Digital BLDC Motor Control for Scanning Apparatus
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Solution Overview
Problem
Conventional analogue Phase-Locked Loop (PLL) type BLDC motors used in image scanning apparatuses struggle to maintain constant speed across various speed bands, leading to overshoot or undershoot, noise, incorrect paper margins, and distorted image definition during paper transfer.
Innovation Solution
A digital control method for BLDC motors is implemented, using a digital gain value stored in a lookup table to generate a PWM signal based on sensed driving information and control commands, allowing for precise control of speed and direction to maintain constant speed across multiple speed bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an analogue PLL type BLDC motor is used, then the motor structure is simple and manufacturing is easier, but the speed cannot be maintained constant in various speed bands
Solution Approach 1:
The patent replaces the mechanical analogue PLL circuit with a digital control system using a microcontroller and digital signal processing. The digital controller implements a digital PLL algorithm that can dynamically adjust gain values through software, eliminating the need for physical RC component adjustments and enabling precise speed control across multiple speed bands while maintaining the simplicity of the motor structure.
Solution Approach 2:
The patent changes the control parameter from fixed analogue gain values determined by physical RC components to variable digital gain values that can be dynamically adjusted through software. This allows the system to adapt gain values for different speed bands, maintaining constant speed control across expansion/reduction operations while keeping the motor structure simple.
2Device complexity
If the gain value is fixed using resistance and capacitor, then the circuit design is simpler, but the constant speed can only be maintained in a certain speed band
Solution Approach 1:
The patent transforms the static fixed gain value system into a dynamic adaptive system. The digital controller continuously monitors motor speed and automatically adjusts the gain value based on the current speed band and operational requirements. This dynamic adjustment enables constant speed maintenance across multiple speed bands while keeping the circuit design relatively simple through software-based control.
Solution Approach 2:
The patent creates a universal control system that can handle multiple speed bands and various operational modes (expansion, reduction, constant speed) using a single digital controller. The digital gain value storage unit and adaptive control algorithm provide multi-functionality, replacing the need for multiple fixed gain circuits designed for different speed bands.
3Device complexity
If an analogue PLL type BLDC motor is used, then the driving circuit is simpler, but noise occurs during operations and paper transfer accuracy deteriorates
Solution Approach 1:
The patent replaces the analogue driving circuit with a digital driving circuit that generates PWM signals through digital signal processing. This digital approach eliminates the noise inherent in analogue circuits while maintaining relatively simple circuit design. The digital controller provides precise control that improves paper transfer accuracy and eliminates the overshoot/undershoot problems that cause noise and distortion.
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
The digital control method effectively maintains constant speed across various speed bands, reducing noise, ensuring accurate paper transfer, and preventing image distortion, thereby improving the operational performance of image scanning apparatuses.
Implementation Method 1
A BLDC motor is a brushless motor that performs rectification electronically
Implementation Method 2
it is necessary to sense location information of a rotator using a Hall sensor
Implementation Method 3
A digital control method for BLDC motors is implemented, using a digital gain value stored in a lookup table to generate a PWM signal
Data Source
AI summary
An image scanning apparatus includes a scanning unit which scans paper, a paper transfer unit which transfers the paper to the scanning unit using a BLDC (Brushless DC) motor, a sensor unit which senses driving information of the BLDC motor, a scan controlling unit which controls operations of the scanning unit, and generates a control command including information regarding a driving direction of the BLDC motor, a driving signal unit which generates a driving signal for controlling the BLDC motor, and a digital controlling unit which controls operations of the driving signal unit in a digital method based on a generated control command, sensed driving information and a digital gain value according to a driving direction of the BLDC motor.