SimMechanics

Screw

Represent a composite joint with one translational DoF and one rotational DoF, with parallel translation and rotation axes and a linear pitch constraint between translational and rotational motion

Library

Joints

Description

The Screw block represents a composite joint with one translational degree of freedom (DoF) as one prismatic primitive and one rotational DoF as one revolute primitive. The translation and rotation axes are parallel. The translational and rotational DoFs are constrained by a pitch constraint to have proportional motion.

You must connect each side of the Joint block to a Body block at a Body coordinate system (CS) point. The Screw block is assembled: the origins of these Body CSs must lie along the primitive axes, and the Body CS origins on either side of the Joint must be spatially collocated points, to within assembly tolerances.

You can connect any Joint block to two and only two Body blocks, and Joints have a default of two Connector Ports for connecting to base and follower Bodies.

A Joint block represents only the abstract relative motion of two bodies, not the bodies themselves. You must specify a reference CS to define the direction of the joint axis.

Dialog Box and Parameters

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

Connection Parameters

Current base

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

The base Body is automatically connected to the joint primitive R1 in the primitive list in Parameters.

Current follower

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

The follower Body is automatically connected to the joint primitive R1 in the primitive list in Parameters.

Number of sensor/actuator ports

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

The motion of revolute primitives is specified in angular units.

The base (B)-follower (F) Body sequence determines the sense of positive motion. Positive rotation is the follower moving around the rotational axis following the right-hand rule.

Screw base and follower Body Connector Ports

Parameters

Toggle between the Axes and Advanced panels with the tabs.

The entries on the Axes pane are required. Each DoF primitive in Screw has an entry line. These lines specify the direction of the axes of action of the DoFs that the Screw represents.

Name - Primitive

The primitive list states the name and type of the joint primitive that makes up the Screw block: revolute primitive R1.

Axis of action [x y z]

Enter here as a three-component vector the directional axes defining the allowed motions of this primitive and its corresponding DoF:

• Revolute: axis of rotation
  The default vectors are shown in the dialog box above. The axis is a directed vector whose overall sign matters.

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 vector axis of action is oriented with respect to. This CS also determines the absolute meaning of forces/torques and motion along/about the joint axis. The default is WORLD.

The Advanced pane is optional. You use it to control the way SimMechanics interprets the topology of your schematic diagram.

Mark as the preferred cut joint

In a closed loop, one and only one joint is cut during the simulation. SimMechanics does the cutting internally and automatically.

If you want this particular joint to be weighted preferentially for cutting during the simulation, select the check box. The default is unselected.

Pitch Parameters

The Pitch parameters control how far the screw translates for each revolution.

Pitch

Linear distance the screw travels along the screw axis for each complete revolution (turn) of 2 radians (360^o). The default is 1.

Units (per revolution)

In the pull-down menu, choose the units for the pitch linear distance. The default is mm (millimeters).

See Also

Cylindrical, Prismatic, Revolute

See Modeling Joints for more on representing DoFs with Joints.

See Checking Schematic Topology and How SimMechanics Works for more on closed loops and cutting.

RotationMatrix2VR

Six-DoF