Tham khảo tài liệu 'open-source robotics and proces control cookbook edwards l 242p newnes elsevier 2005 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 3 To understand what s going on here you need to think about the mechanics of the situation. Each position of the stepper s rotor is a stable mechanical state for a certain corresponding electrical magnetic state of the coils. This state can be visualized as a valley between two hills of a plot of net force vs. angle the motor tries to seek the low point in the valley where the clockwise and counterclockwise forces on the rotor are equal. If you put an external mechanical force on the rotor in say a clockwise direction you are pushing up one side of the hill. If you push all the way to the top then when you release the rotor it will fall down into the next valley . the next stable step position. When we advance the step phase in software we alter the electrical state of the coils which creates a new position of mechanical equilibrium. Effectively we move the two hills and valley along a quarter-phase which means the motor is no longer sitting in the middle of the valley. Since the clockwise and counterclockwise forces on the rotor are no longer equal the rotor turns until it is in an equilibrium position once again the step operation is then complete. However this process doesn t happen instantly because the rotor - and whatever mechanical load it s driving has inertia. The time required for the rotor to find its new equilibrium point depends among other things on the inertia which is determined by the mechanical load on the motor and the force exerted by the coils which is directly proportional to coil current. The above explains both why we observe unreasonable stepper noise at certain combinations of load and step rate and the fact that we can t necessarily go from stationary to maximum achievable step speed instantly. At slow speeds and or with light loads the motor will snap to each new equilibrium point very quickly compared to the step rate and will in fact stop at the bottom of the equilibrium valley waiting for the next change of magnetic state.
