Asymmetrical Magnetization Ripple Counter for Motor Position Detection
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Solution Overview
Problem
Existing electric motors experience increased vibration and noise when trying to detect rotating speed and position using current signals, particularly when the number of coils is an integral multiple of the number of brushes, making it difficult to generate a clear current ripple signal.
Innovation Solution
An electric motor with an asymmetrical magnetization or magnetic field distribution, combined with brushes arranged symmetrically around the rotation axis, allows for the use of an asynchronous counter method to detect the rotating speed and position without increasing vibration or noise, using an asymmetrical arrangement of magnet elements and brush widths to produce distinct current ripple peaks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the number of coils is an integral multiple of the number of brushes, then the motor structure is simplified and easier to manufacture, but the current ripple signal becomes difficult to detect and vibration increases
Solution Approach 1:
The patent applies asymmetry by making the number of coils not an integral multiple of the number of brushes (specifically, the number of coils is not divisible by the number of brushes). This asymmetric configuration creates distinct current ripple peaks during commutation, enabling clear detection of rotor position and speed while reducing vibration and noise. The asymmetric design breaks the symmetry that would otherwise cause overlapping commutation events and indistinguishable current signals.
2Stability of the object's composition
If brushes are arranged symmetrically around the rotation axis, then the motor operates more smoothly with balanced forces, but the current ripple signal becomes less distinct for position detection
Solution Approach 1:
The patent resolves this contradiction by combining symmetric brush arrangement with asymmetric coil distribution. The brushes remain symmetrically positioned for stable operation, but the number of coils is specifically chosen to not be an integral multiple of the brush count. This creates an asymmetric electrical configuration that generates distinct current ripple peaks, enabling accurate position detection while maintaining the mechanical stability provided by symmetric brush placement.
3Device complexity
If the number of segments changes simultaneously in both brushes, then the commutation process is simplified, but the generated current signal contains overlapping information that is difficult to detect
Solution Approach 1:
The patent addresses this by configuring the number of coils such that commutation events in different brushes do not occur simultaneously in a symmetric pattern. The asymmetric coil-to-brush ratio ensures that at least one brush experiences a distinct commutation event at any given time, creating separable current ripple peaks that are easy to detect and process for determining rotor position and speed.
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 solution enables precise detection of the rotating speed and position of the motor with reduced noise and vibration, using an asymmetrical magnetic field and brush arrangement to generate a clear, easily detectable current ripple signal, even at low rotation speeds.
Implementation Method 1
The stator has an asymmetrical magnetization or an asymmetrical magnetic field
Implementation Method 2
the magnetic fields are distributed asymmetrically or irregularly around the rotation axis
Implementation Method 3
the excitation circuit of the electric motor as a 'ripple counter' or as an asynchronous counter
Implementation Method 4
By detecting the current of the motor, the number of segments in contact with brushes can be speculated, and the rotating speed and position of the rotor is possible to be calculated
Data Source
Figure 1~2
Figure 3a~3f
Figure 4a~4d
AI summary
An electric motor includes at least one first brush and at least one second brush, which are arranged in a stationary fashion and arranged to contact a commutator that rotates with a rotor. The commutator includes at least one cylindrical section with a circumferential surface on which a plurality of segments are arranged with insulating sections interposed between them. In order to detect the rotating speed and position of the rotor, the motor includes brushes with asymmetric circumferential widths or angles or a stator with an uneven magnetization. The motor is arranged to detect only one signal when the rotor rotates for an angle between two adjacent segments.