Brushless Motor Speed Control for Pan-Tilt-Zoom Cameras
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Solution Overview
Problem
Surveillance cameras using brushless motors struggle to operate smoothly at both high and low speeds, leading to image blurring and misinterpretation due to limitations in existing commutation modes, particularly at low speeds where hall sensors provide insufficient resolution.
Innovation Solution
A brushless motor speed control system integrating sinusoidal synchronous commutation at low speeds and block commutation at high speeds, with seamless transitions between modes, using programmable controllers to drive multiple PWMs synchronously and employing trapezoidal Hall Effect feedback looping with PID error correction, eliminating the need for expensive digital encoders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If block commutation mode is used for high speed operation, then high speed tracking capability is improved, but low speed operation produces image blurring and stuttering
Solution Approach 1:
The system dynamically switches between block commutation mode for high speeds and sinusoidal synchronous commutation mode for low speeds. The controller monitors motor speed and automatically selects the appropriate commutation mode to maintain smooth operation and clear imaging across the entire speed range, eliminating the stuttering and blurring artifacts that occur with block commutation at low speeds.
Solution Approach 2:
The invention changes the commutation waveform parameter from block (trapezoidal) to sinusoidal based on operating speed. At low speeds, sinusoidal commutation provides continuous smooth torque delivery, preventing the positional discrimination problems and image artifacts associated with block commutation, while block commutation remains optimal for high speed operation.
2Speed
If hall sensors are used for commutation timing, then high speed block commutation is enabled, but low speed resolution is insufficient
Solution Approach 1:
The system uses an intermediary controller that processes hall sensor signals and determines the appropriate commutation mode based on detected speed. The controller acts as a mediator between the hall sensors and motor drive, selecting block commutation at high speeds and sinusoidal synchronous commutation at low speeds where hall sensor resolution becomes insufficient, thereby maintaining precise positional control across all operating conditions.
3Manufacturing precision
If digital encoders are used to improve low speed control, then smooth low speed operation is achieved, but system cost and complexity increase
Solution Approach 1:
The invention creates a virtual encoder effect by using the controller to generate sinusoidal commutation waveforms based on detected motor position and speed. This software-based approach replicates the smooth low-speed control characteristics of expensive digital encoder systems without requiring additional hardware components, thereby achieving cost-effective smooth low-speed operation.
Solution Approach 2:
The system replaces the mechanical/digital encoder hardware with a controller-based sinusoidal synchronous commutation system. By using software algorithms to generate precise commutation waveforms and control motor phases, the invention substitutes complex hardware encoding mechanisms with a more simple and cost-effective electronic control approach that achieves equivalent or superior low-speed performance.
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 smooth and precise control over a wide range of speeds, from very slow to high speeds, ensuring clear imaging without blurring, with fewer complex components and lower costs, capable of tracking objects moving quickly or slowly with high accuracy.
Implementation Method 1
the high speed mode employs trapezoidal Hall Effect feedback looping with programmable controller PID (Proportional, Integrated, Differential) error correction
Data Source
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AI summary
This system provides a wide range of smooth and precisely controlled low and high speeds for pan-tilt-zoom surveillance cameras, in which a brushless motor is controlled by a Microcontroller in a low speed mode by sinusoidal synchronous commutation, in a high speed mode by block commutation, and in in a transition phase from the low speed mode to the high speed mode by modulating integrated pulse-width modulation (PWM) square waves with sine waves. PID and lookup table registers are used by a microcontroller for a smooth transition from high speed mode to low speed mode, and from low speed mode to high speed mode, phase locking a sine position during transitions, in order to give a surveillance camera an ability to quickly move from one target to another at up to 100 degrees per second yet track objects that are moving very slowly.