Model: T04 Parallel Stage of von Schönemann

The T series in the Voigt catalog constitute so-called parallel guide mechanisms. In contrast with the straight-line mechanisms in the S series, the parallel guides maintain zero rotational variation between links during motion. The models T-3 to T-8 incorporate horizontal stages as in weighing machines. In model T-4 two lever mechanisms (a smaller one above the lower lever) are coupled by three vertical links as well as through a ground link at their fulcrums. This is an example of a compound kinematic chain. Grübler published a criterion to determine the degrees of freedom for a set of n links and v joints and number of degrees of freedom F=3(n-1)-2r (See KMODDL Tutorial on Mobility (Grübler’s) criteria.) In model T-4, there are 8 cylindrical joints and 6 links (counting the grounded link) which gives F=-1. Since F=1 constitutes a perfect mechanism, the arrangement in T-4 is more like a structure. The special vertical and horizontal link allows small motions that keep the two stages parallel. A similar over-constrained mechanism is shown in Model T-6.

Francis Moon 2004-07-00

#### Resources :

- Biography : Schönemann, Theodor