Diffusion Wheel PWM Startup Control for Low-Noise Laser Projection
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Solution Overview
Problem
Laser projection systems face challenges in achieving efficient startup and shutdown processes due to high noise levels and inefficiencies caused by rapid changes in drive current during motor rotation, which affect the display quality and reliability.
Innovation Solution
The implementation of a control method that uses a combination of pulse width modulation signals with varying duty cycles to softly start and stop the diffusion wheel motor, ensuring a gradual transition from initial to target drive current, thereby reducing noise and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If rapid changes in drive current are used during motor startup and shutdown, then startup and shutdown speed are improved, but noise levels increase and system reliability deteriorates
Solution Approach 1:
The patent applies periodic action by using pulse width modulation (PWM) signals with varying duty cycles to control the motor drive current. During startup, the duty cycle increases progressively from 0% to 100% in stages, and during shutdown, it decreases from 100% to 0% in stages. This periodic modulation replaces direct rapid switching, reducing electrical noise and current spikes while maintaining efficient startup and shutdown performance.
2Loss of time
If rapid changes in drive current are used during motor startup and shutdown, then startup and shutdown time are reduced, but system reliability worsens
Solution Approach 1:
The patent applies preliminary action by preparing the motor for startup through gradual duty cycle increases before full operation begins. The multi-stage PWM approach pre-conditiones the motor and driver circuitry, preventing sudden current shocks that would reduce reliability. Similarly, during shutdown, the gradual duty cycle reduction pre-prepares the system for stopping, avoiding abrupt current cutoffs that could cause electrical stress or instability.
3Speed
If high drive current duration is extended, then motor acceleration is improved, but noise levels and energy loss increase
Solution Approach 1:
The patent applies dynamics by continuously adjusting the drive current through varying PWM duty cycles rather than maintaining a fixed high current. During startup, the duty cycle dynamically increases from 0% to 100% in controlled stages, providing just enough current at each moment for efficient acceleration. During operation, the duty cycle can be dynamically reduced to maintain speed with lower energy consumption. This dynamic control optimizes the balance between acceleration performance and energy efficiency.
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 results in high startup and shutdown efficiency with reduced noise levels, enhancing the overall performance and reliability of the laser projection system by minimizing the duration of high drive currents and stabilizing the motor rotation speed.
Implementation Method 1
a temperature sensor configured to detect an ambient temperature
Implementation Method 2
determine a duty cycle of a second startup pulse width modulation signal according to the target starting current, and provide the second startup pulse width modulation signal to the diffusion wheel driving circuit
Implementation Method 3
The diffusion wheel driving circuit is configured to drive the three-phase motor
Data Source
AI summary
A laser projection apparatus includes a main control circuit, a diffusion wheel driving circuit and a temperature sensor. The temperature sensor is electrically connected to the main control circuit, and configured to detect an ambient temperature. The main control circuit is configured to: determine a target starting current according to the ambient temperature; determine a duty cycle of a second startup pulse width modulation signal according to the target starting current, and provide the second startup pulse width modulation signal to the diffusion wheel driving circuit; and output an operating pulse width modulation signal to the diffusion wheel driving circuit when the diffusion wheel reaches a target rotation speed. The target starting current is a minimum drive current required to drive the motor from standstill to starting to rotate. The target rotation speed is a preset speed at which the diffusion wheel operates normally and speckles are eliminated.