DC Motor Ripple Count Detection for Start-Up and Braking Positioning
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Solution Overview
Problem
Existing sensor-less solutions for determining the armature position of brushed DC motors are ineffective during the start-up and braking phases of operation, as they fail to detect the ripple component in the armature current during these transitional phases.
Innovation Solution
A method and system that determine the missed ripple count during transitional phases by using the determined ripple period or frequency from the steady-state phase, applied to a transitional time interval, allowing for reliable positional determination without external sensors, through digital logic processing and look-up tables or formulas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensor-less ripple count detection is used during steady state operation, then the armature position can be determined effectively, but the ripple component remains undetected during start-up and braking phases
Solution Approach 1:
The system performs preliminary actions by detecting and storing ripple characteristics (frequency, amplitude, waveform shape) during the steady-state phase before transitional phases occur. This stored information is then used to compensate for missed ripple counts during start-up and braking, ensuring continuous position accuracy across all operating phases.
Solution Approach 2:
The invention creates a digital copy or model of the ripple characteristics during steady-state operation. This ripple model is then applied during transitional phases where direct ripple detection fails, allowing the system to estimate position based on the stored ripple pattern rather than requiring actual ripple detection during those phases.
2Reliability
If external positional sensors like Hall effect sensors are used, then position can be determined during all phases including start-up and braking, but the device complexity and cost increase
Solution Approach 1:
The system uses its own existing current sensing circuitry to detect ripple characteristics during steady-state operation, eliminating the need for external positional sensors. The motor's own electrical characteristics serve as the sensing mechanism, reducing component count and system complexity while maintaining full-phase position detection capability.
Solution Approach 2:
The current sensing circuit performs multiple functions: it detects both the drive current for motor control and the ripple component for position detection. This multi-functionality eliminates the need for separate Hall effect sensors or other external positional sensing devices, reducing overall system complexity.
3Loss of information
If ripple detection is attempted during start-up and braking phases, then position information can be obtained, but the ripple component is too weak or distorted to be reliably detected
Solution Approach 1:
The system uses feedback from steady-state ripple detection to inform transitional phase operation. By continuously monitoring ripple characteristics during steady-state and using this information to calculate position during transitions, the system maintains accurate position tracking even when direct ripple detection during transitions would be unreliable.
Solution Approach 2:
The system prepares position determination data during steady-state operation before transitional phases begin. By pre-calculating ripple characteristics and storing them for later use, the system ensures position information is available during transitions without requiring high-precision detection during those difficult phases.
Data Source
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AI summary
A method and a system for ripple count detection of a DC motor are provided. The method and the system determine a missed ripple count for transitional phases of operation, including the start-up and/or braking phases, based on a determined ripple period or frequency in the steady-state phase of operation. By applying this determined ripple period or frequency to a transitional time interval, the number of missed ripples for each transitional phase of operation can be reliably determined in digital logic, without the aid of external positional sensors.