Brushless Impact Tool Control for Precise Fastener Torque
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Solution Overview
Problem
Impact tools, such as impact drivers and wrenches, often face challenges in accurately delivering torque to fasteners, leading to overdriving or stripping when used at full power, and inefficiency when used at reduced power, as they may apply torque too slowly or fail to achieve desired torque levels.
Innovation Solution
A brushless impact power tool with a controller that switches between open loop and closed loop control based on motor parameters, using a threshold value to optimize power delivery, and includes a mode switch for selecting operation modes suited for hard or soft joints, and features to prevent over-tightening or over-loosening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If impact tools are used at full power, then torque delivery speed is improved, but fastener damage (overdriving or stripping) occurs
Solution Approach 1:
The controller continuously monitors motor parameters (current, speed, torque) and adjusts power delivery in real-time based on feedback signals. When the fastener reaches proper tightness, the increased load is detected and the controller automatically reduces power to prevent overdriving or stripping, while maintaining high speed during the initial fastening phase
Solution Approach 2:
The system dynamically transitions between open-loop and closed-loop control modes, and adjusts motor parameters (conduction band, advance angle) in real-time based on operating conditions. This dynamic adaptation allows the tool to operate at full power when the fastener needs rapid installation, then smoothly transition to controlled power delivery when approaching the target torque to prevent damage
2Object-affected harmful factors
If impact tools are used at reduced power, then fastener damage is prevented, but application speed becomes too slow or desired torque is not achieved
Solution Approach 1:
The controller dynamically adjusts motor parameters including conduction band and advance angle values based on real-time motor performance. During closed-loop control, these parameters are increased as torque on the output spindle increases, allowing the system to maintain high speed while approaching the target torque, and only reduce power when necessary to prevent fastener damage
Solution Approach 2:
The system changes motor operating parameters (conduction band, advance angle, current limits) based on the operational phase and detected conditions. The threshold value for switching between control modes is optimized for impacting operation, allowing the tool to maintain high performance while preventing damage through parameter optimization rather than simply reducing power
3Device complexity
If open loop control is used, then device complexity is reduced, but torque precision deteriorates
Solution Approach 1:
The control process is segmented into distinct phases: open-loop control for initial motor operation and transition phase, then closed-loop control for precision torque delivery. This segmentation allows the system to use simple open-loop control when precision is less critical, then switch to precise closed-loop control when torque accuracy is paramount, optimizing both complexity and precision
4Measurement precision
If closed loop control is used, then torque precision is improved, but device complexity increases
Solution Approach 1:
The system dynamically transitions between open-loop and closed-loop control modes based on operational needs. Closed-loop control with feedback is activated when precision torque delivery is required (during impacting operation), while open-loop control handles less critical phases. This dynamic switching reduces overall system complexity while maintaining high torque precision when needed
Solution Approach 2:
The controller optimizes motor parameters (conduction band, advance angle) during closed-loop operation to maximize torque precision. By carefully selecting and adjusting these parameters, the system achieves precise torque control with minimal additional complexity, as the parameter optimization works synergistically with the feedback control mechanism
Data Source
AI summary
A power tool includes a housing, a brushless motor received in the housing, a power switch coupled to the housing and actuatable by a user, a controller configured to control power delivery to the motor in response to actuation of the power switch, and an output spindle configured to rotate when the motor is energized. The controller is configured to maintain an amount of current delivered to the motor to be less than or equal to a current limit by turning off or reducing power to the motor for a time period if the current exceeds the current limit and then restarting power delivery to the motor. The time period is greater than the duration of one full current cycle.