Impact Tool Control Modes for Fastener Overdrive Prevention
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Solution Overview
Problem
Impact drivers and impact wrenches often overdrive fasteners, stripping their heads or threads when used at full power, or apply too slowly when used at less than full power, failing to achieve desired torque.
Innovation Solution
An impact power tool with a brushless motor controlled by a controller that switches between open loop and closed loop control modes based on motor parameters, adjusting conduction band and advance angle values to optimize torque and prevent overdriving or underdriving.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the impact tool is used at full power, then the fastening speed and torque are improved, but the fastener heads or threads are stripped causing overdriving
Solution Approach 1:
The patent implements dynamic control by switching between open-loop and closed-loop control modes based on motor parameter thresholds. The controller monitors motor parameters (such as current, speed, or torque) and transitions from open-loop control (for high-speed operation) to closed-loop control (for precise torque control) when thresholds are exceeded. This dynamic adaptation allows the system to operate at full power when safe, while automatically preventing overdriving when approaching dangerous parameters.
Solution Approach 2:
The patent employs feedback control through closed-loop control mode that continuously monitors motor parameters and adjusts power delivery accordingly. When motor parameters exceed predetermined thresholds, the closed-loop system provides real-time feedback to the controller, which then modulates power to the motor to maintain safe operating parameters. This feedback mechanism prevents fastener damage by automatically reducing power before damage occurs, while still allowing high-speed operation during safe conditions.
2Object-affected harmful factors
If the impact tool is used at less than full power, then fastener damage is prevented, but the application speed becomes too slow and desired torque is not achieved
Solution Approach 1:
The system dynamically adjusts control mode based on real-time motor parameters. During normal operation below threshold parameters, the system operates in open-loop mode delivering full power for maximum speed. When parameters approach thresholds that could cause overdriving, the system dynamically transitions to closed-loop mode, which modulates power delivery to maintain safe operating parameters while continuing to drive the fastener efficiently. This dynamic switching ensures both high productivity and fastener protection.
Solution Approach 2:
The patent changes control parameters (control mode, power level) based on motor parameter thresholds. The controller monitors motor parameters such as current, speed, or torque and changes the control strategy accordingly - using open-loop control with high power for most of the fastening process to maintain speed, and switching to closed-loop control with adjusted power parameters only when thresholds indicate approaching overdrive conditions. This selective parameter change optimizes both speed and safety.
3Speed
If open loop control is used for the entire operation, then the application speed is maintained, but the torque control precision deteriorates causing potential overdriving
Solution Approach 1:
The patent implements a dynamic control strategy that switches between open-loop and closed-loop modes based on motor parameter thresholds. During the majority of the fastening operation, when motor parameters are well below thresholds, the system uses open-loop control to maintain high application speed. When motor parameters approach thresholds indicating nearing of maximum torque capacity, the system dynamically transitions to closed-loop control, which provides precise torque control to prevent overdriving. This dynamic mode switching optimizes both speed and precision at different stages of operation.
Solution Approach 2:
The patent segments the control process into two distinct phases: an open-loop phase for high-speed operation when parameters are low, and a closed-loop phase for precise torque control when parameters approach thresholds. The controller divides the fastening operation into these segments based on real-time parameter monitoring, using open-loop control for the initial and middle portions of fastening where speed is critical, and switching to closed-loop control for the final portion where precision is critical to prevent overdriving. This segmentation allows each control mode to operate in its optimal performance range.
4Manufacturing precision
If closed loop control is used for the entire operation, then torque control precision is improved, but the application speed decreases due to continuous parameter monitoring and adjustment
Solution Approach 1:
The patent implements a dynamic control strategy that activates closed-loop control only when motor parameters approach predetermined thresholds, rather than maintaining it continuously. During normal operation when parameters are well below thresholds, the system uses open-loop control for maximum speed. Closed-loop control is dynamically activated only in the critical region near threshold parameters where precise torque control is needed to prevent overdriving. This dynamic activation minimizes the time spent in lower-speed closed-loop mode while ensuring precision when absolutely necessary.
Solution Approach 2:
The patent applies closed-loop control partially rather than continuously - specifically, only when motor parameters exceed predetermined thresholds. This partial application of closed-loop control provides sufficient torque precision to prevent overdriving during the critical final portion of fastening, while allowing open-loop high-speed operation during the majority of the fastening process. This partial action approach achieves the necessary precision without the continuous speed penalty of full closed-loop operation.
Data Source
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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.