Gain Scheduled PID Force Control of a Robotic Arm for Sewing Fabrics

In this paper, a gain scheduled PID force feedback controller of a manipulator is designed and implemented for the robotized sewing of fabrics, using a commercial sewing machine. The proposed manipulator controller should keep a constant tension of the fabric, to achieve high quality of cloths seams, as the length of the fabric is shortened along the sewing process. For the controller design, a non-linear model of the fabric is considered, varying with the actual length between the grasping and sewing points. The model is based on a simplified Kelvin-Voigt model with non-linear spring and damper coefficients, which also depend on the type and the length of the fabric and are estimated experimentally. The Model-based PID tuning process from Simulink is used, for tuning and scheduling the gains of the PID controller corresponding to fabric’s different actual lengths. The determined sets of gains are used for controlling on-line an Adept Cobra s800 robot to manipulate a woven piece of fabric during the sewing process, where the proposed approach is tested. The proposed force control approach maintains a stable tensional force on the fabric and therefore the quality of the seam and hence of the cloth could be enhanced. Finally, it is compared with a PID controller with constant gains.