Measurement and characterization of precision spherical joints

• Published in: Precision engineering Vol. 30; no. 1; pp. 1 - 12
• Main Authors: Robertson, Alec P., Slocum, Alexander H.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 2006; Elsevier Science
• Subjects: Applied sciences; Calibration; Drives; Exact sciences and technology; Linkage mechanisms, cams; Mechanical engineering. Machine design; Metrology; Parallel kinematic machines; Precision engineering, watch making; Spherical joint; SVD; HTM; CMM; PKM; Spherical joint; Metrology; DOF; Parallel kinematic machines; Calibration; Measurement; Spherical mechanism; Error estimation; Precision engineering; High precision; Parallel mechanism; Mechanical joint; Modeling; Load capacity; Navier Stokes equation; Kinematics; Linkage mechanism; Flat plate; Rolling sliding contact; Mechanical contact; Gas bearing; Ball joint; Joint; Experimental study; Externally pressurized gas lubrication; Measurement method; Measurement accuracy
• ISSN: 0141-6359; 1873-2372
• DOI: 10.1016/j.precisioneng.2005.01.001

Spherical joints based on a ball and socket configuration have been developed for parallel kinematic machines. Four prototypes are implemented using point, rolling, sliding and aerostatic contact mechanisms; each with a magnetic preload between the ball and the socket. A spherical kinematic test mechanism has been constructed to automate the measurement of joint accuracy, revealing a mean positional error of 3–5  μ m and a maximum positional error of 12–22  μ m for the joint prototypes. The flow properties of the aerostatic contact joint are modeled using a Navier–Stokes flat-plate approximation and found to be accurate to within 10% for a 20  μ m air gap. The tensile load capacity is 50–100 N rendering these joints suitable for high accuracy non-contact applications, such as inline measurement and inspection.