Motor control circuit with a low voltage monitor
First Claim
1. In a control circuit for a motor of a crane that receives voltage from a power supply, the improvement comprising:
- a switch through which electric current flows to control the motor in response to a control signal applied to a control terminal of the switch;
a monitor circuit which detects whether voltage supplied to the control circuit exceeds a threshold level and responds by producing a sensor signal, wherein the threshold level is greater than a voltage produced by the motor operating in a regenerative mode during failure of the power supply; and
a switch circuit that responds to the sensor signal by producing the control signal that is applied to the switch.
1 Assignment
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Accused Products
Abstract
A control circuit for an overhead crane motor includes a low supply voltage monitor to disconnect the motor from the control circuit and ensure brakes engage in the event of interruption of power supplied to the crane. A sensor circuit detects whether voltage supplied to the control circuit drops below a predefined threshold level which is greater than a voltage magnitude produced by the motorN operating in a regenerative mode during a power interruption. A switching circuit responds to sensing supply voltage below the threshold level by disconnecting electrical current to a relay coil which causes contacts to open which result in the motor being electrically disconnected from the control circuit. As a result of that disconnection, voltage produced by the motor operating in a regenerative mode does not inhibit electrically controlled mechanical brakes from engaging.
24 Citations
18 Claims
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1. In a control circuit for a motor of a crane that receives voltage from a power supply, the improvement comprising:
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a switch through which electric current flows to control the motor in response to a control signal applied to a control terminal of the switch; a monitor circuit which detects whether voltage supplied to the control circuit exceeds a threshold level and responds by producing a sensor signal, wherein the threshold level is greater than a voltage produced by the motor operating in a regenerative mode during failure of the power supply; and a switch circuit that responds to the sensor signal by producing the control signal that is applied to the switch. - View Dependent Claims (2, 3, 4, 5)
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6. A low voltage monitor for a motor of a crane that receives voltage from a power supply, the low voltage monitor comprising:
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first and second terminals across which is to be applied a voltage to be monitored; an output terminal; a first voltage divider coupled between the first and second terminals, and having a first node; a capacitor connected between the first node and the second terminal; an output transistor having a first control electrode, and a conduction path connected between the second terminal and the output terminal; and a transistor drive circuit coupled to the output transistor to apply a voltage to the control electrode in response to a voltage across the capacitor. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13)
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14. A low voltage monitor for a dc series motor of a crane that receives voltage from a power supply, the low voltage monitor comprising:
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first and second terminals across which is to be applied a voltage to be monitored; an output terminal; a first voltage divider coupled across the first and second terminals, and having first and second nodes between first and second terminals; a second voltage divider coupled between the output terminal and the second terminal, and having a third node between the output terminal and the second terminal; a first transistor having a first control electrode connected to the third node, and a first conduction path connected between the second node and the second terminal; a capacitor connected between the first node and the second terminal; first and second resistors; a second transistor having a second control electrode and having a second conduction path connected in series with the first resistor between the first node and the second terminal; Zener diode connected in series with the second resistor across the capacitor with a junction therebetween being coupled to the second control electrode; an output transistor having a third control electrode, and a conduction path connected between the second terminal and the output terminal; a third resistor connected between the third control electrode and another junction between the first resistor and the second transistor; and a relay having a coil connected between the first terminal and the output terminal, and having a set of contacts through which electric current flows to control the dc series motor. - View Dependent Claims (15, 16, 17)
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18. A method for controlling a motor of a crane that receives voltage from a power supply, said motor comprising the steps of:
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detecting whether the voltage from a power supply exceeds a threshold level in which event a sensor signal is produced, wherein the threshold level is greater than a voltage produced by the motor operating in a regenerative mode during interruption of the voltage from the power supply; responding to the sensor signal by operating a switch through which electric current flows to control the motor; and operating a mechanical brake when the electric current ceases to flow through the switch wherein operation of the mechanical brake stops movement of a member driven by the motor.
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Specification