DC Motor Ripple Count Circuit for Sensorless Speed and Position
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Solution Overview
Problem
Conventional DC motor position systems using Hall Effect Sensors and magnetic rings are expensive and complex, requiring additional computations to determine rotor speed, leading to longer processing times.
Innovation Solution
A motor control system with a ripple count circuit that extracts the AC signal from the armature current to generate a pulsed output indicative of the rotor speed and position, eliminating the need for expensive controllers and magnetic rings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall Effect Sensors and magnetic rings are used to determine rotor speed, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the speed measurement information directly from the existing drive current signal by filtering out the ripple component, eliminating the need for separate Hall Effect Sensors and magnetic rings. The ripple frequency in the drive current is directly proportional to rotor speed, allowing speed determination without additional measurement components.
Solution Approach 2:
The drive current serves multiple functions: it drives the motor and simultaneously carries speed information through its ripple component. By utilizing the existing drive current for both motor operation and speed measurement, the system eliminates dedicated sensor components while maintaining measurement capability.
2Measurement precision
If Hall Effect Sensors and magnetic rings are used to determine rotor speed, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent removes expensive Hall Effect Sensors and magnetic rings from the system, replacing them with a signal processing approach that uses the existing drive current. This extraction of measurement capability from dedicated components to the control system significantly reduces manufacturing costs.
Solution Approach 2:
The patent replaces expensive physical sensors with a software-based signal processing solution implemented in the controller. This digital approach using existing current measurements is much cheaper than hardware sensors while providing equivalent or superior measurement precision.
3Measurement precision
If conventional computation methods are used to determine rotor speed from sensor signals, then measurement precision is improved, but processing time increases
Solution Approach 1:
The patent extracts speed information directly from the drive current ripple frequency without requiring separate sensor signal processing. This direct extraction method eliminates the time-consuming steps of reading external sensors, conditioning signals, and computing speed from magnetic flux variations.
Solution Approach 2:
The drive current continuously carries speed information throughout motor operation. By continuously monitoring the ripple frequency in the existing drive current, the system maintains continuous speed measurement without the discrete sampling and computation delays inherent in sensor-based systems.
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 solution provides a cost-effective and efficient method to determine the rotational speed and position of a DC motor, reducing processing time and system complexity.
Implementation Method 1
The amplifier is configured to amplify a drive current that drives rotation of a rotor included in a direct current (DC) motor
Implementation Method 2
The current differential circuit is configured to generate a derivative current signal that indicates an instantaneous rate of current change (d(i)/dt) of the drive current
Implementation Method 3
The bandwidth filter is configured to filter the derivative current signal based on a rotational speed (ω) of the rotor so as to output a first filtered signal
Implementation Method 4
The downstream low pass filter is configured to filter the first filtered signal based on the rotational speed (ω) of the rotor so as to output a second filtered signal that eliminates harmonics from the first filtered signal
Implementation Method 5
The comparator circuit is configured to compare the second filtered drive current to a reference voltage potential, and generate a pulsed output signal having a first output voltage level when a voltage level of the filter drive current is greater than or equal to the reference voltage potential
Implementation Method 6
The rotation of the rotor generates a mechanical force that drives a component
Data Source
AI summary
A motor control system includes a variable voltage supply in signal communication with a direct current (DC) motor. The DC motor includes a rotor induced to rotate in response to a drive current generated by a variable supply voltage delivered by the voltage supply. The rotation of the rotor generates a mechanical force that drives a component. A ripple count circuit is configured to filter the drive current based on a rotational speed (ω) of the rotor, and to generate a pulsed output signal indicative of the rotational speed (ω) of the rotor and a rotational position (θ) of the rotor.