Universal Motor Speed Control System with Closed-Loop Feedback
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Solution Overview
Problem
Conventional universal motors experience noise, speed fluctuations, reduced torque at low speeds, high starting currents, and vibrations due to their inability to maintain constant speed and efficient control, especially when used with reduction gearboxes at high speeds.
Innovation Solution
A speed control system for universal motors that includes a speed detecting unit and a controller with slow start, speed control, and stopping-protecting units, utilizing a start flag, acceleration weight, rotating speed command input, computing, and compensation modules to smoothly increase speed, correct speed differences, and protect against low speed or stoppage, thereby stabilizing speed and maintaining cutting ability across speed ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the universal motor is operated at high speed to reduce volume, then the motor volume is reduced, but noise increases and speed stability deteriorates
Solution Approach 1:
The patent implements a closed-loop speed control system using a speed detecting unit (Hall element) that continuously monitors the motor speed and feeds back to the controller. The controller compares the detected speed with the target speed and adjusts the conduction angle of the AC voltage accordingly, maintaining stable speed operation even at high speeds, thereby reducing noise and speed fluctuations while keeping the motor compact.
Solution Approach 2:
The patent employs dynamic speed control by adjusting the conduction angle of the AC voltage based on real-time speed feedback. The system can adaptively change operating parameters during runtime, allowing the motor to maintain optimal performance across different speed ranges, reducing noise and vibration while preserving compact dimensions.
2Speed
If the conduction angle of AC voltage is restricted to control speed, then speed adjustment is achieved, but torque is reduced at low speeds
Solution Approach 1:
The closed-loop control system continuously monitors speed and adjusts the conduction angle dynamically. When low speed is required, the system precisely controls the conduction angle to maintain adequate torque while achieving speed reduction. The feedback mechanism ensures that torque is optimized for the current operating condition, preventing excessive torque loss at low speeds.
Solution Approach 2:
The patent changes the conduction angle parameter dynamically based on speed requirements. By optimizing the conduction angle for different operating conditions rather than using fixed restriction, the system maintains better torque characteristics at low speeds while still achieving effective speed control.
3Productivity
If the universal motor starts directly, then starting is immediate, but starting current increases and vibration occurs
Solution Approach 1:
The patent implements a slow-start function that gradually increases the conduction angle from a small initial value to the target value during motor startup. This preliminary gradual excitation prevents sudden inrush current and reduces mechanical vibration and shock to the load, while still achieving quick startup overall. The acceleration weight parameter controls the rate of conduction angle increase.
4Device complexity
If simple speed adjustment device is used, then device complexity is low, but constant speed control is impossible
Solution Approach 1:
The patent employs a feedback-based speed control system using a Hall element to detect rotor position and speed, with the controller adjusting the conduction angle accordingly. This relatively simple feedback mechanism achieves precise constant speed control, maintaining speed stability within acceptable tolerances without requiring complex control hardware.
Data Source
AI summary
A speed control system of a universal motor is electrically connected with a universal motor and includes a speed detecting unit and a controller. The controller is provided with a slow start unit, a speed control unit and a stopping-protecting unit. The slow start unit enables the rotating speed of the universal motor to increase smoothly, and the speed control unit controls and compensates the rotating speed of the universal motor in a way of closed loop, able to achieve effect of stepless speed adjustment and, when used at low speed, having cutting ability similar to that when operated at high speed. The stopping-protecting unit is able to automatically cut off power and carry out protection when machine table is stopped.