There are five primary reasons why stepper motors are rarely adopted in industrial robots:

Stepper motors operate at low rotational speeds with limited torque, restricting the maximum rated payload at the robot end effector.

Stepper motors offer low positioning accuracy and are prone to step loss. The serial-link structure of industrial robots inherently generates cumulative errors. Using stepper motors further degrades absolute accuracy to a level inadequate for most industrial applications.

Speed regulation of stepper motors relies on pulse frequency. They exhibit poor low-speed response and are susceptible to stall.

High operational noise.

Stepper motors cannot implement closed-loop position sensing. The controller lacks real-time position feedback for each robot joint, which means homing calibration is mandatory every time the system powers on.

Nevertheless, stepper motors have their merit: low cost. The total cost can be further reduced when reducers are not required. Therefore, they are well suited for applications with relaxed requirements on accuracy, payload and noise.