Use of the Split Kinematic Vee Block

There are frequent problems with “off balance” in conventional kinematic couplings. This is particularly true of large structures. The platforms for most kinematic couplings are rectangular, but the kinematic coupling forms a three point tripod of contacts. If off center loads are applied to the conventional kinematic platform, it can become unstable, even to the point of tipping out of contact. This dilemma can be addressed by using the split kinematic coupling design. A conventional “Maxwell” kinematic coupling consists of three vee blocks in contact with three spheres, to constrain all six degrees of freedom. Two conventional vee blocks should be located very near two adjacent corners, of one platform with their axii aimed at the centroid of the rectangle. If we applied some thought to this design, it becomes obvious that the spacing between the two prismatic surfaces, of one of the vee blocks could be widely separated, without altering the overall performance of the kinematic system.

By taking a similar approach to the sphere, two small sections of a large sphere, could be used to provide the two points of spherical constraint required. If we use any the standard Giant Spherical Components with 40 inch (1.00 meter) diameter spherical surfaces, the distance between the two points of spherical contact would be 20 inches or one half of a meter. If this separation of the prismatic faces of the Vee block is used, there will be perfectly kinematic contact without any of the effects of Abby offset. If this perfect situation can’t be achieved exactly, only small errors in repeatability will occur for larger or smaller separations of the prismatic surfaces of the vee’s, as long as the deviation in the separation is not too severe. The split vee blocks can be mated with any of our “Giant Spherical Components.” The term giant refers to the spherical radius not the physical size of the components. [See Giant Spherical Components in our web catalogue on his site].

Another approach that is simple in construction is to use one of the spherical surfaces of a Cylindrical Post Mounted Canoe sphere, our part number 2000-CS, against the prismatic face of a split Vee Block. The cylindrical post, makes the mounting of the component parts simple. Another capability of the split vee block is to use it as a male vee block with a Giant or small Spherical contact on each side. This approach is very powerful in situations where linear adjustability is required. The opposite alternative to use one of the one inch (1.00”) [25.4mm] diameter kinematic components against one or another of the split kinematic designed parts.

Cheating

I love to cheat the system a little, when I can get away with it! When you can break the laws of physics, or at least give them a good bend and walk way scott-free, it is a warm sunny day. When coupling two bodies together, with a high degree of accuracy, three points of contact, or the “tripod rule” is a marvel, but in a rectilinear world, three equilateral points of contact, don’t match the rectangular parts. The problem gets even worse when the aspect ratio of the mounting platform, doesn’t lend itself to an equilateral three point, coupling design.

By using a pseudo Maxwell kinematic system, that basically consists of two standard Vee Blocks and one split vee block with four mating spheres, you get a perfectly functional kinematic coupling, that has the much more stable, four legs of support. We produce a broad line of standard off the shelf Vee Blocks and Vee Block like products. We also produce several unique, off the shelf, split vee blocks.

The technical aspects of using the split kinematic technique have been published by Dr. Alex Slocum of M.I.T. as well as by our company (See the list of technical papers on our website www.precisionballs.com).

See our page, "Giant Split Vee Block" for more information about the vee block.

See our page, All Vee Blocks, for pricing information.