Constraints used between part symbols frequently model the mechanical attachment techniques used to connect the parts. These parts interact in a limited number of ways. The interaction of these part ports, the way in which each part can move with respect to the other part, is defined by joints.
In three-dimensional space, there are six degrees of freedom: X, Y, Z, RX, RY, and RZ. A joint restricts the motion of parts with respect to each other in one or more of these degrees of freedom. By using joints, you do not have to specify individual constraints. However, you do need to specify the joint type, the part ports to join, and the required port geometry. For example, for the revolute joint shown, you need to specify the joint type (revolute), the pipe and turnbuckle ports to join, and the port axis of rotation for the joint (X-axis).
You can define more than one joint per port connection as long as the joints do not conflict with one another.
Some common joints are shown in the pictures below.
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Revolute Joint |
Cylindrical Joint |
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Prismatic Joint |
Planar Slot Joint |
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Plane Joint |
Translation Joint |
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PointOnAxis Joint |
GlobalAxisAligned Joint |
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Rigid Joint |
PointOnPlane Joint |
The next table lists joint and coupling types along with the associated degrees of freedom and a description of each joint.
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Joint or Coupling Type |
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Revolute |
1) Axis 2) Origin (implied) |
1) No 2) No |
0 |
1 |
Objects spin about provided axis but do not translate. |
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Planar |
Plane |
Yes |
2 |
1 |
Objects free to rotate and translate while provided planes remain flush. |
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Translation |
1) Plane 2) Axis (in specified plane) |
1) Yes 2) No |
2 |
0 |
Objects may translate but NOT rotate while provided planes remain flush. |
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Prismatic |
1) Plane 2) Axis (in specified plane) |
1) Yes 2) Yes |
1 |
0 |
Objects may slide along provided axis but NOT rotate about the axis. |
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Rigid |
1) Plane 2) Axis (in specified plane) 3) Origin (implied) |
1) Yes 2) Yes 3) Yes |
0 |
0 |
Objects are rigidly fixed relative to each other. |
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Angular Rigid |
1) Plane 2) Offset 3) Rotation |
1) Yes 2) Yes 3) Yes |
0 |
0 |
Objects are rigidly fixed relative to each other at a specified angle. |
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Spherical |
Origin (implied) |
No |
0 |
3 |
Object origins remain in contact with each other while objects are free to spin. |
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Cylindrical |
Axis |
Yes |
1 |
1 |
Objects are free to spin about and translate along provided axis. |
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Planar Slot |
1) Plane 2) Axis (one object only) |
1) Yes 2) Yes |
1 |
1 |
While provided planes remain flush, the first point is on an axis of the second port. |
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GlobalAxisAligned |
Axis/Plane (one object, world Y- axis implied for other) |
No |
n/a |
n/a |
Axis is made parallel to vertical axis; plane is forced to contain vertical axis. |
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PointOnPlane |
1) Port Origin |
1) No |
1 DOF) if Geometry Type is an Axis. |
3 DOF |
The Origin of geometry 1 is located on geometry 2. It can translate and rotate as long as the origin remains on geometry 2. When using the Configuration Index Calculator, Geometry Type A refers to Input Geometry 2. |