Joint

Model Element

Class Name

Joint

Description

Joint is used to create an idealized connector between two bodies.

Joint defines a set of lower pair constraints. Physically, the joint consists of two mating surfaces that allow relative translational and/or rotational movement in certain specific directions only. The surfaces are abstracted away, and the relationships are always expressed as a set of algebraic constraint equations between points and directions on two bodies.

Attribute Summary

Name	Property	Modifiable by command?
id	Int ()
label	Str ()	✓
i	Reference (Marker)	✓
j	Reference (Marker)	✓
type	Enum (Type, default= "SPHERICAL", required=True)
pd	Double ()	✓
pitch	Double ()	✓
ic	Double (None, count=2)
ictran	Double (None, count=2)
icrot	Double (None, count=2)
active	Bool ()	✓

* Type=("CONVEL",”CYLINDRICAL","FIXED",HOOKE",PLANAR","RACKPIN",REVOLUTE","SCREW","SPHERICAL", "TRANSLATIONAL","UNIVERSAL")

Usage

Joint (i=objmarker, j=objmarker, type=string_joint_type, optional_attributes)

Attribute Description

Reference to an existing Marker

It specifies a Marker that defines the connection on the first body. The body may be a rigid body, a flexible body, or a point mass body.

This attribute is required.

Reference to an existing Marker

It specifies a Marker that defines the connection on the second body. The body may be a rigid body, a flexible body, or a point body.

This attribute is required.

type

String that is one of ("CONVEL", "CYLINDRICAL", "FIXED", "HOOKE", "PLANAR", "RACKPIN", "REVOLUTE", "SCREW", "SPHERICAL", "TRANSLATIONAL", "UNIVERSAL")

Specifies the type of constraint connection between the i and the j Markers.

This attribute is required.

Integer

Specifies the element identification number. This number must be unique among all the Joint objects in the model.

This attribute is optional. MotionSolve will automatically create an ID when one is not specified.

Range of values: id > 0

label

String

Specifies the name of the Joint object.

This attribute is optional. When not specified, MotionSolve will create a label for you.

pitch

Double

Defines the pitch for a screw joint. The pitch defines the ratio between the translational and rotational motion in the screw joint.

The attribute is mandatory when type="SCREW". It must not be specified otherwise.

Valid range of values: pitch > 0

Double

Defines the pitch diameter for the pinion gear of a rack and pinion gear joint.

The attribute is mandatory when type="RACKPIN". It must not be specified otherwise.

Valid range of values: pd > 0

List of two doubles

Specifies the initial velocity and initial displacement on either a translational or revolute joint.

This attribute may be optionally specified only when type="REVOLUTE" or type=”TRANSLATIONAL”.

ic expects two numeric values.

ictran

List of two doubles

Specifies the initial translational velocity and initial translational displacement of the cylindrical joint.

This attribute may be optionally specified only when type="CYLINDRICAL".

ictran expects two numeric values.

icrot

List of two doubles

Specifies the initial rotational velocity and initial rotational displacement of the cylindrical joint.

This attribute may be optionally specified only when type="CYLINDRICAL"

icrot expects two numeric values.

active

Bool

Select one from True or False.

•	True indicates that the element is active in the model and it affects the behavior of the system

•	False indicates that the element is inactive in the model and it does not affect the behavior of the system. It is almost like the entity was removed from the model, of course with the exception that can be turned “ON” when desirable.

The attribute active is optional. When not specified, active defaults to True

Comments

1.	See Properties, for an explanation about what properties are, why they are used and how you can extend these.

2.	Use the Jprim (…) method to define a Joint Primitive modeling element with this API. The following joint types in the XML syntax are considered to be joint primitives:

•	"INLINE”, “INPLANE”, “ORIENTATION”, “PARALLEL_AXES”, “PERPENDICULAR”, “PLANAR"

3.	For a more detailed explanation about Joint, see the Comments in the XML syntax section.

Examples

1.	Create a cylindrical joint between bodies p3 and p4.

Location specified by an existing point, pc

Z-axis along global x-axis

zpval = pc + Vector(1,0,0)

p3.C = Marker (body=p3, qp=pc, zp=zpval, label="p3.C")

p4.C = Marker (body=p4, qp=pc, zp=zpval, label="p4.C")

jcyl = Joint (i=p4.C, j=p3.C, type="CYLINDRICAL", label=”Joint #1”)

2.	Add an initial translational velocity & displacement to an existing cylindrical joint jcyl.

jcyl.ictran = (3.142, 2.71828)

3.	Create your own simple function to create a cylindrical joint and use it.

#Define the function first

def CylindricalJoint (ibody, jbody, location, axis, label, **kwds):

"""

ibody - A rigid body, point mass or flex-body

jbody - A rigid body, point mass or flex-body

location - A Point

axis - A Vector

label - A name for the joint

"""

#Coordinates of a point along the axis of rotation

zpval = location + axis

i = Marker (body=ibody, qp=location, zp=zpval)

j = Marker (body=jbody, qp=location, zp=zpval)

jcyl = Joint (type="REVOLUTE", i=i, j=j, label=label, **kwds)

i.label = label + " I Marker"

j.label = label + " J Marker"

return jcyl

#Create a cylindrical joint using the convenience function described above

pc = Point (23.1, -46.2, 69.3*math.sin(0.436332))

zaxis = Vector(1,0,0)

label = “Joint #1”

jcyl = CylindricalJoint (p3, p4, pc, zaxis, label, ictran=(3.142, 2.71828))

4.	Create a joint and then define a displacement Request between its I and J markers.

#Define the joint

pc = Point (23.1, -46.2, 69.3*math.sin(0.436332))

zaxis = Vector(1,0,0)

label = “Joint #1”

jcyl = CylindricalJoint (p3, p4, pc, zaxis, label, ictran=(3.142, 2.71828))

#Now define the request

comment = jcyl.label + ” Displacement”

r1 = Request (type="DISPLACEMENT", i=jcyl.i, j=jcyl.j, comment=comment)

5.	Using the “dot” operator to “get” the attributes of a joint.

Assume that a joint object has been created using the first example.

jcyl = Joint (i=p4.C, j=p3.C, type="CYLINDRICAL", label=”Joint #1”)

The dot operator may be used as shown below to get the attributes for a joint:

iMarker = jcyl.i # The I marker for the joint jcyl

jtype = jcyl.type # The type of the joint jcyl

iBody = iMarker.body # The body to which iMarker belongs

iMass = iBody.mass # The mass of the body to which the iMarker belongs