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212 lines
8.7 KiB
ReStructuredText
212 lines
8.7 KiB
ReStructuredText
.. _joints:
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######
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Joints
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######
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:class:`~topology.Joint`'s enable Solid and Compound objects to be arranged
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relative to each other in an intuitive manner - with the same degree of motion
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that is found with the equivalent physical joints. :class:`~topology.Joint`'s always work
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in pairs - a :class:`~topology.Joint` can only be connected to another :class:`~topology.Joint` as follows:
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+---------------------------------------+---------------------------------------------------------------------+--------------------+
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| :class:`~topology.Joint` | connect_to | Example |
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+=======================================+=====================================================================+====================+
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| :class:`~joints.BallJoint` | :class:`~joints.RigidJoint` | Gimbal |
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+---------------------------------------+---------------------------------------------------------------------+--------------------+
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| :class:`~joints.CylindricalJoint` | :class:`~joints.RigidJoint` | Screw |
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+---------------------------------------+---------------------------------------------------------------------+--------------------+
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| :class:`~joints.LinearJoint` | :class:`~joints.RigidJoint`, :class:`~joints.RevoluteJoint` | Slider or Pin Slot |
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+---------------------------------------+---------------------------------------------------------------------+--------------------+
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| :class:`~joints.RevoluteJoint` | :class:`~joints.RigidJoint` | Hinge |
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+---------------------------------------+---------------------------------------------------------------------+--------------------+
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| :class:`~joints.RigidJoint` | :class:`~joints.RigidJoint` | Fixed |
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+---------------------------------------+---------------------------------------------------------------------+--------------------+
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Objects may have many joints bound to them each with an identifying label. All :class:`~topology.Joint`
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objects have a ``symbol`` property that can be displayed to help visualize
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their position and orientation (the `ocp-vscode <https://github.com/bernhard-42/vscode-ocp-cad-viewer>`_ viewer
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has built-in support for displaying joints).
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.. note::
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If joints are created within the scope of a :class:`~build_part.BuildPart` builder, the ``to_part``
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parameter need not be specified as the builder will, on exit, automatically transfer the joints created in its
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scope to the part created.
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The following sections provide more detail on the available joints and describes how they are used.
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.. py:module:: joints
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***********
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Rigid Joint
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***********
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A rigid joint positions two components relative to each another with no freedom of movement. When a
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:class:`~joints.RigidJoint` is instantiated it's assigned a ``label``, a part to bind to (``to_part``),
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and a ``joint_location`` which defines both the position and orientation of the joint (see
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:class:`~geometry.Location`) - as follows:
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.. code-block:: build123d
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RigidJoint(label="outlet", to_part=pipe, joint_location=path.location_at(1))
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Once a joint is bound to a part this way, the :meth:`~topology.Joint.connect_to` method can be used to
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repositioning another part relative to ``self`` which stay fixed - as follows:
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.. code-block:: build123d
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pipe.joints["outlet"].connect_to(flange_outlet.joints["pipe"])
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.. note::
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Within a part all of the joint labels must be unique.
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The :meth:`~topology.Joint.connect_to` method only does a one time re-position of a part and does not
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bind them in any way; however, putting them into an :ref:`assembly` will maintain there relative locations
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as will combining parts with boolean operations or within a :class:`~build_part.BuildPart` context.
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As a example of creating parts with joints and connecting them together, consider the following code where
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flanges are attached to the ends of a curved pipe:
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.. image:: assets/rigid_joints_pipe.png
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.. literalinclude:: rigid_joints_pipe.py
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:language: build123d
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:emphasize-lines: 19-20, 23-24
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Note how the locations of the joints are determined by the :meth:`~topology.Mixin1D.location_at` method
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and how the ``-`` negate operator is used to reverse the direction of the location without changing its
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position. Also note that the ``WeldNeckFlange`` class predefines two joints, one at the pipe end and
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one at the face end - both of which are shown in the above image (generated by ocp-vscode with the
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``render_joints=True`` flag set in the ``show`` function).
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.. autoclass:: RigidJoint
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..
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:exclude-members: connect_to
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.. method:: connect_to(other: BallJoint, *, angles: RotationLike = None)
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.. method:: connect_to(other: CylindricalJoint, *, position: float = None, angle: float = None)
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:noindex:
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.. method:: connect_to(other: LinearJoint, *, position: float = None)
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:noindex:
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.. method:: connect_to(other: RevoluteJoint, *, angle: float = None)
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:noindex:
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.. method:: connect_to(other: RigidJoint)
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:noindex:
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Connect the ``RigidJoint`` to another Joint.
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..
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**************
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Revolute Joint
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**************
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Component rotates around axis like a hinge. The :ref:`joint_tutorial` covers Revolute Joints in detail.
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During instantiation of a :class:`~joints.RevoluteJoint` there are three parameters not present with
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Rigid Joints: ``axis``, ``angle_reference``, and ``range`` that allow the circular motion to be fully
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defined.
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When :meth:`~topology.Joint.connect_to` with a Revolute Joint, an extra ``angle`` parameter is present
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which allows one to change the relative position of joined parts by changing a single value.
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.. autoclass:: RevoluteJoint
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..
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:exclude-members: connect_to
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.. method:: connect_to(other: RigidJoint, *, angle: float = None)
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Connect the ``RevoluteJoint`` to a ``RigidJoint``
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************
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Linear Joint
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************
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Component moves along a single axis as with a sliding latch shown here:
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.. image:: assets/joint-latch-slide.png
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The code to generate these components follows:
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.. literalinclude:: slide_latch.py
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:language: build123d
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:emphasize-lines: 30, 52, 55
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.. image:: assets/joint-latch.png
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:width: 65 %
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.. image:: assets/joint-slide.png
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:width: 27.5 %
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Note how the slide is constructed in a different orientation than the direction of motion. The
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three highlighted lines of code show how the joints are created and connected together:
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* The :class:`~joints.LinearJoint` has an axis and limits of movement
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* The :class:`~joints.RigidJoint` has a single location, orientated such that the knob will ultimately be "up"
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* The ``connect_to`` specifies a position that must be within the predefined limits.
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The slider can be moved back and forth by just changing the ``position`` value. Values outside
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of the limits will raise an exception.
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.. autoclass:: LinearJoint
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..
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:exclude-members: connect_to
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.. method:: connect_to(other: RevoluteJoint, *, position: float = None, angle: float = None)
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.. method:: connect_to(other: RigidJoint, *, position: float = None)
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:noindex:
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Connect the ``LinearJoint`` to either a ``RevoluteJoint`` or ``RigidJoint``
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*****************
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Cylindrical Joint
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*****************
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A :class:`~joints.CylindricalJoint` allows a component to rotate around and moves along a single axis
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like a screw combining the functionality of a :class:`~joints.LinearJoint` and a
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:class:`~joints.RevoluteJoint` joint. The ``connect_to`` for these joints have both ``position`` and
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``angle`` parameters as shown below extracted from the joint tutorial.
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.. code-block::python
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hinge_outer.joints["hole2"].connect_to(m6_joint, position=5 * MM, angle=30)
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.. autoclass:: CylindricalJoint
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..
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:exclude-members: connect_to
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.. method:: connect_to(other: RigidJoint, *, position: float = None, angle: float = None)
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Connect the ``CylindricalJoint`` to a ``RigidJoint``
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**********
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Ball Joint
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**********
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A component rotates around all 3 axes using a gimbal system (3 nested rotations). A :class:`~joints.BallJoint`
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is found within a rod end as shown here:
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.. image:: assets/rod_end.png
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.. literalinclude:: rod_end.py
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:language: build123d
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:emphasize-lines: 40-44,51,53
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Note how limits are defined during the instantiation of the ball joint when ensures that the pin or bolt
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within the rod end does not interfere with the rod end itself. The ``connect_to`` sets the three angles
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(only two are significant in this example).
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.. autoclass:: BallJoint
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..
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:exclude-members: connect_to
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.. method:: connect_to(other: RigidJoint, *, angles: RotationLike = None)
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Connect a ``BallJoint`` to a ``RigidJoint``
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