SimMechanics    
Joint Sensor

Measure the motion and force/torque of a joint primitive

Library

Sensors & Actuators

Description

The Joint Sensor block measures the position, velocity, and/or acceleration of a joint primitive in a Joint block.

The Joint Sensor measures the motion along/about the joint axis (or about the pivot point for a spherical primitive) in the reference coordinate system (CS) specified for that joint primitive in the Joint's dialog box. The Joint connects a base and a follower Body. The base-follower sequence determines the sense of the motion.

Depending on the joint primitive being sensed, you measure one of these motion types:

The input is the Connector Port connected to the Joint being sensed. The outport is a set of Simulink signals or one bundled Simulink signal of the position, velocity, and/or acceleration of the joint primitive.

A Joint Sensor block measures one joint primitive at a time:

Dialog Box and Parameters

The dialog box has one active area, Measurements.

Measurements

Connected to primitive
In the pull-down menu, choose the joint primitive within the Joint that you want to measure with the Joint Sensor. A primitive Joint block has only one joint primitive.
If the Joint Sensor is not connected to a Joint block, this menu shows only Unknown.

Here is a Joint Sensor connected to a Prismatic that connects two Bodies:

You must add an Sensor port (Connector Port) to the Joint block to connect the Joint Sensor to it. The base (B)-follower (F) Body sequence on the two sides of the Joint determines the sense of the Joint Sensor data.

The Measurements pane you see in the Joint Sensor dialog depends on the type of joint primitive to which you connect the Joint Sensor.

Prismatic joint primitive (P)

Select the check box(es) for each of the possible measurements you want to make: Position, Velocity, Acceleration, Computed Force, Reaction Torque, and Reaction Force.
The computed force is that force along the prismatic axis which reproduces the follower motion with respect to base.
The reaction force and/or torque is (are) 3-component vector(s) of the force and/or torque that the joint primitive transfers to the base or follower Body.
In the Reactions measured on pull-down menu, choose which Body the reaction force and/or torque vector(s) is (are) measured on, Base or Follower. The default is Base. Also choose With respect to coordinate system for the reaction torque and/or force. The default is Absolute (World).
In the pull-down menus, choose the units for each of the measurements you want. The defaults are m (meters), m/s (meters/second), m/s2 (meters/second2), N (Newtons), and N-m (Newton-meters), respectively, for Position, Velocity, Acceleration, Force, and Torque.

The bundled Simulink output signal for a prismatic primitive has these measurements ordered in a row vector. Unselected components are removed from the vector signal:

Position
 Velocity
 Acceleration
 Computed Force
 Reaction Torque (3-vector)
 Reaction Force (3-vector)

Revolute joint primitive (R)

Select the check box(es) for each of the possible measurements you want to make: Angle, Angular velocity, Angular acceleration, Computed Torque, Reaction Torque, and Reaction Force.
The computed torque is that torque about the revolute axis which reproduces the follower motion with respect to base.
The reaction force and/or torque is (are) 3-component vector(s) of the force and/or torque that the joint primitive transfers to the base or follower Body.
In the Reactions measured on pull-down menu, choose which Body the reaction force and/or torque vector(s) is (are) measured on, Base or Follower. The default is Base. Also choose With respect to coordinate system for the reaction torque and/or force. The default is Absolute (World).
In the pull-down menus, choose the units for each of the measurements you want. The defaults are m (meters), m/s (meters/second), m/s2 (meters/second2), N (Newtons), and N-m (Newton-meters), respectively, for Position, Velocity, Acceleration, Force, and Torque.

The bundled Simulink output signal for a revolute primitive has these measurements ordered in a row vector. Unselected components are removed from the vector signal:

Angle
 Angular Velocity
 Angular Acceleration
 Computed Torque
 Reaction Force (3-vector)
 Reaction Torque (3-vector)

Spherical joint primitive (S)

Select the check box(es) for each of the possible measurements you want to make: Quaternion, Quaternion, derivative, and Quaternion, second derivative, Reaction Torque, and Reaction Force.
The reaction force and/or torque is (are) 3-component vector(s) of the force and/or torque that the joint primitive transfers to the base or follower Body.
In the Reactions measured on pull-down menu, choose which Body the reaction force and/or torque vector(s) is (are) measured on, Base or Follower. The default is Base. Also choose With respect to coordinate system for the reaction torque and/or force. The default is Absolute (World).
The quaternion is dimensionless. The time unit for the derivatives is seconds. Each quaternion measurement is a 4-component row vector.

The bundled Simulink output signal for a spherical primitive has these quaternion measurements ordered into a larger row vector. Unselected components are removed from the vector signal:

Quaternion (4-vector)
 Quaternion, derivative (4-vector)
 Quaternion, second derivative (4-vector)
 Reaction Torque (3-vector)
 Reaction Force (3-vector)

Output selected parameters as one signal
Select this check box to convert all the output signals into a single bundled signal. The default is selected. If you unselect it, the Joint Sensor block will grow as many Simulink outports as there are active signals selected, in the same order top to bottom, in the dialog box.
If the check box is selected, the Simulink signal out has all the active signals ordered into a single row vector. The order and type of the signal components depend on the joint primitive, as listed in the Simulink signal tables above.

See Also

Body Sensor, Constraint & Driver Sensor, Joint Actuator, Joint Initial Condition Actuator, Joint Stiction Actuator, Prismatic, Revolute, Spherical

See Creating Joints.

In Simulink, see the Signal Routing Library and the Sinks Library.


  Joint Initial Condition Actuator Joint Stiction Actuator