Stepper Motor Driving

Stepper motor is operated by pulses:

• Typically runs by two signals: step pulses and direction
• There is a small transient motion at each step

Stepper motor is operated in discrete mode:

• The load torque results in some position error

Stepper Motor Torque-Speed Curve

Totally different from servo motors (DC, BLDC):

• Torque drastically decrease as speed increases
• Typical speed ranges from 100 to 1000 rpm
• Difficult to establish distinct rated torque or speed

Example: Stepper Motor Selection

From the velocity profile:

$$\begin{array}{rl}d& =\frac{1}{2}{v}_{\text{max}}t\\ v_{\text{max}}& =\frac{2d}{t}=\frac{2\times 0.1}{0.2}=1\text{ m/s}\end{array}$$

Max acceleration/deceleration:

$$\alpha =\frac{v_{\text{max}}}{t/2}=\frac{1}{0.2/2}=10{\text{ m/s}}^2$$

Angular acceleration/deceleration:

$$\alpha =\frac{a}{r}=\frac{10}{0.05}=200\text{ rad/s}=191\text{ rpm}$$

Require motor torque:

$$T_m=J\alpha =(J_{\ell }+J_m)\alpha$$

Note that $J_m$ is very small compared to $J_{\ell }$, so it can be ignored. Thus, we have:

$$T_m=J_{\ell }\alpha =0.01\times 200=2\text{ Nm}=283\text{ oz-in}$$

From the torque-speed curve (pull-out torque):

Model	Torque @ ${\omega }_{\text{max}}$
140 SM	142
310 SM	370
1010 SM	1050

Therefore, the 310 SM will be suitable.