Servo Motor Braking Control With Dynamic DC Link Thresholds
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Solution Overview
Problem
Existing methods for braking control of servomotors in industrial robots are not effective and safe, particularly in emergency situations where mechanical separation or braking is not possible, and they lack efficient energy management during regenerative braking.
Innovation Solution
A method using a frequency converter with a rectifier circuit connected to an alternating voltage network, a DC intermediate circuit with a capacitor and a brake chopper, and controllable power semiconductor switches, where regenerative braking is achieved by dynamically controlling the switch-on and switch-off thresholds of the brake chopper based on the servo motor's speed, allowing for controlled reduction of speed without mechanical brakes and minimizing energy storage to prevent unintended restarts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If regenerative braking is used to reduce speed without mechanical brakes, then energy efficiency is improved, but the risk of unintended motor restarts increases due to energy stored in the intermediate circuit capacitor
Solution Approach 1:
The patent applies dynamics by making the switch-on and switch-off thresholds of the brake chopper dynamically adjustable during regenerative braking based on the current speed of the servo motor. This allows the braking resistance to be adaptively controlled - higher thresholds at higher speeds for effective braking, and lower thresholds at lower speeds to dissipate remaining energy and prevent unintended restarts, thus resolving the contradiction between energy efficiency and safety
Solution Approach 2:
The patent changes the voltage thresholds parameter of the brake chopper during the braking process. By dynamically adjusting the switch-on and switch-off thresholds based on motor speed, the system optimizes energy dissipation at different braking stages, ensuring both efficient regenerative braking and prevention of unintended restarts by dissipating residual energy in the capacitor
2Speed
If the brake chopper switches on at high DC link voltage to maximize braking effectiveness, then braking performance is improved, but energy is wasted in the braking resistor
Solution Approach 1:
The patent makes the brake chopper thresholds dynamic rather than fixed. During high-speed braking, higher thresholds enable effective braking performance. As speed decreases, the thresholds are automatically reduced to minimize energy dissipation while still preventing unintended restarts. This dynamic adjustment resolves the contradiction by optimizing the balance between braking performance and energy loss at different operating stages
3Reliability
If the intermediate circuit voltage is maintained at a high level to ensure sufficient energy for inverter operation, then system reliability is improved, but the risk of unintended motor restarts increases
Solution Approach 1:
The patent dynamically adjusts the voltage thresholds based on motor speed during braking. At higher speeds, higher voltage levels are maintained to ensure sufficient energy for reliable inverter operation. As the motor slows down, the thresholds are reduced to dissipate excess energy and prevent unintended restarts, thus resolving the contradiction between maintaining system reliability and preventing harmful restarts
Solution Approach 2:
The patent applies preliminary action by proactively controlling the brake chopper thresholds during the braking process to prevent unintended restarts before they can occur. By dynamically lowering thresholds as speed decreases, the system preemptively dissipates energy that could cause harmful restarts, while still maintaining sufficient voltage for reliable operation during the braking transient
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 method enables safe and effective braking of servomotors by actively controlling regenerative braking, reducing the risk of unintended motor restarts and ensuring compliance with safety standards like Safe Torque Off, while optimizing energy usage during the braking process.
Implementation Method 1
the servomotor (M) is braked exclusively by means of active control of the power semiconductor switches (S1 to S6) in a generator braking mode
Implementation Method 2
the braking resistor (R6) is connected and disconnected via a braking chopper (S7)
Data Source
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AI summary
The invention relates to a method for controlling at least one servomotor (M, M1-M6) in a braking manner by means of a frequency converter (1) which comprises a rectifier circuit (3) connectable to an electric alternating-voltage network (2), a direct-voltage intermediate circuit (4), which is fed from the electric alternating-voltage network (2) in the state connected to the electric alternating-voltage network (2) and has an intermediate-circuit capacitor (5) and has a brake resistor (6), which can be connected and disconnected via a brake chopper (S7) of the direct-voltage intermediate circuit (4), and at least one inverter circuit (7), which is fed from the direct-voltage intermediate circuit (4) and has controllable semiconductor switches (S1-S6). The invention also relates to a correspondingly designed robot (8) and an associated computer program product.