Cogging Torque Measurement via Sinusoidal Voltage and Inertia Calculation
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Solution Overview
Problem
Existing methods for measuring cogging torque in motors face challenges such as difficulty in accurately measuring small torque values and the need for a larger driving motor to achieve accurate measurements, which results in a bulky measurement apparatus, and the inability to solely measure cogging torque due to current-induced torque pulsations.
Innovation Solution
A cogging torque measuring apparatus that includes a drive mechanism for rotating the motor without energization, a rotation angle detector, an angular acceleration calculating unit, a torque calculating unit, and a signal processing unit to determine the cogging torque waveform, allowing for accurate measurement without the need for a high moment of inertia driving motor and preventing current-induced torque pulsations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a torque meter is used to measure cogging torque by connecting the motor to be measured to a driving motor, then torque detection is possible, but the moment of inertia of the driving motor must be much higher than that of the motor to be measured, resulting in a bulky apparatus
Solution Approach 1:
The patent extracts the torque detection function from a separate torque meter and driving motor system, and instead uses the motor to be measured itself as the rotating object. By applying voltage to the motor and detecting current values, the torque is calculated directly from the motor's own electrical parameters, eliminating the need for external torque measurement equipment with high moment of inertia.
Solution Approach 2:
The patent replaces the mechanical torque measurement system (torque meter and driving motor) with an electrical measurement system. Instead of mechanically measuring torque through a torque meter, the system calculates torque by detecting current values and using the motor's electrical parameters, substituting mechanical measurement with electrical sensing and calculation.
2Speed
If a motor is energized during measurement to rotate the rotor, then rotation is achieved, but current-induced torque pulsations prevent sole measurement of cogging torque
Solution Approach 1:
The patent applies periodic action by using sinusoidal voltage with a specific frequency that is not an integer multiple of the motor's electrical angle frequency. This periodic voltage application creates smooth rotational motion while avoiding resonance and current-induced torque pulsations that would occur at harmonic frequencies, thereby enabling pure cogging torque measurement.
Solution Approach 2:
The patent changes the voltage frequency parameter to a value that is not an integer multiple of the electrical angle frequency. By adjusting this parameter, the system avoids resonant conditions and current-induced torque pulsations, allowing the measurement to capture only the cogging torque component without contamination from electrical torque variations.
3Measurement precision
If the motor is not energized during measurement, then cogging torque can be measured purely, but the motor cannot be rotated to perform the measurement
Solution Approach 1:
The patent replaces the mechanical rotation system with an electrical control system. By applying low-frequency sinusoidal voltage to the motor, the system achieves smooth rotational motion without energizing the motor in a way that会产生 current-induced torque pulsations. This allows the motor to rotate while maintaining pure cogging torque measurement conditions.
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
Enables accurate measurement of cogging torque in a smaller apparatus, even for large motors, while preventing current-induced torque pulsations, allowing for precise measurement of cogging torque alone.
Implementation Method 1
an angular acceleration calculating unit for second order differentiating the angle of rotation to calculate an angular acceleration
Implementation Method 2
a torque calculating unit for multiplying the angular acceleration by a moment of inertia of a rotor in the motor to calculate a torque
Data Source
AI summary
A method for determining a cogging torque may include applying a substantially constant rotation torque to an output shaft of a motor without electrically energizing the motor; detecting, an angle of rotation of the output shaft of the motor at each of a plurality of angles of rotation; calculating an angular acceleration of the motor at each of the plurality of angles of rotation by second order differentiating the angle of rotation; calculating a measured torque value at each of the plurality of angles of rotation by multiplying the angular acceleration by a moment of inertia of a rotor in the motor; obtaining a measured torque waveform of the measured torque value at each of the plurality of angles of rotation as a function of the plurality of angles of rotation; and calculating a cogging torque waveform based on a frequency of the measured torque waveform.