SimMechanics

Parallel Constraint

Constrain the body axis vectors of two bodies to be parallel

Library

Constraints & Drivers

Description

The two Bodies connected by a Parallel Constraint are restricted in their relative rotational motion. The Parallel Constraint is connected on either side to a Body CS, one on each Body. A vector a_B defined in one Body CS on the base body remains parallel to a second vector a_F defined in another Body CS on the follower body.

The Parallel Constraint block requires that:

|a_Ba_F|/(|a_B||a_F|) = 1.

You specify the initial direction to which both vectors must remain parallel.

Constraints restrict relative degrees of freedom (DoFs) between a pair of bodies. Locally in a machine, they replace a Joint as the expression of the DoFs. Globally, Constraint blocks must occur topologically in closed loops. Like Bodies connected to a Joint, the two Bodies connected to a Constraint are ordered as base and follower, fixing the direction of relative motion.

Parallel Constraint is assembled: the Body CS origin on the base body must be initially collocated with the Body CS origin on the follower body, to within assembly tolerance.

You can connect a Constraint block to a Constraint & Driver Sensor, but not to an Actuator. The Constraint & Driver Sensor measures the reaction forces/torques between the constrained bodies.

Dialog Box and Parameters

The dialog box has two active areas, Connection parameters and Parameters.

Connection Parameters

Current base

When you connect the base (B) Connector Port on the Parallel Constraint block to a Body CS Port on a Body, this parameter is automatically reset to the name of this Body CS. See the following Parallel Constraint base and follower Body Connector Ports figure.

Current follower

When you connect the follower (F) Connector Port on the Parallel Constraint block to a Body CS Port on a Body, this parameter is automatically reset to the name of this Body CS. See the following Parallel Constraint base and follower Body Connector Ports figure.

Number of sensor ports

Using this spinner menu, you can set the number of extra Connector Ports needed for connecting Constraint & Driver Sensor blocks to this Constraint. The default is 0.

The base (B)-follower (F) Body sequence determines the sense of positive motion. Positive rotation is the follower rotating in the right-handed sense about the rotation axis.

Parallel Constraint base and follower Body Connector Ports

Parameters

Parallel constraint axis [x y z]

Enter the axis vector defining the initial direction of the two body axis vectors a_b, a_f. These body axis vectors are restricted to always remain parallel to this initial axis. The default is [1 0 0].

Reference csys

Using the pull-down menu, choose the coordinate system (World, the base Body CS, or the follower Body CS) whose coordinate axes the initial Parallel constraint axis is oriented with respect to. This CS also determines the absolute meaning of reaction forces/torques at this Constraint. The default is WORLD.

See Also

Angle Driver, Constraint & Driver Sensor, Velocity Driver

See Modeling Constraints and Drivers for more on restricting DoFs with Constraints.

See Checking Schematic Topology and How SimMechanics Works for more on using constraints in closed loops.

See Creating Constraints and Drivers.

Linear Driver

Planar