Power Tool Motor Duty Cycle Control for Torque Management
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Solution Overview
Problem
High-output brushless DC motors in power tools often lead to excessive torque and temperature increases during continuous operation, potentially damaging screw heads and limiting lifespan, especially when the motor output exceeds necessary fastening requirements.
Innovation Solution
Implementing a control method that dynamically adjusts the duty ratio of the motor based on current detection, switching from high to low duty ratio when thresholds are exceeded, and using multiple operation modes to manage torque and prevent excessive load, thereby protecting the motor and fastening components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high-output brushless DC motor is used to increase rotational speed and fastening torque, then productivity and fastening speed are improved, but temperature increase and mechanical stress during continuous operation worsen, potentially damaging screw heads and limiting lifespan
Solution Approach 1:
The patent applies dynamics by making the motor output adjustable through multiple operation modes (first through fourth modes) that allow the motor to operate at different power levels. The control unit dynamically switches between these modes based on operational requirements, enabling the system to use high power when needed for fastening speed while reducing power during continuous operation to prevent overheating and damage, thus resolving the contradiction between productivity and reliability
Solution Approach 2:
The patent changes the operational parameters of the motor by implementing multiple operation modes with different duty ratios and power outputs. The control unit adjusts these parameters dynamically, allowing the motor to operate at high output for short bursts to achieve fast fastening speed, then transitions to lower output modes to reduce temperature increase and mechanical stress during continuous operation, thereby maintaining both high productivity and reliability
2Productivity
If motor output is increased beyond necessary fastening torque requirements, then fastening speed is improved, but the risk of screw head damage increases
Solution Approach 1:
The system dynamically adjusts motor output through multiple operation modes, allowing high power delivery only when necessary for fastening speed while reducing power in subsequent operations. This dynamic control prevents excessive torque from being continuously applied to the screw head, thereby maintaining fastening speed while reducing the risk of damage
Solution Approach 2:
The patent implements periodic action by alternating between high-power operation modes for initial fastening and lower-power modes for subsequent operations. This periodic switching between high and low output states allows the system to achieve fast fastening speed initially while preventing continuous excessive torque that could damage the screw head
3Reliability
If motor output is limited to prevent temperature increase and mechanical stress, then reliability is improved, but fastening speed decreases
Solution Approach 1:
The control unit dynamically switches between multiple operation modes, allowing the motor to operate at high output when fastening speed is prioritized and at lower output when reliability and temperature control are prioritized. This dynamic adjustment resolves the contradiction by enabling both high-speed fastening and reliable continuous operation at different times during the fastening process
4Adaptability or versatility
If a motor with sufficiently high output is used to ensure high fastening torque capability, then the ability to handle various fastening targets is improved, but temperature increase during operation worsens
Solution Approach 1:
The patent implements multiple operation modes that allow the motor to deliver high torque when needed for various fastening targets while reducing power output during continuous operation. The control unit dynamically adjusts the duty ratio and operating mode based on the specific fastening requirements, enabling the motor to maintain high torque capability across different applications while managing temperature increase through periodic low-power operation
Solution Approach 2:
The system changes operational parameters by implementing multiple duty ratios and power levels corresponding to different operation modes. This allows the motor to operate at high power for short durations to achieve the necessary fastening torque for various targets, then transitions to lower power modes to reduce temperature increase, thereby maintaining versatility while controlling thermal effects
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for high-speed fastening while preventing motor and tool damage, improving durability and reducing temperature increases, enabling the use of higher-output motors while ensuring safe and efficient operation.
Implementation Method 1
The brushless DC motor employs a coil (winding) at a rotor-side and a permanent magnet at a stator-side and has a configuration where power driven by an inverter is sequentially energized to a predetermined coil to thus rotate the rotor
Implementation Method 2
a position detection element configured by a plurality of Hall ICs configured to detect a position of the rotor by detecting a magnetic force of the permanent magnet of the rotor
Data Source
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AI summary
The purpose of the present invention is to use a motor with as high an output as possible to complete tightening operations at a high speed while limiting continuous drive output. In a power tool having a plurality of impact operation modes, the motor thereof is controlled at a 100% duty cycle so as to rotate at a high speed in the period between pulling of a trigger and starting of an impact operation (71a-71b), and the duty cycle is changed to a low duty cycle matching the appropriate operation mode after an impact by an impact mechanism is started and a predetermined stroke is performed so that the motor is driven at the low duty cycle until the trigger is returned (arrow 71c-71d). The switching of the duty cycle is performed when the current flowing to the motor exceeds a threshold (I1).