A mechanism is described for effecting movement of an object, article or device in a closed loop planar path while maintaining the major axis of the object, article or device in substantially fixed attitude in the execution of at least an appreciable portion of the path, the mechanism comprising a six-bar linkage the dimensions of which are derived from a four-bar linkage to ensure the fixed attitude motion during motion through at least the appreciable portion of the closed loop path. A method of designing such a linkage mechanism comprises selecting a set of a finite number of discrete points around an idealized version of the closed path, at which points precise positioning and/or movement of the object is required to take place, establishing the dimensions of a four- bar linkage which will generate a synthesized path passing through the said selected precision points and deviating from the idealized path, if at all, by only an acceptable amount, and deriving from this four-bar linkage the dimensions of a six-bar linkage which will cause the required fixed attitude motion in the synthesized path.
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