Actuator Motor Speed Control via Voltage Chopping and Differential Braking
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Solution Overview
Problem
Existing actuators for movable elements in buildings, such as roller shutters and blinds, face challenges in varying speed due to constant torque and speed limitations, especially when the load is driven by gravity, leading to unsafe conditions like uncontrolled movement during torque variations.
Innovation Solution
An actuator with a single-phase asynchronous motor and a differential brake system, controlled by an electronic circuit that adjusts the supply voltage and torque control unit, allowing for speed variation over a wide range, including low speeds when the load is driven by gravity, using a triac for voltage chopping and a microcontroller for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If voltage chopping is used to reduce motor speed, then energy consumption is reduced, but the motor speed cannot be reduced sufficiently when the load is driven by gravity
Solution Approach 1:
The brake torque is dynamically adjusted based on motor speed and load conditions. At high speeds, the brake provides strong retarding torque for rapid deceleration. As speed decreases, the brake torque is reduced to allow the motor to maintain control. This dynamic adjustment enables sufficient speed reduction even when the load is driven by gravity, while maintaining energy efficiency.
Solution Approach 2:
The system changes the operating parameters of the motor by adjusting the supply voltage through chopping. The microcontroller dynamically modifies the voltage parameters based on detected speed and load conditions, enabling the motor to operate efficiently across a wide speed range while maintaining adequate braking torque when needed.
2Loss of energy
If the motor operates as an asynchronous generator when the load is driving, then energy recovery is possible, but speed control becomes unstable and catastrophic runaway can occur
Solution Approach 1:
The microcontroller continuously monitors motor current, speed, and operational state to detect when the motor is operating as an asynchronous generator. Based on this feedback, the system dynamically adjusts the brake torque to maintain stable speed control. The feedback mechanism prevents catastrophic runaway by detecting abnormal conditions and applying appropriate braking force to maintain reliable operation.
Solution Approach 2:
The brake system acts as an intermediary between the motor and the load, providing controlled retarding torque even when the motor operates as an asynchronous generator. This intermediary braking force stabilizes the system during energy recovery operations, preventing the instability and runaway conditions that would otherwise occur when the load drives the motor.
3Object-affected harmful factors
If a hysteresis brake is used to provide regular braking, then mechanical friction and clicking noise are eliminated, but motor power must be significantly increased
Solution Approach 1:
The system merges the electromagnetic braking action with the mechanical differential brake to achieve smooth, friction-based deceleration without the drawbacks of traditional hysteresis brakes. The controlled retarding torque is applied through the differential brake mechanism, providing regular braking without mechanical friction and clicking noise while avoiding the need for significantly increased motor power.
4Device complexity
If the motor speed is kept constant near synchronous speed, then simple motor control is maintained, but the ability to provide progressive start and smooth docking is limited
Solution Approach 1:
The system dynamically adjusts motor speed throughout the operation cycle. During startup, the motor accelerates progressively rather than starting at full speed. During docking, the motor speed is reduced to enable smooth positioning. The microcontroller continuously adjusts voltage and brake torque to optimize speed profiles, providing progressive start and smooth docking while maintaining relatively simple control circuitry.
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 safe and controlled movement of movable elements by varying speed according to load conditions, reducing torque and energy consumption, and preventing overloads, with the ability to maintain motor operation as a motor even when the load drives it, ensuring smooth operation and safety.
Implementation Method 1
using a triac for voltage chopping
Implementation Method 2
an alternating current induction electric motor
Implementation Method 3
a brake (BRK) of the differential type
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The actuator (ACT) has an electric induction motor (MOT) supplied at constant frequency for driving a mobile element (LD) in opposite directions. A locking brake (BRK) e.g. disc type brake, locks the movements of the element in the absence of movement of the motor, where the brake is of differential type. A cut off device including a triac reduces an effective value of supply voltage of the motor. The brake is arranged such that the motor always operates as motor. An independent claim is also included for a method for adjusting the speed of rotation of an electric induction motor of an actuator.