Stepping Motor Current Control via PWM Attenuation Modes
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Solution Overview
Problem
High-frequency noise generated during micro-step driving of stepping motors poses a challenge, as increasing PWM frequency requires expensive microcomputers and dedicated drivers, leading to increased costs and load.
Innovation Solution
A motor current control device with an H bridge circuit and control means that switches between charge, fast attenuation, and slow attenuation modes based on a predetermined PWM cycle, adjusting operation modes to match the positional relationship between the rotor and stator, thereby controlling motor current effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the PWM frequency is increased to suppress high-frequency noise, then the noise suppression effect is improved, but the cost increases due to requiring expensive microcomputers and dedicated drivers
Solution Approach 1:
The patent changes the PWM cycle parameter to be equal to or longer than one micro-step period, which fundamentally alters the relationship between PWM switching and motor current cycles. This parameter change allows noise suppression without requiring higher PWM frequencies or more expensive hardware components
2Object-affected harmful factors
If the PWM cycle is shortened to increase PWM frequency for noise suppression, then the noise suppression effect is improved, but the load on the microcomputer increases and cost increases
Solution Approach 1:
By setting the PWM cycle to be equal to or longer than one micro-step period, the patent transforms the control approach from high-frequency switching to lower-frequency switching with longer cycles. This reduces the processing load on the microcomputer while still achieving noise suppression through the extended current control period
3Object-affected harmful factors
If a dedicated motor driver or expensive microcomputer is used to shorten PWM cycle, then the noise suppression effect is improved, but the cost increases
Solution Approach 1:
The patent makes the existing microcomputer and motor driver perform the noise suppression function through software control of the PWM cycle, rather than requiring dedicated hardware. The control unit uses the existing resources to achieve noise suppression by extending the PWM cycle to match or exceed the micro-step period
Solution Approach 2:
The key parameter change is setting PWM cycle ≥ micro-step period, which allows the use of standard, inexpensive microcomputers and drivers instead of dedicated expensive components. This parameter relationship enables noise suppression using conventional hardware resources
Data Source
AI summary
In order to suppress high-frequency noise in micro-step driving of a stepping motor, a motor control device (100) includes an H bridge circuit (20) and control means for driving a switching element of the H bridge circuit (20) with a PWM signal and for setting a charge mode, a fast attenuation mode, or a slow attenuation mode for a motor coil. In a range from an electrical angle where the reference current value starts descending to an electrical angle of +52°, the control means switches the H bridge circuit (20) every PWM cycle to the charge mode and then to the slow attenuation mode. In a range exceeding +52° and to +90 degrees where the reference current value starts ascending, the control means switches the H bridge circuit (20) every PWM cycle to the charge mode and, if the motor current exceeds the reference current value, then the control means switches it to the fast attenuation mode and further to the slow attenuation mode.