tailieunhanh - Advanced Welding Processes Episode 2 Part 8

Tham khảo tài liệu 'advanced welding processes episode 2 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Monitoring and Control of Welding Processes 265 Direct control implies the measurement and feedback of the parameter which it is sought to regulate. For example in the case of a power source the current may be regulated by monitoring its output level as described in Chapter 3. Unfortunately in many welding situations it is not possible to use direct control and indirect systems based on the measurement of secondary variables must be used. Several indirect control systems will be described below but typical examples are weld bead temperature for penetration control and dynamic resistance for resistance spot weld geometry. The term adaptive control is often used to describe recent advances in welding process control but strictly this only applies to systems which are able to cope with dynamic changes in system performance 213 . Adaptive systems should have the ability to self-adjust in accordance with unpredictable changes in operating conditions. It has been pointed out 214 that in welding applications the term adaptive control may not imply the conventional control theory definition but may be used in the more descriptive sense to explain the need for the process to adapt to the changing welding conditions. Learning control systems are systems which progressively improve their performance by experience the most common example is the human operator but computer-based learning systems are being developed for welding applications. Basic requirements for closed-loop control For successful closed-loop control in welding appropriate feedback signals must be obtained these must be related in some way to the parameter to be regulated. A suitable error signal must be generated and the system must be able to respond to the required correction. The feedback signals may be obtained by monitoring the normal welding parameters or by employing sensors or transducers which supply indirect data. The relationship between the output and the control parameters may be defined by