Tech Briefs

Analysis of Robots

Traditionally the analysis of robots is performed using a hybrid approach, namely with multibody dynamics and motion analysis software. Flexibility effects are included separately, for example using flexible body integration.

Here we present some analyses of robots, in which the analyses are performed entirely within ADINA. The robot arms and grips are modeled with the large displacement solid and shell elements available in ADINA. Contact conditions are also included.

Using ADINA, the rigidity and flexibility of parts and of the entire system are directly modeled and included in a single analysis run, in which accurate stress results are obtained.

Shell element robot moving light block, inertial effects are very small

Shell element robot moving heavy block, inertial effects are considerable

A new development in ADINA, that allows the analysis of the complete robot as the robot moves through very large displacements and rotations, is the modeling of the joints using alignment elements. By prescribing the rotational orientations of the alignment elements, the robot motion itself is prescribed.

The animations show a robot arm assembly modeled using shell and solid elements. Dynamic conditions are assumed, and the Bathe method of time integration is used in the solution.

An exploded view of the assembly is shown below.

Each joint is modeled using rigid links and alignment elements, as shown:

The flexibility due to inertia effects is clearly visible when the robot manipulates the heavy block.

Also, the large displacement beam elements of ADINA can easily represent the large motions typical in robotic analysis. Rapid prototyping can be done with beam element models, because these are easy to set up and are very inexpensive to run. An animation of a robot modeled with beam elements is shown below.

Clearly the new alignment element in ADINA v. 8.9 is very powerful and offers many interesting modeling possibilities in engineering and the sciences. Modeling robots with the actual physical stiffnesses/flexibilities is just one field of application.

Robots, rigid body dynamics, flexibility, large displacements, finite elements, unified rigid-flexible analysis, contact, shells, beams, multiphysics, Bathe method