Dual Loop Robot Control for Gear Compliance
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Solution Overview
Problem
Existing robot control systems face challenges in achieving high accuracy, particularly due to compliance errors in the gear train, and struggle with handling interactions between robot axes using single or pure secondary encoder position control, which limits motion speed and responsiveness.
Innovation Solution
Implementing a dual position loop control system where the primary encoder on the motor provides traditional position control, and the secondary encoder on the output side of the gear train generates a compensation signal to enhance accuracy, allowing for higher speed motion and dynamic position control even during axis interactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pure secondary encoder position control is used, then measurement precision is improved, but device complexity increases and ease of operation deteriorates due to difficulty in handling axis interactions
Solution Approach 1:
The control system is segmented into two independent position loops: an outer loop using secondary encoders for high-precision position measurement and an inner loop using primary encoders for velocity control. This segmentation allows each loop to specialize in its function, improving position measurement accuracy while maintaining operational simplicity through modular architecture.
Solution Approach 2:
The primary encoder acts as an intermediary between the secondary encoder and the servo motor. The outer position loop generates position commands based on secondary encoder feedback, which are then processed by the inner velocity loop using primary encoder feedback to generate motor control signals. This intermediary structure simplifies handling of axis interactions.
2Manufacturing precision
If secondary encoder is used for position control, then manufacturing precision is improved, but speed and responsiveness deteriorate due to lack of closed loop integration
Solution Approach 1:
The system implements closed-loop feedback control with two position loops. The outer loop continuously monitors position using the secondary encoder and generates corrective position commands. The inner loop uses primary encoder velocity feedback to achieve the commanded position dynamically. This dual feedback structure maintains high positioning accuracy while enabling fast response and high-speed motion.
Solution Approach 2:
The control system dynamically switches between position control modes. The outer loop provides precise position control when accuracy is critical, while the inner velocity loop enables dynamic high-speed motion. The layered architecture allows the system to adapt its control characteristics in real-time based on operational requirements.
3Device complexity
If single position loop control is used, then device complexity is reduced, but manufacturing precision deteriorates due to compliance errors in gear train
Solution Approach 1:
The secondary encoder mounted on the output side of the gear train acts as an intermediary measurement device that directly measures the actual position at the tool flange, bypassing the compliance errors of the gear train. This intermediary measurement, combined with the dual-loop control structure, achieves high precision without requiring overly complex single-loop control.
Solution Approach 2:
The system adds a second position loop dimension to the control architecture. Instead of relying on a single complex control loop, the patent introduces an outer position loop that operates in addition to the inner velocity loop. This dimensional expansion of the control structure enables high precision by compensating for gear train compliance errors that a single loop cannot address.
4Speed
If secondary encoder is integrated into closed loop system, then speed and responsiveness are improved, but device complexity increases
Solution Approach 1:
The control system is divided into distinct functional segments: the outer position loop handles position accuracy using secondary encoder feedback, while the inner velocity loop handles dynamic response using primary encoder feedback. This segmentation enables high-speed responsive motion while keeping each control module relatively simple and manageable.
Solution Approach 2:
The patent merges two encoder systems into a unified dual-loop control architecture. The outer loop combines secondary encoder position feedback with the inner loop's primary encoder velocity feedback to create a coordinated control system. This merging achieves high-speed responsiveness and accuracy while distributing complexity across two complementary loops rather than requiring one overly complex single loop.
Data Source
AI summary
A method of and apparatus for achieving dynamic robot accuracy includes a control system utilizing a dual position loop control. An outer position loop uses secondary encoders on the output side of the gear train of a robot joint axis, while the inner position loop uses the primary encoder attached to the motor. Both single and dual loop control can be used on the same robot and tooling axes.