A Survey of Automated Threaded Fastening

Threaded fasteners are prevalent throughout modern manufacturing. Thus, as the demand for automation in manufacturing increases, so does the demand for automated threaded fastening systems. However, many fundamental issues and engineering challenges still hinder robustness in automation, particularly for smaller screws and critical product finishing requirements. This paper surveys the state of the art in threaded fastening automation and discusses open questions for further research. This survey covers the following areas: 1) fundamentals of threaded fastening, including basic concepts and definitions; 2) analysis of the entire assembly process (consisting of part feeding and orientation, pickup, alignment, and driving), including discussions of tools, control strategies, and other considerations; 3) failure modes and techniques to mitigate them; 4) threaded fastening systems and electromechanical approaches; and 5) open challenges and suggestions for future development. Understanding the current state of automation in threaded fastening will provide a foundation for researchers to advance this field. Note to Practitioners—This paper is motivated by the problem of an automated assembly of small screws, one of the most challenging problems in a smartphone assembly. It represents a rigorous review of robotic screwdriving literature to identify the state-of-the-art and open problems. The review material was targeted toward engineers working on related problems with the sponsor and has proved useful to them. To benefit researchers in the field of robotic and automated assembly, we have compiled the review material in the form of a survey paper. This paper covers theoretical fundamentals, tools, control and failure detection strategies, industrial applications, and open problems for robotic screwdriving. It provides a foundation for readers to familiarize themselves with the state of the art and conduct further research on this thread.

I. Introduction

Threaded fastening is one of the most prevalent assembly methods in manufacturing [1]. This method is often used when future disassembly is required for maintenance or rework [2]. Moreover, screws are the only fasteners that provide continuously variable joint tension by adjusting the tightening torque, which adds to their versatility [1]. In the late 1970s, Nevins and Whitney [3], [4] found that threaded fastening is constituted 27% of typical assembly tasks over a range of common products and second only to peg-in-hole assembly at 33%. In 1995, a survey of 24 product lines is classified 37.9% of all mechanical assembly operations as screw and bolt insertions [5]. Given its ubiquity, threaded fastening is an attractive target for automation.