Universal Motor Braking Device Reducing Brush Wear
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Solution Overview
Problem
Existing electrodynamic braking devices for universal motors face challenges in achieving efficient braking with reduced sparking and low brush wear, as they often result in excessive sparking and increased brush wear due to inadequate control over the transition from motor mode to braking mode.
Innovation Solution
An electrodynamic braking device that switches from motor mode to braking mode by feeding the field winding via a first and second switch, with the armature short-circuited via the second switch, and using control electronics to introduce a predetermined delay in actuating the second switch within each half cycle of the power grid voltage, optimizing the braking process by adapting to parameters like power grid voltage, rotational speed, and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If switching means are used to connect and disconnect field winding and rotor winding to power grid during braking mode, then braking function is achieved, but excessive sparking and increased brush wear occur
Solution Approach 1:
The patent applies preliminary action by briefly re-establishing motor mode operation before executing the braking mode. Control electronics temporarily activate both field winding and armature winding with proper phase gating, creating optimal commutation conditions that prevent sparking during the subsequent braking operation. This preparatory motor mode action within each half cycle ensures brushes are properly positioned and commutation is optimized before the harmful braking current is applied.
Solution Approach 2:
The patent implements periodic action by repeatedly applying brief motor mode pulses within each half cycle of the alternating current supply during braking operation. This periodic re-synchronization of the motor mode creates continuous optimal commutation conditions throughout the braking process, preventing cumulative sparking and brush wear while maintaining effective braking force.
2Productivity
If armature is short-circuited during braking mode, then braking efficiency is improved, but commutation quality deteriorates causing increased sparking
Solution Approach 1:
The control system performs preliminary action by temporarily deactivating the armature short-circuit and re-establishing motor mode operation before applying braking. This brief motor mode pulse re-synchronizes the commutation timing and positions the brushes optimally, ensuring high-quality commutation during the subsequent braking phase when the armature is short-circuited for efficient deceleration.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the timing and duration of motor mode pulses within each half cycle based on the motor's operational state. By precisely controlling the phase gating angles and pulse widths, the system optimizes commutation quality parameters while maintaining effective braking performance through controlled armature short-circuiting.
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 reduces sparking and brush wear by ensuring gentle high-speed braking with improved commutation under the brushes, achieving efficient braking while minimizing damage to the collector and extending brush service life, all while being cost-effective and adaptable to various operational conditions.
Implementation Method 1
a field winding of the universal motor is fed from a power grid via a first and a second switch
Implementation Method 2
an armature of the universal motor is short-circuited via the second switch
Data Source
AI summary
An electrodynamic braking device for a universal motor includes a field winding configured to be fed from a grid during a braking operation, and an armature that is configured to be directly short-circuited. A braking process is performed by means of control electronics. Good braking is achieved with relatively low brush wear. Such an electrodynamic braking device can be used effectively for a power tool.