Servomotor DC Link Braking for Safe Emergency Stops
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Solution Overview
Problem
Current methods for controlling servomotors in industrial robots lack effective and safe braking mechanisms, particularly in scenarios requiring rapid speed reduction or emergency stops, where mechanical brakes may not be feasible or efficient.
Innovation Solution
A method utilizing a frequency converter with a direct-voltage DC link, a first switching device to disconnect from the electrical grid, and a second switching device to control the servomotor, enabling regenerative or short-circuit braking through controllable power semiconductor switches, allowing for controlled speed reduction without mechanical brakes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If regenerative braking is used to reduce servomotor speed, then energy is recovered and braking efficiency is improved, but electrical current may continue to flow from the grid through the DC link creating safety hazards
Solution Approach 1:
The system continuously monitors the current flowing through the DC link during braking operations. When regenerative braking causes current to flow back into the DC link, the monitoring device detects this condition and triggers a warning signal to the control device, which can then take corrective action to prevent unsafe conditions.
Solution Approach 2:
A monitoring device is introduced as an intermediary between the braking system and the control system. This device specifically monitors the DC link current condition and communicates with the control device, enabling the system to detect and respond to unsafe regenerative braking conditions without requiring direct complex control logic in the main controller.
2Reliability
If the first switching device is switched off to disconnect from the electrical grid, then safety is improved by preventing grid energy from reaching the DC link, but the servomotor may not be braked effectively if current monitoring is not performed
Solution Approach 1:
The system performs preliminary current monitoring of the DC link before and during the switching off operation. By monitoring the current condition in advance and during the transition, the system ensures that regenerative braking is properly executed and that the servomotor speed is reduced safely even after grid disconnection.
Solution Approach 2:
The monitoring device provides continuous feedback on the DC link current status, allowing the control system to verify that grid disconnection has been effective and that the servomotor braking is proceeding as intended, enabling corrective actions if braking performance is insufficient.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides a safe and efficient means to control servomotor speed, enabling rapid braking and emergency stops by electrically managing the servomotor's energy flow, enhancing safety and operational efficiency in industrial robot applications.
Implementation Method 1
at least one inverter circuit which can be fed from the direct-voltage DC link and has controllable power semiconductor switches for electrically controlling the servomotor
Implementation Method 2
a first switching device which is designed, in its switched-on state, to feed the direct-voltage DC link with electrical energy from the input circuit and, in its switched-off state, to prevent a feed of the direct-voltage DC link from the electrical grid
Implementation Method 3
a second switching device which is designed, in its switched-on state, to feed the servomotor with electrical energy from the inverter circuit in order to drive the servomotor, and, in its switched-off state, to prevent driving of the servomotor
Data Source
AI summary
A method for controlling a servomotor with a converter includes monitoring a circuit of a direct-voltage DC link that is connected to an input circuit for flow of an electric current; switching off a first switching device to end the supply of the direct-voltage DC link from an electrical grid if a stop signal occurs; braking the servomotor by control of power semiconductor switches of an inverter circuit in a regenerative braking operation, to reduce the rotation speed of the servomotor, if the monitoring detects that an electric current is not flowing after the first switching device has been switched off; and switching off a second switching device to prevent feeding electrical energy from the direct-voltage DC link into the servomotor if the monitoring detects a flow of electric current after the first switching device has been switched off.