PrismaticWithLengthConstraint

Prismatic joint where the translational distance is computed from a length constraint (1 degree-of-freedom, no potential state)

    PrismaticWithLengthConstraint

Library

Modelica/Mechanics/MultiBody/Joints/Internal

Description

Joint where frame_b is translated along axis n which is fixed in frame_a. The two frames coincide when "s + s_offset = 0", where "s_offset" is a parameter with a zero default and "s" is the relative distance.

This variant of the prismatic joint is designed to work together with a length constraint in a kinematic loop. This means that the relative distance "s" of the joint is computed such that the length constraint is fulfilled.

Usually, this joint should not be used by a user of the MultiBody library. It is only provided to built-up the Modelica.Mechanics.MultiBody.Joints.Assemblies.JointXYZ joints.

In releases before version 3.0 of the Modelica Standard Library, it was possible to activate the force projection equation (= cut-force projected to the translation axis must be identical to the driving force of flange axis) via parameter axisForceBalance. This is no longer possible, since otherwise this model would not be "balanced" (= same number of unknowns as equations). Instead, when using this model in version 3.0 and later versions, the force in the length constraint component (Joints.SphericalSpherical or Joints.UniversalSpherical) must be calculated such that the driving force in direction of the translation axis is (RC shall be the name of the instance of PrismaticWithLengthConstraint):

    0 = RC.axis.f + RC.e*RC.frame_b.f;

If this equation is used, usually the force in the length constraint and the second derivative of the prismatic distance will be part of a linear algebraic system of equations. In some cases it is possible to solve this system of equations locally, i.e., provide the rod force directly as function of the prismatic constraint force. In any case, this projection equation or an equivalent one has to be provided via variable "constraintResidue" in the "Advanced" menu of "Joints.SphericalSpherical" or "Joints.UniversalSpherical".

Parameters

PrismaticWithLengthConstraint_0

NameLabelDescriptionData TypeValid Values

mo_animation

animation

= true, if animation shall be enabled

Scalar

true
false

mo_length

length

Fixed length of length constraint

Scalar

mo_n

n

Axis of translation resolved in frame_a (= same as in frame_b)

Vector of size 3

mo_s_offset

s_offset

Relative distance offset (distance between frame_a and frame_b = s(t) + s_offset)

Scalar

mo_s_guess

s_guess

Select the configuration such that at initial time |s(t0)-s_guess| is minimal

Scalar

mo_positiveBranch

positiveBranch

Selection of one of the two solutions of the non-linear constraint equation

Scalar

true
false

mo_e

e

Unit vector in direction of translation axis, resolved in frame_a

Vector of size 3

PrismaticWithLengthConstraint_1

NameLabelDescriptionData TypeValid Values

mo_boxWidthDirection

boxWidthDirection

Vector in width direction of box, resolved in frame_a

Vector of size 3

mo_boxWidth

boxWidth

Width of prismatic joint box

Scalar

mo_boxHeight

boxHeight

Height of prismatic joint box

Scalar

mo_boxColor

boxColor

Color of prismatic joint box

Vector of size 3

mo_specularCoefficient

specularCoefficient

Reflection of ambient light (= 0: light is completely absorbed)

Scalar

PrismaticWithLengthConstraint_2

NameLabelDescriptionData TypeValid Values

mo_position_a

position_a

position_a

Structure

mo_position_a/fixed

fixed

Cell of vectors of size 3

true
false

mo_position_a/start

start

Cell of vectors of size 3

mo_position_b

position_b

position_b

Structure

mo_position_b/fixed

fixed

Cell of vectors of size 3

true
false

mo_position_b/start

start

Cell of vectors of size 3

mo_s

s

s

Structure

mo_s/fixed

fixed

Cell of scalars

true
false

mo_s/start

start

Cell of scalars

mo_distance

distance

distance

Structure

mo_distance/fixed

fixed

Cell of scalars

true
false

mo_distance/start

start

Cell of scalars

mo_r_rel_a

r_rel_a

r_rel_a

Structure

mo_r_rel_a/fixed

fixed

Cell of vectors of size 3

true
false

mo_r_rel_a/start

start

Cell of vectors of size 3

mo_f

f

f

Structure

mo_f/fixed

fixed

Cell of scalars

true
false

mo_f/start

start

Cell of scalars

Ports

NameTypeDescriptionIO TypeNumber

frame_a

implicit

Coordinate system a fixed to the component with one cut-force and cut-torque

input

1

frame_b

implicit

Coordinate system b fixed to the component with one cut-force and cut-torque

output

1

axis

implicit

1-dim. translational flange that drives the joint

input

2

bearing

implicit

1-dim. translational flange of the drive bearing

output

2

position_a

implicit

Position vector from frame_a to frame_a side of length constraint, resolved in frame_a of prismatic joint

input

3

position_b

implicit

Position vector from frame_b to frame_b side of length constraint, resolved in frame_b of prismatic joint

input

4