Point to Curve Library


Volker Beuter  : v.beuter@kaemmerer-group.com

Industry / Process

  •  Automotive
  •  General Machinery
  •  Mechanics

Short Description

The PointToCurve package has been developed for usage in Kämmerer's Cabrio Package. It provides abstract models of guidance elements, in particular a constraint model with one degree of freedom where one frame can move along a smooth curve fixed in the other frame. This has many applications far from convertible roof modelling and can rather be seen as an extension to the Modelica.Mechanics.MultiBody package.


Long Description

Kämmerer's Cabrio Package is build up with elements from the Modelica Standard Library MultiBody mechanics package. For models like a four bar this worked well but it turned out early that there are some elementary models missing. For a high level of detail guidance elements ought to be modeled by general 3D body contact elements calculating the contact forces between a pair of contacting geometries. But on the one hand such models are not yet available in the MSL, on the other hand 3D contact forces would be to time-consuming for many applications. When abstracting from backlash etc. a guidance element where some pin can move in some curved slot can be viewed as a point which can move along the center line of the slot, possibly with stops modeled by strong repulsive forces guaranteeing that the point does not leave an admissibly range.

Such models are available in the PointToCurve package. The curve may be 2D or 3D, open or closed (cyclic) and can be defined by using replaceable functions, splines from Kämmerer's Spline package or Bezier splines from a BSpline package developed at the DLR. Curves can be defined using Cartesian or Cylinder coordinates making it easy to define e.g. closed curves for modeling cam disks. The orientation of the point frame can be parallel to the curve frame or tangentially to the curve. PtCv joints can be equipped with stops modeled by impact forces consisting of a non-linear spring and a damping smoothly rising from zero at the moment of contact to full damping at a certain penetration depth. The package comes with a large number of test models.

Besides this there are some impact models which can be used to model contact forces between two spherical objects or a sphere and some (possibly bounded) contact plane. The moreover there is a contact force between a point and a single-curvature surface.

Release History

Release Date

Release ID

with Modelica


Tested with

October 14, 2009




Dymola 7.1

March 29, 2010




Dymola 6.1/7.1

February 26, 2010



Spline, Bspline, Visualizer

Dymola 6.1/7.1

June 2010



Spline, Bspline, Visualizer

Dymola 7.4

Download Materials



Paper for Modelica2009 conference

Paper for Modelica2009 conference, revised Edition



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