Mechanism Design and Mechanism Dynamics > Mechanism Dynamics > Measures > About Connection Reaction Measures
About Connection Reaction Measures
A reaction measure evaluates the load generated at a connection in response to external forces. You can use a joint reaction measure, for example, to verify that you are within the load rating for a bearing.
Use the Measure Definition dialog box to define a connection reaction measure. You can set the coordinate system to use as the measure’s frame of reference and you can also specify which body to measure for the exerted reaction force.
However, the default coordinate system of the selected connection may not correspond to the WCS or the LCS of any of the bodies. Select the Select coordinate system checkbox to choose a specific coordinate system.
When you have selected a connection and a component of force or moment to measure, a shaded, colored arrow appears on the selected connection, indicating the direction that is actually used in the calculation. No arrow appears if you select a component that gives the magnitude of the force or moment. Consider carefully whether this direction is actually the one that you want for the force or moment.
You can create reaction measures for these types of connections:
Connection sets—Evaluate the reaction force or the moment exerted by the joint on either of its bodies. The force or moment component that you can measure depends upon the type of connection set. A component along a motion axis may include the reaction as a result of motion axis limit or as a result of friction along that axis.
* To measure the sum of applied forces on a connection, such as motors and springs, use a net load measure.
Cam-follower connections—Evaluate the force at the contact point between the two cams in a cam-follower connection.
* The reaction measure for a cam-follower connection does not include the calculation of impact forces. You can measure reaction forces on a cam-follower connection with liftoff while the cams are in contact, but reaction force values will be zero if the cams separate. If your cams liftoff and contact several times during an analysis, that is, the cams bounce, use an impact or impulse measure to monitor the contact events.
You can measure the following components for cam-follower connections:
Normal force—The reaction force perpendicular to the cam-follower connection at the point of contact. In a given frame of reference, a positive reaction force works to push the two cams in the connection together, and a negative force works to pull them apart.
Tangential force–The reaction force tangential to the cam-follower connection at the point of contact. A tangential force acts to slide the cams past each other.
Slip–Checks whether a cam-follower connection has slipped during a force balance analysis. If a slip has occurred, the measure returns a value of 1. If not, it returns a value of 0.
Slot-follower connections—Evaluate the force exerted by the slot on either of its bodies. More force is exerted when a follower reaches one of the endpoints of the slot or there is friction on the slot axis.
Gear pairs—Evaluate the reaction force or torque exerted on one of the bodies in a gear pair. For a gear with a rotational motion axis, you can measure the torque exerted on that axis. For a gear with a translational motion axis, such as the rack in a rack and pinion gear pair, you can measure the linear force exerted on that axis. You can also use dynamic gears to measure the various forces that affect the pitch point and moments acting at centers of pitch circles.
Belts—Evaluate the torque exerted by the belt on any of its pulley axes. A list of pulleys is available for a selected belt.
3D contacts—Evaluate the force at a contact point of a 3D contact. The components and their meaning are similar to the cam-follower connections. The main difference is that the 3D contact impact occurs over a period of time, while the cam impact is momentary. For this reason, the 3D force calculation contact includes impact.