Design of quasi-kinematic couplings

• Published in: Precision engineering Vol. 28; no. 3; pp. 338 - 357
• Main Author: Culpepper, Martin L
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.07.2004; Elsevier Science
• Subjects: Applied sciences; Assembly; Automotive assembly; Exact constraint; Exact sciences and technology; Fixture; Kinematic coupling; Mechanical engineering. Machine design; Over constraint; Photonics; Plastic deformation; Precision engineering, watch making; Precision optics; Quasi-kinematic coupling; Repeatability; Stiffness; Kinematic coupling; Repeatability; Over constraint; Exact constraint; Quasi-kinematic coupling; Precision optics; Automotive assembly; Stiffness; Plastic deformation; Fixture; Assembly; Photonics; Experimental study; Clamping; Work holder; Sealing; Axial symmetry; Contact surface; Kinematics; Groove
• ISSN: 0141-6359; 1873-2372
• DOI: 10.1016/j.precisioneng.2002.12.001

A quasi-kinematic coupling (QKC) is a fixturing device that can be used to make low-cost assemblies with sub-micron precision and/or sealing contact. Unlike kinematic couplings that form small-area contacts between mating balls in v-grooves, QKCs are based on arc contacts formed by mating three balls with three axisymmetric grooves. Though a QKC is technically not an exact constraint coupling, proper design of the contacts can produce a weakly over constrained coupling that emulates an exact constraint coupling. This paper covers the practical design of QKCs and derives the theory that predicts QKC stiffness. A metric used to minimize over constraint in QKCs is presented. Experimental results are provided to show that QKCs can provide repeatability (1/4 μm) that is comparable to that of kinematic couplings.