Methods that help operators avoid errors caused by choosing the wrong part, omitting a part, installing a part incorrectly and so on. Also called mistake-proofing, poka-yoke and baka-yoke .

Some common examples of error-free production: 

• Product designs with physical shapes that make it impossible to install parts the wrong way.
  
• Photocells above parts containers to prevent a product from moving to the next step if the operator's hands have not broken the light to grab the necessary parts.
  
• A more complex component monitoring system that also uses photocells, but has additional logic built in to ensure that the correct combination of components is selected for the specific product being assembled.

An example of a contact-based error-free manufacturing tool: