Robot Motor Control for Low-Temperature Friction Reduction
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Solution Overview
Problem
Existing robot control methods fail to effectively reduce viscous friction of grease in reduction gears at low temperatures without risking motor demagnetization or causing wrong overload detection, leading to insufficient torque and potential robot shutdown.
Innovation Solution
A robot control method that adds d-axis electric current only when the absolute value of the motor electric current command is within predetermined limits and the detected overload is below a certain threshold, ensuring the motor generates heat to reduce friction without exceeding the allowable electric current or causing demagnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If d-axis electric current is added to reduce viscous friction of grease at low temperature, then viscous friction decreases, but apparent electric current may exceed allowable maximum value causing magnet demagnetization
Solution Approach 1:
The patent changes the control parameters by selectively adding d-axis electric current only when temperature is below a predetermined threshold and current conditions are satisfied. This conditional parameter change allows the system to reduce viscous friction at low temperatures while preventing magnet demagnetization by avoiding excessive current addition when temperature is not low.
Solution Approach 2:
The patent implements dynamic control of d-axis electric current addition based on real-time temperature and current conditions. The control amount is adjusted dynamically according to the motor electric current command and temperature, allowing the system to adapt to changing operating conditions and prevent both insufficient friction reduction and magnet demagnetization.
2Object-affected harmful factors
If d-axis electric current is added to generate heat and reduce friction, then viscous friction decreases, but apparent electric current increases causing wrong overload detection and robot stop
Solution Approach 1:
The patent introduces temperature as a new control parameter to determine whether to add d-axis electric current. By changing the control logic to include temperature-based conditional parameter adjustment, the system can distinguish between low-temperature friction increase (requiring current addition) and normal operation (where current addition would cause false overload detection).
Solution Approach 2:
The patent implements dynamic conditional control where the d-axis current addition is enabled only when specific conditions (temperature below threshold and current magnitude within limits) are met. This dynamic control prevents wrong overload detection by avoiding unnecessary current addition during normal operating conditions while still providing friction reduction when needed.
3Force
If q-axis electric current is used to generate torque, then driving torque is sufficient, but viscous friction of grease increases at low temperature
Solution Approach 1:
The patent segments the electric current control into two independent components: q-axis current for torque generation and d-axis current for heat generation. By separating these functions and controlling them independently based on different conditions, the system can maintain sufficient driving torque through q-axis current while adding d-axis current only when low temperature requires friction reduction.
Solution Approach 2:
The patent implements dynamic switching between pure torque control (q-axis only) and combined control (q-axis plus d-axis) based on temperature conditions. When temperature is above the threshold, only q-axis current is used for torque. When temperature drops below the threshold and current conditions are met, d-axis current is dynamically added to generate heat and reduce friction while maintaining torque capability.
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 effectively decreases viscous friction of grease at low temperatures without demagnetizing the motor and prevents wrong overload detection, ensuring continuous robot operation by maintaining the apparent electric current within safe limits.
Implementation Method 1
d-axis electric current is added... Consequently, the motors generate heat, and thus viscous friction of grease for reduction gears decreases
Data Source
AI summary
A robot control method of controlling motion of a robot arm by using a servo motor includes adding d-axis electric current to a motor electric current command (steps 15-6, 15-8) if external temperature is less than or equal to a predetermined value (step 15-3), and if an absolute value of the motor electric current command is less than or equal to a predetermined value (step 15-4), and if a value of detected overload is less than or equal to a predetermined value (step 15-5).