Stepper Motor Sensorless Load Angle Detection via Back-EMF
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Solution Overview
Problem
Stepper motors typically operate with excessive current consumption due to a torque reserve, resulting in significant power losses, as they are controlled independently of the actual motor load, leading to inefficient energy use, especially in cost-sensitive applications where rotary sensors are not feasible.
Innovation Solution
A sensor-free method and circuit arrangement that detects the load angle of a stepper motor using counter-electromotive force (CEMF) to adjust chopper cycles, allowing for precise control of motor current based on the actual mechanical load, thereby reducing current consumption and power losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stepper motors are controlled with constant high current to ensure sufficient torque for maximum expected load, then torque reliability is improved, but energy consumption increases significantly
Solution Approach 1:
The patent applies dynamics by transitioning from static constant current control to dynamic current control that adapts to actual load conditions. The system continuously monitors load angle and adjusts motor current in real-time, ensuring sufficient torque for actual load while reducing current when load is light, thus resolving the contradiction between torque reliability and energy consumption
Solution Approach 2:
The patent implements feedback control by monitoring the load angle (derived from counter-EMF measurements) and using this information to regulate motor current. The feedback loop ensures that current is adjusted based on actual torque requirements, maintaining reliability while minimizing energy consumption during light-load operation
2Use of energy by moving object
If rotary sensors are installed to detect rotor position for precise current control, then energy efficiency is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies self-service by using the motor's own back-EMF signals to derive load angle information without external sensors. The counter-EMF generated during motor operation is processed to determine rotor position and load conditions, enabling sensorless control that improves energy efficiency while avoiding the complexity and cost of rotary sensors
Solution Approach 2:
The patent replaces the mechanical rotary sensor system with an electrical measurement approach. Instead of using physical sensors to detect rotor position, the system uses electrical measurements of counter-EMF to infer position and load angle, substituting a complex mechanical sensing system with a simpler electrical measurement and processing approach
3Force
If high motor current is used to maintain torque reserve for maximum load, then torque availability is improved, but power loss increases by factor of four or more
Solution Approach 1:
The patent applies partial action by providing torque only as needed for actual load conditions rather than maintaining excessive torque reserve. The system delivers full torque capability when maximum load is present but reduces current proportionally when load is lighter, eliminating the excessive action of maintaining constant high current and thereby reducing power loss while maintaining sufficient torque availability
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 enables stepper motors to operate with minimal current consumption, reducing power losses by up to 300% and maintaining sufficient torque, without the need for additional mechanical components or changes to the motor design.
Implementation Method 1
A sensor-free method and circuit arrangement that detects the load angle of a stepper motor using counter-electromotive force (CEMF) to adjust chopper cycles
Implementation Method 2
The torque and the holding torque of a stepper motor for the most part are proportional to the RMS (root mean square) value of the motor current, multiplied by the sine of the load angle
Data Source
AI summary
A method and a circuit arrangement are provided in which a mechanical load applied to the motor shaft or a load angle of the motor can be detected without sensors in a stepper motor. This is achieved substantially based on the fact that the load or the load angle creates a mutually induced voltage (back EMF) in the motor coils and the load or the load angle is detected by determining the phase shift of the motor voltage at at least one of the motor coil relative to the coil current at said motor coil connection, the phase shift being caused by the mutually induced voltage. A method and a circuit arrangement are also provided wherein the motor current of a stepper motor can be controlled according to load angle in such a way that the current consumption of the motor is relatively low.