Ohjautuvuuden

Ohjautuvuuden, the Finnish term for controllability, refers to the ability of a system to be guided or steered by external inputs. In engineering contexts, it denotes whether the states of a dynamic system can be driven from one configuration to another within finite time using admissible inputs. In everyday language, it is sometimes used as drivability, especially in vehicle dynamics, to describe how a vehicle responds to steering commands.

In control theory, ohjautuvuus is a property of a model described by differential equations. For a linear time-invariant system x' = A x + B u, the system is controllable if the controllability matrix [B AB A^2B ... A^{n-1}B] has full rank n. The Kalman criterion provides a practical test. Controllability is dual to observability.

For nonlinear systems, the concept is extended by conditions such as the Lie algebra rank condition, using Lie brackets of vector fields to assess local controllability, and the notion of accessibility.

In vehicle dynamics, ohjautuvuus influences how well a car or robot can follow a desired trajectory under actuator limits, tire friction, and disturbances. Factors include steering actuator authority, tire-road interaction, and vehicle inertia. Modern systems use electronic control units to enhance controllability through feedback and redundancy, e.g., drive-by-wire, stability control.

In design and analysis, engineers assess controllability to ensure reachability of required states, to achieve robust performance, and to detect potential faults or constraints that could hinder control. Limitations include model inaccuracies, actuator saturation, and environmental disturbances, which can reduce effective controllability even if a mathematical model is controllable.

The term is used in Finnish research and industry to discuss the property of systems to be steered or controlled, spanning mechanical engineering, robotics, and automation. While the mathematical notion is precise, practical ohjautuvuus is judged by achievable performance under real-world constraints.