The application of robotics to the assembly of flexible parts by sewing

Abstract

This thesis concerns the development of a robotic cell to
\nperform assembly and handling operations on cloth.- A
\nflexible automation approach was adopted, in which the
\nrobot was required to control the cloth panel during both
\nhandling and sewing operations, without the aid of hard
\nautomation attachments which might limit the flexibility of
\nthe system. The cell consisted of an adaptively controlled
\nrobot, a hierarchy of controllers, a conventional sewing
\nmachine, a two-fingered fabric steering end-effector, and
\nseveral sensor systems.
\nA technique was developed for producing a seam parallel to
\nan edge of arbitrary contour, in which two cameras, a
\ncloth tension sensor and the sewing machine's shaft encoder
\nprovided the sensory input. Two sensory servo control
\nsystems were required, one control system generated the
\nrobot's trajectory to maintain a small constant cloth
\ntension, and the other directed the robot to manipulate the
\ncloth panel to maintain a constant seam width.
\nThe design of the cloth tension control was based on the
\nmeasured frequency response of the open loop system. The
\nseam width control was designed using simulation studies,
\nwhich accounted for the control transfer function, and nonlinearities
\nsuch as camera pixel resolution, time delays
\nand robot motion limitations.
\nSeveral robotic handling techniques were developed, so that
\na cloth panel placed arbitrarily on the sewing table could
\nbe set up for an edge seaming operation, and the cloth
\ncould be rotated about the needle. The system's flexibility
\nwas demonstrated in the assembly of an irregularly shaped
\ncloth panel, in which three adjacent sides were sewn up.
\n