Kinematics equations are the constraint equations of a mechanical system such as a robot manipulator that define how input movement at one or more joints specifies the configuration of the device, in order to achieve a task position or end-effector location. Kinematics equations are used to analyze and design articulated systems ranging from four-bar linkages to serial and parallel robots. Kinematics equations are constraint equations that characterize the geometric configuration of an articulated mechanical system. Therefore, these equations assume the links are rigid and the joints provide pure rotation or translation. Constraint equations of this type are known as holonomic constraints in the study of the dynamics of multi-body systems.
Loop equations The kinematics equations for a mechanical system are formed as a sequence of rigid transformations along links and around joints in a mechanical system. The principle that the sequence of transformations around a loop must return to the identity provides what are known as the loop equations. An independent set of kinematics equations is assembled from the various sets of loop equations that are available in a mechanical system.
Transformations In 1955, Jacques Denavit and Richard Hartenberg introduced a convention for the definition of the joint matrices [Z] and link matrices [X] to standardize the coordinate frames for spatial linkages. This convention positions the joint frame so that it consists of a screw displacement along the Z-axis
[ Z i ] = [ cos θ i − sin θ i 0 0 sin θ i cos θ i 0 0 0 0 1 d i 0 0 0 1 ] , {\displaystyle [Z_{i}]={\begin{bmatrix}\cos \theta _{i}&-\sin \theta _{i}&0&0\\\sin \theta _{i}&\cos \theta _{i}&0&0\\0&0&1&d_{i}\\0&0&0&1\end{bmatrix}},}
and it positions the link frame so it consists of a screw displacement along the X-axis,
[ X i ] = [ 1 0 0 a i , i + 1 0 cos α i , i + 1 − sin α i , i + 1 0 0 sin α i , i + 1 cos α i , i + 1 0 0 0 0 1 ] . {\displaystyle [X_{i}]={\begin{bmatrix}1&0&0&a_{i,i+1}\\0&\cos \alpha _{i,i+1}&-\sin \alpha _{i,i+1}&0\\0&\sin \alpha _{i,i+1}&\cos \alpha _{i,i+1}&0\\0&0&0&1\end{bmatrix}}.}
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