Stepping Motor Driver Circuit Using Induced Voltage Detection
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Solution Overview
Problem
Stepping motors consume excessive power due to the need for high current to reliably rotate the rotor, which is particularly problematic for battery-driven portable equipment where power consumption needs to be minimized.
Innovation Solution
A driver circuit for stepping motors with two coils, where the motor drive current is controlled based on detected induced voltage during a high impedance period, and a short-circuit period is introduced to reduce noise and power consumption by optimizing the drive current and voltage waveforms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of current to the coils is set sufficiently large so that the rotor can rotate reliably, then the rotor rotation reliability is improved, but the power consumption increases
Solution Approach 1:
The patent applies dynamics by making the coil current amount variable rather than fixed. The current is dynamically adjusted based on the rotor's actual position and load conditions. The control device increases current when the rotor is near magnetic attraction positions (where more current is needed for reliable rotation) and decreases current when the rotor is between positions (where less current is sufficient), thus maintaining rotation reliability while reducing overall power consumption.
Solution Approach 2:
The patent changes the parameter of coil current amount based on rotor position. By detecting the rotor position and adjusting the current magnitude accordingly, the system optimizes the balance between reliable rotation (needing higher current at critical positions) and power consumption (using lower current at non-critical positions). This parameter adaptation resolves the contradiction between reliability and energy efficiency.
2Use of energy by moving object
If a high impedance period is provided to measure induced voltage for controlling motor drive power, then power consumption is reduced and power control is improved, but noise due to kickback is generated
Solution Approach 1:
The patent converts the harmful kickback noise into a useful signal. Instead of treating the induced voltage (which causes kickback noise) as a problem to be eliminated, the system utilizes this induced voltage as the measurement signal for detecting rotor position and controlling motor drive power. The high impedance period, which would normally generate noise, is repurposed as the measurement window where the induced voltage naturally occurs and can be detected for control purposes.
Solution Approach 2:
The patent introduces a measurement period as an intermediary phase between drive states. During this high impedance measurement period, the system briefly transitions to a high impedance state specifically for detecting induced voltage, then quickly returns to the drive state. This intermediary measurement period allows power control based on actual rotor conditions while limiting the duration of kickback noise generation.
3Use of energy by moving object
If conduction is disabled near inversion of the polarity of the drive voltage where contribution to rotational force is small, then power consumption is reduced, but the timing optimization becomes complex
Solution Approach 1:
The patent applies periodic action by dividing the drive cycle into distinct phases: drive periods where current flows to generate rotational force, and high impedance measurement periods where conduction is disabled. Within each drive cycle, the system periodically switches between these states, disabling conduction specifically during polarity inversion periods when the contribution to rotational force is minimal. This periodic on-off pattern reduces power consumption while maintaining effective rotation during the drive phases.
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 reduces power wastage, prevents loss of synchronization, and minimizes noise generation, allowing for efficient motor control with reduced power consumption and eliminating the need for additional position detectors like Hall devices, thereby enhancing energy efficiency and cost-effectiveness.
Implementation Method 1
an induced voltage generated at that coil is detected
Data Source
AI summary
A stepping motor includes two coils and has supply currents to the two coils with different phases so that a rotor is rotated by the two coils. During a period where one coil is in a high impedance state, an induced voltage generated at that coil is detected. An output control circuit controls the magnitude of motor drive current supplied to the two coils in accordance with the detected induced voltage state. Then, prior to entering the high impedance state from the drive state, a short-circuit period is provided for short circuiting both terminals of the coil.