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hi..
the stepping motor has some step for do 1 rotation, every kind of stepping motor sometimes different each other. during design, we able to calculate how many step for 1 rotation. then using this calculation we able to predict the movement..
suppose that the 1 rotation is 400 step, so when we want to make 45 deg movement, then we need 45/360*400..
then inside our firmware, we must record the last position, the last position value will have effect to the calculation result. so we able to use the stepping motor well and we don't need any feedback (sensor) for this.
Most instruments utilizing stepper motors have a reference or zero position sensor and are counting steps from this known position. On power on, they usually start seeking the zero position. If position loss must be expected, e.g. caused by manual user intervention, they repeat this on every new action.
In industrial robotic applications, the step counting and zero referencing is supplemented with an optical encoder and additional sensors and switches for fault detection.
the sensor for feed back is sometimes usefull, but actually we can change this kind of sensor using physical limit (usually in our mechanical design).
we able to design the working area of our stepping motor, suppose just 1 rotation (so we can't do more than 360 deg movement) or we can make 10 rotation for working range, and we can't exceed this.
during our initialisation, for the first time on, then we can forced the stepping motor move to the zero point (we can choose max or min point in the physical limitation). we able to do this using timer (we must calculate it, it depend on the working area of stepping motor), then after timer is complete we can assume that the stepping motor already at zero point. then we can move it according to our need and saved the last point position.
this kind of design is not robust (not good), it's possible that during the initialisation there is some disturbance, but this system is very simple, no sensor needed.
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