721
The layer-by-layer generation of optimized trajectories is validated experimentally on a 6-axis robot using a PLA extrusion system .
 concept or principle: layer-by-layer; machine or equipment: robot; material: PLA; manufacturing process: extrusion
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 concept or principle: layer-by-layer; machine or equipment: robot; material: PLA; manufacturing process: extrusion