Kinematic analysis / multibody simulation (MBS)
In the product development of moving systems, determining the loads needed to size individual components can be highly complex. This may be due to the sheer number of load cases to be calculated, or to complicated kinematic relationships.
Kinematic analysis makes it possible to determine the loads occurring in operation on the computer at a very early stage of development. The kinematics can be examined and optimised with respect to collisions and to the forces and moments that arise. If flexible components are used in the simulation, the resulting stresses and deformations can be determined and evaluated directly.
The main simulation options are listed below:
Rigid-body kinematics
Analysing a system with rigid-body kinematics is the simplest form of kinematic analysis. Here the individual components are treated as rigid bodies. Each body is assigned its centre of gravity position along with its mass and inertia properties. Joints are defined at the kinematic points, connecting the components with specified degrees of freedom. Loads such as motions, forces or accelerations can be applied in the analysis. The result is a range of response quantities over time — for example displacement, velocity, acceleration or force.
These results can then be used as loads in a strength analysis.
Flexible kinematics
The stiffness of individual components in a kinematic system can have a major influence on the results — in some cases it is decisive for how the system functions. To account for stiffness in the simulation, the relevant components are defined as flexible bodies. Using flexible bodies in kinematic simulation is essential for systems with redundant constraints.
In addition to the results listed for rigid-body kinematics, the analysis then also yields stresses and strains over time. These can be evaluated directly with respect to static and dynamic strength.
Co-simulation
Co-simulation makes it possible to simulate the interaction between a controller (e.g. a PLC) and the mechanics. The controller is modelled in a system simulator such as Matlab/Simulink. Its input and output channels are coupled directly to the simulation model. The controller then supplies the control signals to the multibody simulation model and thus moves the components. The resulting motions (displacements, velocities and accelerations) are fed back to the virtual controller.
Beyond representing the kinematics, the aim of such an analysis is to optimise the control parameters before a physical prototype exists. This can dramatically speed up real-world commissioning.
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