1992 Volume 10 Issue 4 Pages 490-495
This paper deals with some problems concerning the sensing and controlling of the weld pool. A good quality of the welding result can be obtained by keeping the weld pool shape constant. The system for sensing and controlling the weld pool is proposed.
First, authors tried to take an image of the weld pool with a CCD shutter camera. A new method is proposed to clearly take the weld pool. The method is to reduce the welding current as small as possible while the shutter of the CCD camera opens for 1 [ms]. The weld pool shape can be obtained by the image processing.
Next, the method is discussed for controlling the weld pool. It may be difficult to describe the state equations of the weld pool shape, since welding phenomena are described by partial differential equations. Therefore, authors control the weld pool shape with the fuzzy controller. In fuzzy control, it is important to determine the control rule and the fuzzy variables. A new method is proposed for designing the fuzzy controller.
The weld pool width w (t) for the welding current u(t) is approximated by a first order system with the time delay T : dw(t)/dt=-λw(t)+bu(t-T).
In the system with the time delay, when the gain of the conventional fuzzy controller increase, the response of the plant may become unstable. In order to improve the control performance, the fuzzy variables and the control rules are constructed from design knowledge of the controller for the first order system with the time delay. Namely the deviation e[n], its variation Δe[n], the prior manipulating variable Δu[n-1], and the manipulating variable Δu[n] are used as the fuzzy variables. The validity of proposed method was verified by the experiments.