Almost all the mechanisms used in the industry are single-movable. They are based on a kinematic chain with one degree of freedom with one input. The single-movable mechanism has an one-to-one correspondence of input and output parameters. The possibilities of the mechanism will be greatly expanded if it has two degrees of freedom. A definable twomovable kinematic chain with a single input will undoubtedly have fundamentally new properties. Many inventors have tried to use such a kinematic chain to create a stepless continuously variable transmission CVT [1, 2, and 3]. However, these attempts were unsuccessful due to the lack of definability of motion. According to the basic principles of mechanics, a mechanism with two degrees of freedom with one input cannot exist, since the kinematic chain of such a mechanism does not have the definability of motion, when the speed of the output link uniquely corresponds to the speed of the input link [4, 5]. The aim of the work is to prove the possibility of creating a definable two-movable kinematic chain with one input. The article performs kinematic and force analysis and provides proof of the theorem on the definability of motion of the simplest two-movable kinematic chain with one input. A definable two-movable kinematic chain with one input is the basis for the creation of a new class of mechanisms with two degrees of freedom, which have the property of force adaptation to a variable load.

Keywords: Theorem on the definability of motion, Two-movable kinematic chain with a single input, Substituting torque, Class of two-movable mechanisms