Impact Tool Phase Control for Fastener Torque and Load Drop Detection
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Solution Overview
Problem
Impact tools, such as impact drivers and wrenches, often face challenges in accurately controlling power delivery to prevent overdriving or stripping of fasteners, as they can either apply too much power, leading to damage, or insufficient power, resulting in slow installation and inadequate torque.
Innovation Solution
The implementation of a brushless motor system with a controller that switches between open loop and closed loop control based on predefined threshold values for motor parameters like speed and torque, allowing for selective application of rotational impacts and optimizing power delivery for different fastening tasks, including modes for hard and soft joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If impact tools are used at full power, then the torque and speed of fastener installation is improved, but the fasteners may be overdriven or stripped
Solution Approach 1:
The controller dynamically switches between open loop and closed loop control modes based on real-time motor parameter feedback. When motor speed or torque exceeds a threshold, the system transitions to closed loop control to precisely regulate power delivery, preventing fastener damage while maintaining high torque capability when needed.
Solution Approach 2:
The closed loop control mode continuously monitors motor parameters (speed or torque) and adjusts power delivery accordingly. This feedback mechanism allows the system to detect when fastener resistance increases and automatically reduce power to prevent overdriving or stripping, while still delivering full power when the fastener is being properly installed.
2Reliability
If impact tools are used at less than full power, then the fastener damage is prevented, but the speed of application becomes too slow
Solution Approach 1:
The system dynamically adjusts power delivery based on real-time conditions rather than operating at a fixed power level. During initial fastener installation, the tool operates at full power for rapid installation. When fastener resistance increases and approaches the threshold, the system smoothly transitions to closed loop control to maintain optimal torque without excessive speed reduction, thus balancing productivity and reliability.
Solution Approach 2:
The controller changes operational parameters (control mode, power level) based on detected conditions. By monitoring motor parameters and switching between control modes, the system optimizes the balance between installation speed and fastener protection, delivering high power when appropriate and precisely controlling power when near the damage threshold.
3Measurement precision
If closed loop control is used throughout operation, then the precision of power delivery is improved, but the complexity of the control system increases
Solution Approach 1:
The control operation is segmented into distinct phases: open loop control for the initial high-power installation phase, and closed loop control for the precision regulation phase when approaching the threshold. This segmentation allows the system to use simple open loop control when precision is less critical, reducing overall system complexity while maintaining precision when needed.
Solution Approach 2:
The control system dynamically selects the appropriate control mode based on operating conditions rather than using closed loop control continuously. This dynamic switching reduces complexity by enabling open loop control during periods when precise regulation is unnecessary, while still providing closed loop precision control when the system approaches critical thresholds.
Data Source
AI summary
An impact power tool includes a motor, a controller, and an impact mechanism configured to rotationally drive an output spindle. The controller is configured to control power delivered to the motor, during a third phase of operation after a second phase of operation and starting upon expiration of a predetermined time period. The third phase has one or more of a third non-zero target rotational speed, a third duty cycle setting, a third conduction band setting, or a third advance angle setting. The controller is configured to control power delivered to the motor, during a fourth phase of operation after the third phase upon detection of a reduction in load on the output spindle or cessation of impacting. The fourth phase has one or more of a fourth non-zero target rotational speed, a fourth duty cycle setting, a fourth conduction band setting, or a fourth advance angle setting.