Electric Sander BLDC Control for Low Harmonic Interference
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Solution Overview
Problem
Existing electric sanding machines are bulky, difficult to grip, and generate high harmonic interference, necessitating complex and expensive solutions for network compliance.
Innovation Solution
A compact, ergonomic design using a brushless direct current (BLDC) motor with a slotless rotor-stator configuration, integrated cooling, and sensorless control, along with optimized power correction to minimize harmonic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a conventional motor design with shaft and bearings is used, then the motor can be assembled in conventional way, but the sanding machine becomes large and difficult to grip with one hand
Solution Approach 1:
The patent merges the motor shaft function with the tool shaft by directly fastening the rotor to the tool shaft, eliminating the need for a separate motor shaft. This integration reduces the overall motor size and volume while maintaining functional requirements, enabling compact sanding machine design that can be gripped with one hand.
Solution Approach 2:
The tool shaft is positioned to extend within the rotor of the drive motor, creating a nested configuration where the tool shaft is housed inside the rotor structure. This nesting arrangement optimizes space utilization and reduces the external dimensions of the motor assembly.
2Reliability
If the motor diameter is made large to accommodate conventional design, then assembly is simplified, but hermetic sealing with external cooling becomes difficult and dust particles can contaminate the cooling air
Solution Approach 1:
By integrating the tool shaft within the rotor and eliminating the separate motor shaft, the patent creates a more compact motor structure with reduced diameter. This enables effective hermetic sealing while maintaining external cooling pathways that are less susceptible to dust contamination.
3Use of energy by moving object
If a simple rectified control unit with large capacitor is used, then continuous current can be supplied, but very high harmonic components are generated that interfere with the electric network
Solution Approach 1:
The patent changes the operating parameters of the motor control by using sensorless control with optimized switching frequencies and pulse width modulation. This approach enables continuous current supply to the motor while significantly reducing harmonic components generated back to the electric network, complying with EN61000-3-2 standards.
4Object-generated harmful factors
If passive filtering with inductances and capacitors is used to reduce harmonics, then network interference is reduced, but the machine requires more space and has greater volume and weight
Solution Approach 1:
The patent replaces passive electrical filtering components (inductances and capacitors) with an active control system using sensorless vector control and optimized switching strategies. This substitution eliminates the need for bulky passive filtering components while achieving effective harmonic reduction, maintaining compact machine dimensions.
5Object-generated harmful factors
If active power correction with step-up topology is used, then harmonic components are reduced, but the current goes through extra inductance and is switched one more time
Solution Approach 1:
The patent changes the control strategy by using sensorless vector control with optimized switching frequencies and pulse width modulation directly at the motor inverter stage. This approach achieves effective harmonic reduction without requiring additional active power correction stages, extra inductances, or additional switching operations, thereby reducing control unit complexity.
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
The design achieves a lightweight, ergonomic, and efficient sanding machine with reduced harmonic interference, eliminating the need for separate dust extraction systems and enabling comfortable one-handed operation.
Implementation Method 1
an electric drive motor that is brushless and without a shaft of its own, mounted in such a way that the rotor is fastened to the tool shaft and the stator is positioned in the outer housing
Implementation Method 2
Due to the strong magnetic field of the new NdFeB magnets, the motor has high power per volume and high efficiency
Data Source
Figure 1~2
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AI summary
A control method for an electric sanding machine, which method comprises rectification of the mains voltage and switched motor control. An external inductance L1 and an extra switch according to step-up topology have been incorporated to carry out power correction also during the time when the voltage is lower than the nominal voltage of the motor. This is preferable because the current and the voltage are lower than in a case where the power correction should be carried out during the whole cycle. Above all, the value at the external inductance L1 may be lower because the voltage is lower when the switching is carried out.