Electric Motor Control for Stuck Screw Torque Management
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Solution Overview
Problem
Existing power tools with electronically commutated electric motors lack the ability to automatically adjust torque based on load conditions, leading to issues with stuck or stiff screws during screwdriving operations, and fail to prevent overtightening.
Innovation Solution
A method for controlling power tools with electronically commutated electric motors that starts with a reduced pulse duty factor, increasing it if the motor does not move within a specific time, and further adjusts based on motor rotation, using a combination of increased duty cycles and directional changes to manage torque effectively, avoiding overloading and ensuring precise screw tightening or loosening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the motor is started with high speed regardless of operating switch position, then the screw tightening speed is improved, but the screw connection may be overtightened causing damage
Solution Approach 1:
The control system performs preliminary action by initially operating the motor at reduced speed regardless of the operating switch position. This preliminary low-speed operation allows the system to detect motor blocking conditions and prevent overtightening before it occurs. Only after confirming the motor is not blocked does the system proceed to normal high-speed operation based on the operating switch position.
2Ease of operation
If the motor operates with constant torque, then the screw tightening process is simple, but the motor cannot handle stuck or stiff screws
Solution Approach 1:
The control system implements feedback by continuously monitoring motor current and rotation status. When the motor current exceeds a threshold or rotation is detected as blocked, the system automatically increases torque by adjusting the pulse width modulation duty cycle. This feedback mechanism allows the system to maintain simple constant torque operation during normal conditions while automatically providing enhanced torque when stuck or stiff screws are detected.
3Force
If the pulse duty factor is increased to provide higher torque, then the motor can handle stuck screws, but the screw may be overtightened if applied continuously
Solution Approach 1:
The control system applies periodic action by using pulse width modulation to deliver torque in controlled pulses rather than continuously. The pulse duty factor is increased temporarily only when blocking is detected, and the system monitors rotation during each pulse. This periodic torque application allows the motor to overcome stuck screws while automatically preventing overtightening by stopping the pulse when the screw reaches proper tightness.
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 automatic adaptation of torque to handle stuck screws and prevents overtightening by gradually increasing torque as needed, ensuring efficient and precise screw operations without user confusion.
Implementation Method 1
the electric motor is controlled using a pulse width modulated signal whose duty cycle can be varied for speed control
Data Source
AI summary
An electric tool and a method for controlling an electric tool with an electronically commutated electric motor are described, comprising the following steps: (a) generating a pulse-width modulated signal whose duty cycle is variable for speed control; (b) starting the electric motor for a first pulse duration (48) with a reduced duty cycle of less than 100%, preferably with a minimum duty cycle; (c) increasing the duty cycle for a subsequent pulse duration if the electric motor (20) has not moved for a certain period of time (50) (Fig. 4).