The Screw Fastening Unit is the most important mechanism of the automated screw fastening device. The representative screw fastening methods and examples of the fundamental structure of automated devices are introduced here.

(1)Screw Fastening Methods

The representative structure of screw fastening unit is as follows.

There are following screw fastening methods for the screw fastening units. Variations of the fastening forces can be improved in the order as a>b>c {high accuracy}.

	a) Torque Control Method	： A method of transmitting the power of electric motor to the shaft of the screw fastening unit as rotational torque.
	b) Angular Control Method	： A method of controlling the screw tightening angle with motors with angular encoders.
	c) Yield Point Method	： A tightening force control method by detecting the deformation behavior of tightened screws.

(2)Example of a screw fastening unit

[Fig.1] is an example of an automated nut fastening device with 6 axes of parallel equipped pneumatically operated nut fastening actuators (nut runner). Nuts are tightened after the 6 axis nut fastening actuators are moved by the cylinder on linear guides.