Abstract
This review focuses on the need for, challenges to, and means of achieving effective control in resistance spot welding; beginning with the earliest single variable open loop systems, progressing to single-, then multivariable feedback and adaptive closed loop systems. The former applied a control action to a single input variable to compensate for drops in line voltage without assessing the effect on output online. The latter use feedback of either single or multiple output variables measured online to execute a preplanned control action, with adaptive systems able to selfadjust gains and/or time constants in the control law in accordance with predictable and unpredictable variations to achieve near constant output. The capabilities and shortcomings of each approach are addressed. The review ends with a discussion of emerging systems for achieving intelligent control by comparing inputs against outputs of actual versus ideal welds and executing control commands in real time based on process knowledge and learning.
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