Abstract
Parallel robots are known to o er light, highly agile structures, particularly suited for assembly and machining tasks. By the same token, parallel robots pose unique challenges to the robot designer, in that a compromise must be found among the various requirements: large workspace with respect to footprint; high sti — ness; high natural frequencies; high mobility; and low cost, among others. Most parallel robots are designed with as many limbs as degrees of freedom (dof), which increases then- footprint and limits their dextrous workspace—that region of the workspace where the moving platform can undergo a full rotation. An alternative to these designs is a reduced number of limbs, lower than their dof, but this calls for limbs driven by two or more motors. The challenge here is to drive two axes in a serial array with two motors mounted on the base platform. This mode of driving has not received due attention from the robot-design community, but is worth exploring. Proposed in this paper is a qu sispheric l linkage intended to drive the tilt axis of one of the two limbs of a four-dof parallel robot, currently under development. The linkage is termed quasispherical in that it is nominally designed as a spherical four-bar linkage, but spherical linkages impose extremely tight tolerances to make them assemblable. A common alternative to tight tolerances is an increase in the degree of freedom of the linkage, upon replacing the passive revolutes by orientable pinned-joints, which are kinematically equivalent to spherical joints, thereby increasing unnecessarily the mobility of the linkage. This compromises the linkage sti ness, a major concern for e ective actuation. As an alternative, a linkage of the R type is proposed here, where R andstand for revolute and cylindrical joints. However, cylindrical joints are not that common as machine elements, besides being demanding in terms of tolerances, while o ering low sti ness. A realization of the joint is proposed here by means of a serial array of a R and a screw joint, labeled H.
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Angeles, J. (2010). Robust Drives for Parallel Robots. In: Parenti Castelli, V., Schiehlen, W. (eds) ROMANSY 18 Robot Design, Dynamics and Control. CISM International Centre for Mechanical Sciences, vol 524. Springer, Vienna. https://doi.org/10.1007/978-3-7091-0277-0_2
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