AC servo motors and step motors both have their own advantages and disadvantages. Here are some key differences between the two:

1. Control: AC servo motors use feedback control systems to achieve high precision and accuracy, while step motors operate in an open-loop control system that may result in less precision.

2. Torque: AC servo motors deliver higher torque at high speeds, while step motors deliver higher torque at low speeds.

3. Speed: AC servo motors can achieve faster speeds and acceleration due to their high response times and low inertia, while step motors have slower acceleration and maximum speeds.

4. Complexity: AC servo motors require more complex control systems, including encoders and feedback devices, while step motors have simpler control systems that can be driven by a simple controller.

5. Cost: AC servo motor systems are generally more expensive than step motor systems due to their higher complexity and advanced control systems.

Overall, the choice between AC servo motors and step motors depends on the specific application requirements and performance needs of the equipment.