Step 1: Robot generation classification.
- First generation: Simple mechanical arms, programmed to perform repetitive tasks.
- Second generation: Equipped with sensors for feedback.
- Third generation: Advanced robots with adaptive learning.
- Fourth generation: Intelligent robots with AI.
Step 2: Identify the category.
A simple mechanical arm falls under the first generation, as it lacks sensors and advanced intelligence.
Final Answer: \[ \boxed{\text{First generation}} \]