Torque Control Device for Screw Tightening
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Solution Overview
Problem
Existing torque control devices face challenges in accurately controlling torsional torque in screw tightening applications, particularly in preventing overshoot and ensuring precise torque application amidst variations in friction and mechanical transmission inefficiencies.
Innovation Solution
A torque control device comprising a controller that generates references for two motors to synchronize and control their rotational speeds according to specific profiles, producing and managing torsional torque through coordinated acceleration and deceleration, and optionally using phase differences between motors to achieve precise torque control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If current limiting control is used to prevent overshoot of tightening torque, then tightening torque accuracy is improved, but response time increases due to gradual current increase
Solution Approach 1:
The patent applies dynamic control by switching between different control modes (current limiting control and constant acceleration control) based on real-time motor state. The controller dynamically adjusts the current reference value trajectory: initially using current limiting control to prevent overshoot, then transitioning to constant acceleration control to improve response time, thereby resolving the contradiction between torque accuracy and response time.
Solution Approach 2:
The patent changes the control parameter (current reference value) based on motor rotational speed and torque state. By monitoring motor state and adjusting the current reference value trajectory accordingly, the system achieves both accurate torque control and fast response. The parameter change strategy includes using different control algorithms at different stages of motor operation.
2Manufacturing precision
If synchronous acceleration of two motors is used to eliminate static friction influence, then torque control accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges the control of two motors into a unified control system that generates coordinated reference values for both motors. By synchronizing the acceleration phases of both motors and using a unified control algorithm that accounts for static friction elimination, the system achieves improved torque control accuracy while managing complexity through integration rather than separate control mechanisms.
3Productivity
If motor rotational speed is varied to produce torsional torque, then torque application efficiency is improved, but torque precision deteriorates due to speed fluctuations
Solution Approach 1:
The patent implements feedback control by monitoring motor rotational speed and using this information to adjust the current reference value. The controller detects speed fluctuations and compensates for them by adjusting control parameters, thereby maintaining torque precision even when motor speed varies to produce torsional torque. This feedback mechanism resolves the contradiction between efficiency and precision.
Data Source
AI summary
A torque control device controlling torque of first and second mechanical units connected coaxially to each other through connecting members includes a controller generating first and second references from a command from a host system, first and second motors respectively driving the first and second mechanical units, first and second motor control units respectively controlling the first and second motors on the basis of the first and second references. The first and second references synchronously accelerate the first and second motors to first rotational speed, then increase rotational speed of the second motor according to a speed profile to produce torsional torque in the connecting members, decelerate the second motor to the first rotational speed after the torsional torque reaches a predetermined value, and synchronously decelerate and stop the first and second motors after a predetermined time period elapses.