Joint with two prismatic primitives
This block represents a joint with two translational degrees of freedom. Two prismatic primitives provide the two translational degrees of freedom. Base and follower frames share the same orientation for all time. During simulation, translation occurs about two of the common frame axes, in the order X, Y.
A set of ptional state targets guide assembly for each joint primitive. Targets include position and velocity at time zero. A priority level sets the relative importance of the state targets. If two targets are incompatible, the priority level determines which of the targets to meet. In models with motion-actuated joints, the motion input signal takes precedence over the joint state targets, dictating the model configuration at simulation time zero.
Internal mechanics account for energy storage and dissipation in each joint primitive. Joint springs act as energy storage elements. Joint dampers act as energy dissipation elements. Springs and dampers are strictly linear.
Each joint primitive has a set of optional actuation and sensing ports. Actuation ports accept physical signal inputs that drive the joint primitives. These inputs can be forces and torques or a desired joint trajectory. Sensing ports provide physical signal outputs that measure joint primitive motion as well as actuation forces and torques. Actuation modes and sensing types vary with joint primitive.
Expandable sections provide parameters and options for the different joint primitives. These primitives are the basic elements of a joint block. They can be of three types: Revolute, Prismatic, or Spherical. Joint blocks can have all, some, or none of these joint primitives. For example, the Weld joint block has none.
The expandable sections are hierarchical. The top level of an expandable section identifies joint primitive type and axis, e.g., X Prismatic Primitive (Px). Within a joint primitive section are four parameter groups. These contain parameters and options for a joint primitive's initial state, internal mechanics, actuation, and sensing.
Specify the prismatic primitive state targets and their priority levels. A state target is the desired value for one of the joint state parameters—position and velocity. The priority level is the relative importance of a state target. It determines how precisely the target must be met. Use the Model Report tool in Mechanics Explorer to check the assembly status for each joint state target.
Select this option to specify the desired joint primitive position at time zero. This is the relative position, measured along the joint primitive axis, of the follower frame origin with respect to the base frame origin. The specified target is resolved in the base frame. Selecting this option exposes priority and value fields.
Select this option to specify the desired joint primitive velocity at time zero. This is the relative velocity, measured along the joint primitive axis, of the follower frame origin with respect to the base frame origin. It is resolved in the base frame. Selecting this option exposes priority and value fields.
Select state target priority. This is the importance level assigned to the state target. If all state targets cannot be simultaneously satisfied, the priority level determines which targets to satisfy first and how closely to satisfy them. This option applies to both position and velocity state targets.
|High (desired)||Satisfy state target precisely|
|Low (approximate)||Satisfy state target approximately|
Specify the prismatic primitive internal mechanics. Internal mechanics include linear spring forces, accounting for energy storage, and damping forces, accounting for energy dissipation. You can ignore internal mechanics by keeping spring stiffness and damping coefficient values at 0.
Enter the spring equilibrium position. This is the distance between base and follower frame origins at which the spring force is zero. The default value is 0. Select or enter a physical unit. The default is m.
Enter the linear spring constant. This is the force required to displace the joint primitive by a unit distance. The default is 0. Select or enter a physical unit. The default is N/m.
Enter the linear damping coefficient. This is the force required to maintain a constant joint primitive velocity between base and follower frames. The default is 0. Select or enter a physical unit. The default is N/(m/s).
Specify actuation options for the prismatic joint primitive. Actuation modes include Force and Motion. Selecting Provided by Input from the drop-down list for an actuation mode adds the corresponding physical signal port to the block. Use this port to specify the input signal. Actuation signals are resolved in the base frame.
Select an actuation force setting. The default setting is None.
|Actuation Force Setting||Description|
|None||No actuation force.|
|Provided by Input||Actuation force from physical signal input. The signal provides the force acting on the follower frame with respect to the base frame along the joint primitive axis. An equal and opposite force acts on the base frame.|
|Automatically computed||Actuation force from automatic calculation. SimMechanics™ computes and applies the actuation force based on model dynamics.|
Select an actuation motion setting. The default setting is Automatically Computed.
|Actuation Motion Setting||Description|
|Provided by Input||Joint primitive motion from physical signal input. The signal provides the desired trajectory of the follower frame with respect to the base frame along the joint primitive axis.|
|Automatically computed||Joint primitive motion from automatic calculation. SimMechanics computes and applies the joint primitive motion based on model dynamics.|
Select the variables to sense in the prismatic joint primitive. Selecting a variable exposes a physical signal port that outputs the measured quantity as a function of time. Each quantity is measured for the follower frame with respect to the base frame. It is resolved in the base frame. You can use the measurement signals for analysis or as input in a control system.
Select this option to sense the relative position of the follower frame origin with respect to the base frame origin along the joint primitive axis.
Select this option to sense the relative velocity of the follower frame origin with respect to the base frame origin along the joint primitive axis.
Select this option to sense the relative acceleration of the follower frame origin with respect to the base frame origin along the joint primitive axis.
Select this option to sense the actuation force acting on the follower frame with respect to the base frame along the joint primitive axis.
The block contains frame ports B and F, representing base and follower frames, respectively. Selecting actuation or sensing options from the dialog box exposes additional physical signal ports. Use the ports to input an actuation signal or to output the chosen sensing parameter.
A unique label identifies the actuation or sensing component associated with a port. This label can contain one or two letters. The first letter identifies the actuation or sensing parameter, applied to or measured from the follower frame. The second letter identifies the axis for that parameter, resolved in the base frame. This letter can be x, y, or z.
The table describes the first letters in the port labels for this block.