Torque Control via Current Segmentation in Electric Power Tools
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Solution Overview
Problem
Existing electric power tools face challenges in accurately setting tightening torque due to motor driving currents that include non-contributory excitation currents and neglecting inertial energy, making it difficult to achieve precise torque control without mechanical clutch mechanisms.
Innovation Solution
An electric power tool equipped with a permanent magnet synchronous motor and a controller that limits current contributing to torque generation to a predetermined maximum value, considering inertia effects, allowing for accurate torque control through motor control alone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If motor driving current is used to calculate tightening torque, then torque control can be achieved, but the torque setting becomes inaccurate because motor excitation current not contributing to rotational torque is included
Solution Approach 1:
The motor current is segmented into two distinct components: excitation current (id) that does not contribute to torque generation, and torque current (iq) that directly produces rotational torque. This segmentation allows the control system to exclusively use the torque-contributing current component for torque calculation, thereby eliminating the measurement inaccuracy caused by including non-contributory excitation current in the torque determination.
2Measurement precision
If motor driving current is used to calculate tightening torque, then torque control can be achieved, but the torque setting becomes inaccurate because inertial energy of rotating body is not considered
Solution Approach 1:
The control system performs preliminary action by calculating and compensating for the inertial torque component before determining the final tightening torque. The inertial energy effect, represented by the term J×dω/dt (where J is moment of inertia and dω/dt is angular acceleration), is computed in advance and subtracted from the total motor torque. This preliminary compensation ensures that the remaining torque accurately reflects only the tightening torque applied to the workpiece, thereby improving both measurement precision and control reliability.
3Measurement precision
If mechanical clutch mechanism is used to set torque, then torque control can be achieved, but the device complexity increases
Solution Approach 1:
The patent replaces the traditional mechanical clutch mechanism with an electronic control system that uses permanent magnet synchronous motor control to achieve torque setting. Instead of using mechanical friction plates or clutch mechanisms to limit and set torque, the system calculates the required torque based on the torque current component (iq) and dynamically adjusts the motor current to achieve the desired tightening torque. This substitution eliminates complex mechanical torque-limiting mechanisms while maintaining or improving torque control precision through electronic calculation and control.
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 enables more accurate tightening torque setting solely by motor control, potentially eliminating or simplifying the mechanical clutch mechanism by dynamically limiting current to a maximum value that accounts for inertia and load conditions.
Implementation Method 1
a permanent magnet synchronous motor, and a controller configured to control an operation of the permanent magnet synchronous motor
Data Source
AI summary
An electric power tool is provided with a permanent magnet synchronous motor, and a controller. The controller is configured to control an operation of the permanent magnet synchronous motor. The controller includes a limiter that limits a current contributing to torque generation by the permanent magnet synchronous motor to a predetermined maximum set value based on a predetermined tightening torque. The controller calculates the maximum set value of the current that contributes to the torque generation by changing one of a rotation speed and an angular speed of the permanent magnet synchronous motor.