Description of different joints in the DMU Kinematics Workbench of CATIA V5-6
Kinematics is the motion of objects without regarding forces.
Kinetics is forces that cause motion and acceleration which is the result of the motion.
Planar Joints have 3 degrees of freedom which are translation in the x-direction and y-direction and rotation about the z-axis. Example is a block sliding on a flat plane.
Prismatic Joints have 1 degree of freedom which is translation in an axis direction. Example is if a block was sliding along a flat plane but with the edges coincident allowing no rotation.
Cylindrical Joints have 2 degrees of freedom which are an angle of rotation and a translation along a direction. Example is a the axis of a pole translating along the axis of a hole.
Spherical Joints have 3 degrees of freedom which only allow for rotations. There are no translation capabilities. Example of a spherical joint would be a ball joint.
Revolute Joints have 1 rotational degree of freedom. Two lines and two planes are required. The plane can be offset from the other plane but must be normal to the axis.
Gear Joints are made up of two revolute joints and allow for a gear ration and direction of rotation. They have 1 degree of freedom and do not need actual teeth for simulation.
Rigid Joints have no degrees of freedom and simulates a part being fixed. The parts are locked together and do not have to be in contact.
Rack Joints are a gear joint were the radius of curvature of the gears is infinite. They are made using a revolute and a prismatic joint. The direction of rotation can be specified and it has one 1 degree of freedom which can be either translation or rotation.
Universal Joint consists of two shafts constrained in its axis with a revolute or cylindrical joint. The angle of the shaft will be driven by the angle of the other shaft.
Screw Joints are either translated along an axis or rotated about an axis. The pitch of the screw needs to be specified along with the axis.
Point Surface Joints have 3 degrees of rotation and 2 translation degrees of freedom. The point has be actually on the surface before the joint is applied.
Point Curve Joint has 3 degrees of rotation and 1 translation degree of freedom along a curve. The point needs to be actually on the curve before the point is applied.
Slide Curve Joint consists of 2 curves that remake in contact but allows one curve to slide along the other curve. The curves must be coincident and tangent at a given point before the joint is applied.
Roll Curve Joint allows two curves to stay in contact. The curves must be coincident and tangent at a given point before the joint is applied.
Cable Joints can be used to simulate a cable and pulley. They can be thought of as two prismatic with a pulley in between. There is no friction required for this joint.
Other Tools that are often used:
The Assembly Constraints Conversation Tool will automatically make joints that CATIA sees are needed based on the constraints. This is very handy once you understand the kind of constraints that each joint will make and you can make them before going into kinematics. If you constrain the product properly in the assembly then the tool should make all the joints for you. This tool is also helpful if for finding what other joints are still needed if you are doing a complex simulation and still have many degrees of freedom left. TIP: Do all the basic/obvious joints first, pay attention to how your constraining it and this tool will do most of your work for you.
The Speed and Acceleration Tool is for adding a sensor to a specific point on a part with a reference to another part (usually the part that is fixed). This allows you to track the acceleration, velocity, and displacement on a specific point of the simulation.
Mechanism Analysis is a tool that will show you the data of your mechanism. You can visually see joints which is useful for complex assemblies. You can also see the joints you created are valid and having an effect on the degrees of freedom.
Other Tools that are often used:
The Assembly Constraints Conversation Tool will automatically make joints that CATIA sees are needed based on the constraints. This is very handy once you understand the kind of constraints that each joint will make and you can make them before going into kinematics. If you constrain the product properly in the assembly then the tool should make all the joints for you. This tool is also helpful if for finding what other joints are still needed if you are doing a complex simulation and still have many degrees of freedom left. TIP: Do all the basic/obvious joints first, pay attention to how your constraining it and this tool will do most of your work for you.
The Speed and Acceleration Tool is for adding a sensor to a specific point on a part with a reference to another part (usually the part that is fixed). This allows you to track the acceleration, velocity, and displacement on a specific point of the simulation.
Mechanism Analysis is a tool that will show you the data of your mechanism. You can visually see joints which is useful for complex assemblies. You can also see the joints you created are valid and having an effect on the degrees of freedom.
Very useful! Thanku so much!
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