Step Motor Driving Circuit with Counter Electromotive Force Step-Out Prediction
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Solution Overview
Problem
Step motors often experience synchronization loss due to overload or abrupt speed changes, leading to step-out, which is typically addressed by increasing output torque and using additional components for position detection, resulting in increased cost and power loss.
Innovation Solution
A motor driving circuit that includes a counter electromotive force detecting unit and a step-out predicting unit to detect signs of step-out, allowing for increased torque before synchronization loss occurs, and a current limit circuit to prevent step-out by adjusting current and pulse modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor driving circuit is designed to obtain an excessive output torque having a margin based on an anticipated maximum load, then the step-out prevention capability is improved, but loss of power is increased
Solution Approach 1:
The invention detects signs of step-out in advance by monitoring counter electromotive force during the high impedance period, before actual step-out occurs. This allows the system to take preliminary corrective action (increasing current) to prevent step-out, rather than continuously operating with excessive torque margin. The detection timing is specifically set at a predetermined time after transition to high impedance period, enabling early warning of synchronization issues.
Solution Approach 2:
The invention dynamically changes the current parameter based on detected step-out signs. When counter electromotive force falls below a threshold, the system increases current flowing to the coil to prevent step-out. This dynamic parameter adjustment replaces the static approach of continuously providing excessive torque margin, reducing power loss while maintaining reliability.
2Measurement precision
If a sensor or vector control using a large scale digital calculation circuit is used to detect the position of the rotor, then the position detection precision is improved, but cost and logical area are increased
Solution Approach 1:
The invention extracts the essential information needed for step-out detection from the counter electromotive force signal during the high impedance period, rather than implementing full position detection systems. By monitoring only the counter electromotive force threshold during specific timing windows, the system obtains sufficient information to detect step-out signs without requiring complex sensors or large-scale digital calculation circuits for complete position tracking.
Solution Approach 2:
The invention uses a simple, low-cost detection method based on counter electromotive force monitoring during the high impedance period. This approach replaces expensive sensors and complex vector control circuits with a straightforward threshold comparison method that provides adequate step-out detection capability without requiring continuous high-precision position information.
3Speed
If the detection time is set immediately after transition to high impedance period, then the response speed is improved, but measurement precision is worsened due to transient effects
Solution Approach 1:
The system performs preliminary detection at a predetermined time after transition to high impedance period, allowing transient effects to subside before measurement. This timing strategy balances response speed with measurement accuracy by detecting step-out signs early in the high impedance period while avoiding the immediate transient phase that would corrupt the counter electromotive force signal.
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
The solution effectively prevents step-out by increasing torque and reducing the need for excessive margin, thereby reducing power consumption and component costs while maintaining precise control.
Implementation Method 1
a counter electromotive force detecting unit configured to detect a counter electromotive force generated between both ends of the coil
Data Source
AI summary
A motor driving circuit for driving a step motor includes a logical circuit synchronized with a step pulse signal to control a bridge circuit connected to a coil of the step motor and control electric power supplied to the coil of the step motor, a counter electromotive force detecting unit configured to detect a counter electromotive force generated between both ends of the coil, and a step-out predicting unit configured to assert a detection signal indicating a sign of step-out of the step motor, when the counter electromotive force detected at a detection time after the lapse of a time calculated by multiplying a predetermined coefficient to a length of a high impedance period of the coil since transition to the high impedance period is lower than a predetermined threshold voltage.