation of the back-up control circuit and second means for generating a unique switching signal when said first means recognizes the malfunction of said main control circuit and proper operation of the back-up control circuit; (c) a switching circuit for switching between the first and second control signals to transmit either of the first and second control signals to the controlled device depending on a presence or absence of the unique signal generated from said second means; and (d) a switching control circuit for controlling the switching circuit to enable transmission of the second control signal produced from the back-up control circuit to the controlled device when the unique switching signal is received from the back-up control circuit and for enabling transmission of the first control signal produced from the main control circuit when the unique switching signal is not received from the back-up control circuit, thereby preventing an erroneous switching of the switching circuit when the main control circuit is operating properly and the back-up control circuit generates a faulty switching signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. The fail-safe circuit according to claim 14, wherein said switching circuit transmits the first control signal when a third control signal, derived from the switching control circuit produced when the unique signal is received, is at a grounded voltage level and further comprising a pull-down resistor connected between a line connecting said switching circuit and switching control circuit and ground.
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15. The fail-safe circuit according to claim 15, wherein said switching control circuit transmits the first control signal when the third control signal is at a higher of two voltage levels and further comprising a pull-up resistor connected between a line connecting said switching circuit and switching control circuit and a positive power supply.
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16. The fail-safe circuit according to claim 16, wherein the second control signal satisfies minimum requirements of control of the controlled device.
Specification