Stepper Motor Drive Circuit for Back-EMF Detection in 2-Phase Excitation
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Solution Overview
Problem
Stepping motors using the 2-phase excitation method face challenges in detecting back electromotive force, which is essential for preventing step-out and achieving high-efficiency operation, as existing techniques require high-impedance states that are not applicable in 2-phase excitation methods.
Innovation Solution
A driving circuit that includes a constant current chopper circuit, detection window generation circuit, logic circuit, back electromotive force detection circuit, and current value setting circuit, allowing for precise detection of back electromotive force during zero-crossing of coil currents and minimizing disruptions to constant current chopper control, enabling feedback control in high-efficiency mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the 2-phase excitation method is used to drive the stepping motor, then the motor operates with balanced currents and improved efficiency, but the back electromotive force cannot be detected because the full-bridge circuit cannot be set to high-impedance state
Solution Approach 1:
The patent segments the control cycle into distinct phases: a constant current chopper control phase for normal motor operation, and a back electromotive force detection phase. During the detection phase, the full-bridge circuit is temporarily set to high-impedance state to enable back electromotive force measurement, while during the control phase, constant current control is applied to prevent step-out. This temporal segmentation allows both functions to coexist without interference.
Solution Approach 2:
The patent implements periodic switching between constant current chopper control and back electromotive force detection. The control circuit periodically sets the full-bridge circuit to high-impedance state at specific intervals to detect back electromotive force, then returns to constant current control. This periodic action ensures that motor operation is not disrupted while obtaining necessary feedback information for efficiency optimization.
2Reliability
If constant current chopper control is applied to prevent step-out, then the motor maintains reliable operation, but the back electromotive force detection becomes impossible due to circuit interference
Solution Approach 1:
The patent dynamically switches the operating mode of the full-bridge circuit between constant current control and high-impedance detection states. The control circuit monitors motor operation and temporarily transitions to high-impedance state when back electromotive force detection is required, then returns to constant current control when step-out prevention is needed. This dynamic switching allows the system to adapt between conflicting operational requirements.
Solution Approach 2:
The patent performs back electromotive force detection at predetermined timing intervals before step-out conditions develop. By periodically detecting back electromotive force in advance, the system can predict potential step-out conditions and adjust control parameters proactively, rather than reacting after step-out occurs. This preliminary detection action enhances overall system reliability.
3Measurement precision
If the full-bridge circuit is set to high-impedance state for back electromotive force detection, then measurement becomes possible, but constant current chopper control is disrupted
Solution Approach 1:
The patent changes the impedance parameter of the full-bridge circuit temporarily for back electromotive force detection. The control circuit switches the full-bridge circuit from low-impedance state (during constant current control) to high-impedance state (during back electromotive force detection), then returns to low-impedance state. This parameter change enables precise measurement while minimizing disruption to control continuity by limiting the high-impedance state to brief detection intervals.
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
Enables precise detection of back electromotive force and feedback control of current instruction values, reducing the risk of step-out and improving efficiency while maintaining high precision and responsiveness.
Implementation Method 1
a back electromotive force detection circuit to detect the back electromotive force of the coil when the detection window is in the open state
Data Source
AI summary
A driving circuit drives a stepping motor in synchronization with an input clock using a 2-phase excitation method. A constant current chopper circuit generates a pulse modulation signal such that the detection value of the coil current approaches a current setting value. A detection window generation circuit generates a detection window. The detection window becomes an open state at a timing at which the coil current IOUT becomes smaller than a predetermined threshold value. A logic circuit sets a full-bridge circuit to a high-impedance state when the detection window is in the open state and controls the full-bridge circuit according to the pulse modulation signal when the detection window is in the closed state. In the open state of the detection window, a back electromotive force (BEMF) detection circuit detects the BEMF of the coil. A current value setting circuit controls a current setting value based on the BEMF.