Electronic emergency-stop braking circuit for robotic arms
Representative embodiments of a system for braking a cyclically rotating motor upon a power failure include (i) charge-storage circuitry for storing charge and converting the stored charge to an output voltage upon power failure; (ii) one or more passive electrical elements for conducting current induced by motor rotations; and (iii) voltage-actuated circuitry connected to the passive electrical element and the charge-storage circuitry for braking the motor during each half-cycle of motor rotation. The circuitry is inactive until actuated by the charge-storage circuitry upon power failure.
1. An unpowered braking system for braking a cyclically rotating motor, the system comprising:
at least one passive electrical element for conducting current induced by motor rotations without activating a bridge circuit powering the motor; and
charge-storage means, connected to said at least one passive electrical element, for storing charge and converting the stored charge to an output voltage;
voltage-actuated circuitry for braking the motor upon activation by a braking voltage; and
control circuitry for controlling activation and deactivation of the voltage-actuated circuitry, the control circuitry being (i) connected to the charge-storage circuitry to receive the output voltage therefrom and (ii) responsive to a braking signal to boost a voltage at the voltage-actuated circuitry from a non-braking voltage to the braking voltage.
2. The system of claim 1 , wherein the voltage-actuated circuitry is connected across a motor winding and brakes the motor by short-circuiting the motor winding by causing current to flow therethrough.
3. The system of claim 1 , further comprising a bridge circuit that itself comprises a plurality of transistors.
4. The system of claim 1 , further comprising a logic gate to control activation and deactivation of the voltage-actuated circuitry.
5. The system of claim 4 , wherein the logic gate is regulated by at least one of a controller or a signal indicating a power status.
6. The system of claim 5 , wherein the voltage-actuated circuitry is activated when an output of the logic gate is below a predetermined minimum voltage threshold.
7. The system of claim 5 , wherein the voltage-actuated circuitry is deactivated when an output of the logic gate is above a predetermined maximum voltage threshold.
8. The system of claim 1 , wherein the charge-storage circuitry comprises a capacitor.
9. The system of claim 1 , wherein the passive electrical element comprises a diode.
10. The system of claim 1 , wherein the voltage-actuated circuitry comprises a transistor.
11. The system of claim 1 , wherein the voltage-actuated circuitry is activated each half-cycle of motor rotation.
12. The system of claim 1 , wherein the voltage-actuated circuitry is activated at a full-duty cycle of motor rotation.
13. The system of claim 1 , wherein the charge-storage circuitry comprises a zener diode having a breakdown voltage threshold and at least one transistor, wherein the at least one transistor is inactive until actuated by a sufficient voltage above the zener breakdown threshold voltage.
14. A method of generating motor braking, the method comprising:
storing charge in a charge-storage element, storage charge means connected to at least one passive electrical element, for storing charge and converting the stored charge to an output voltage;
converting, by the charge-storage element, the stored charge to an output; and
absent a braking signal, applying the output from the charge-storage element to voltage-actuated braking circuitry at a voltage level insufficient to cause braking and, upon assertion of the braking signal, causing the output from the charge-storage element to be applied to the braking circuitry at a braking level to cause braking of the motor.
15. The method of claim 14 , wherein the braking circuitry is connected across a motor winding and brakes the motor by causing current to flow through the motor winding, the motor winding being short-circuited each half-cycle of motor rotation.
16. The method of claim 14 , wherein the braking circuitry is connected across a motor winding and brakes the motor by causing current to flow through the motor winding, the motor winding being short-circuited at a full-duty cycle of motor rotation.
17. The method of claim 14 , wherein the braking circuitry is connected across a motor winding and brakes the motor by causing current to flow through the motor winding, the motor winding being short-circuited when a speed of motor rotation is above a threshold value.