Stepper Motor Driving Mechanism for High Backdrivability
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Solution Overview
Problem
Traditional robotic joints have limitations in backdrivability, bandwidth, and variable elastic behavior, making them inadequate for tasks requiring rapid force control and adaptability, such as walking robots experiencing repetitive impacts.
Innovation Solution
A driving mechanism utilizing a stepper motor with a low transmission ratio and a local controller to achieve programmable, real-time torque characteristics, enabling high backdrivability, high bandwidth force control, and variable elastic behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a high transmission ratio is used in robotic joints to achieve high torque, then the torque capability is improved, but the moment of inertia increases and backdrivability deteriorates
Solution Approach 1:
The patent replaces traditional mechanical friction-based braking systems with an electric braking system using a brake motor. The brake motor provides electromagnetic braking force that can be precisely controlled, eliminating the need for high transmission ratios to achieve torque control. This substitution allows the system to maintain high backdrivability while achieving the required torque through controlled electromagnetic forces rather than mechanical gear multiplication.
2Force
If a high transmission ratio is used in robotic joints to achieve high torque, then the torque capability is improved, but the reaction speed to sudden movements deteriorates
Solution Approach 1:
The patent replaces mechanical transmission systems with high inertia gears with a direct-drive brake motor system. The electromagnetic braking and driving forces can be rapidly modulated without the inertial delays inherent in high-ratio mechanical transmissions. This allows the robotic joint to respond quickly to sudden movement commands while maintaining the necessary torque output through controlled electromagnetic forces.
3Reliability
If elastic members are inserted to increase shock tolerance, then the shock tolerance is improved, but the system complexity and control bandwidth limitations increase
Solution Approach 1:
The patent replaces passive elastic members (springs) with an active electromagnetic braking system that can dynamically adjust to shock loads. The brake motor's electromagnetic forces can be rapidly modulated to absorb and dissipate shock energy, providing shock tolerance equivalent to or better than mechanical springs without the associated complexity of elastic member integration and the bandwidth limitations of passive elastic systems.
4Adaptability or versatility
If elastic members are inserted to enable variable stiffness, then the adaptability is improved, but the control bandwidth is limited by low-speed force control
Solution Approach 1:
The patent replaces passive elastic members that require slow force control with an active electromagnetic braking system. The electromagnetic forces can be rapidly adjusted through electronic control, enabling variable stiffness characteristics with high control bandwidth. The brake motor can dynamically modulate braking forces to achieve the desired stiffness at any moment, responding quickly to control signals without the bandwidth limitations of mechanical elastic systems.
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
The solution provides a robotic joint with over 90% backdrivability, efficient force control, and adjustable elastic behavior, enhancing the robotic joint's ability to react to impacts and simulate various elastic conditions, improving energy efficiency and natural movement patterns.
Implementation Method 1
a driving mechanism, which comprises a stepper motor (12) for driving the driving mechanism
Implementation Method 2
the motor shaft (14) of the stepper motor (12) is connected to the drive shaft (10) by means of a transmission (54)
Data Source
AI summary
The invention is a driving mechanism for exerting a pre-determined torque characteristic, comprising a stepper motor (12) having a motor shaft, a rotation measuring device detecting the angular position of the motor shaft (14), a motor control unit effecting the torque characteristic on the basis of the angular position of the motor shaft (14), a drive shaft (10) exerting the torque characteristic and an essentially backlash-free transmission connecting the drive shaft (10) with the motor shaft (14), and the motor control unit is a local motor control unit providing operating signals to the stepper motor (12) and being programmable in at least one parameter.