QDD Wearable Robot Control Without Torque Sensors
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Solution Overview
Problem
Wearable robots face challenges in achieving high accuracy and stability without torque sensors, particularly due to the limitations of conventional actuators like series elastic actuators (SEA) which require additional components, are costly, and cause human-robot interaction instability due to non-collocated sensing issues.
Innovation Solution
A collocated impedance control method using proprioceptive quasi-direct drive (QDD) actuators that estimates torque without a torque sensor, improving stability and reducing the need for costly and bulky sensors, enabling lightweight and cost-effective wearable robots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If series elastic actuators are used to estimate output torque via elastic element deflection, then torque estimation accuracy is improved, but device complexity and mass increase due to additional springs and components
Solution Approach 1:
The patent extracts and removes the torque sensor and elastic element from the actuator structure. Instead of using traditional SEA components to estimate torque, the invention uses a simplified actuator model that calculates torque directly from motor current and gear ratio, eliminating the need for physical torque sensing components while maintaining estimation accuracy.
Solution Approach 2:
The patent replaces the mechanical torque estimation system (using elastic elements and deflection measurement) with an electrical-based calculation system. Torque is estimated through electrical current measurements and mathematical modeling of the motor-gear system, substituting mechanical sensing with electrical sensing and computational estimation.
2Measurement precision
If torque sensors are used in conventional actuators to command torque accurately, then torque control accuracy is improved, but device cost and mass increase
Solution Approach 1:
The patent removes the torque sensor from the actuator system entirely. Instead of physically measuring torque with a sensor, the system estimates torque through mathematical calculation based on motor current and known gear parameters, eliminating the heavy sensor component while maintaining control accuracy.
Solution Approach 2:
The patent creates a virtual model or mathematical copy of the torque sensing function. Rather than using a physical sensor to measure torque, the system uses a computational model that replicates torque estimation based on electrical measurements, achieving the same functional outcome without the physical hardware.
3Loss of information
If exteroceptive sensory feedback is used in actuator paradigms, then sensing capability is improved, but human-robot interaction stability deteriorates due to non-collocated sensing problems upon collision
Solution Approach 1:
The patent inverts the traditional sensing approach by using proprioceptive feedback (sensing at the actuator location) instead of exteroceptive feedback (sensing at the interaction point). This reversal places the sensor and actuator in the same location, eliminating non-collocated sensing problems and improving interaction stability while maintaining full sensing capability through the mathematical model.
Data Source
AI summary
Various examples are provided related to control of a wearable robot without torque sensors. In one example, a method includes generating a control signal for a quasi-direct-drive (QDD) actuator of the wearable robot and adjusting operation of the QDD actuator based upon the control signal. The control signal can be determined by a collocated controller using current and angle of rotation of the QDD actuator and a reference trajectory angle. In another example, a wearable robot includes a support structure that can interface with a user; a quasi-direct-drive (QDD) actuator coupled to the support structure; and processing circuitry that can generate a control signal for the QDD actuator, the control signal determined by a collocated controller based upon current and angle of rotation of the QDD actuator and a reference trajectory angle and adjust operation of the QDD actuator based upon the control signal.