Ideal Rotational Motion Sensor

Motion sensor in mechanical rotational systems

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Libraries:
Simscape / Foundation Library / Mechanical / Mechanical Sensors

Description

The Ideal Rotational Motion Sensor block represents an ideal mechanical rotational motion sensor, that is, a device that converts an across variable measured between two mechanical rotational nodes into a control signal proportional to acceleration, angular velocity, or position (angle). You can specify the initial angular position (offset) as a block parameter.

The sensor is ideal since it does not account for inertia, friction, delays, energy consumption, and so on.

Connections R and C are mechanical rotational conserving ports that connect the block to the nodes where motion is being monitored. The block positive direction is from port R to port C. This means that the velocity is measured as ω = ω_R – ω_C, where ω_R, ω_C are the absolute angular velocities at ports R and C, respectively. The Measurement reference parameter lets you disable port C and measure with respect to ground.

Connections α, W, and A are physical signal output ports for angular acceleration, velocity, and displacement, respectively. The visibility of these ports is controlled by block parameters. If you enable port α, the block performs additional computations, to measure acceleration based on velocity. To avoid unnecessary model complexity, it is recommended that in each instance of the block you enable only the ports that you actually use for measurement.

The Wrap angle to [0, 2*pi] check box lets you control the angular displacement output range. When selected, it keeps angular displacement within the range from 0 to 2π radians (360 degrees), regardless of the number of revolutions performed by the object and the direction of rotation. When this check box is cleared, the output range is unrestricted.

The figure demonstrates the difference between the two options.

In this example, the object is moving at 6 rad/s in the positive direction for the first 5 seconds, and then switches to the negative direction at the same speed. The default angular displacement output (line 1) shows that the object turned forward by 30 rad and then turned back in the negative direction, continuing until –20 rad. If you select the Wrap angle to [0, 2*pi] check box, the output (line 2) stays in the range from 0 to 2π rad.

Selecting the Wrap angle to [0, 2*pi] check box simplifies development of models with complex relationship between model parameters and rotation angle, such as pumps and motors.

Examples

Permanent Magnet DC Motor

This model is based on a Faulhaber Series 0615 DC-Micromotor. The parameters values are set to match the 1.5V variant of this motor. The model uses these parameters to verify manufacturer-quoted no-load speed, no-load current, and stall torque.

• Open Model

Mechanical Rotational System with Stick-Slip Motion

A mechanical rotational system with stick-slip friction. An inertia is connected to a fixed point by spring and damper. The inertia is driven by a velocity source via a stick-slip friction element. The friction element has a difference between the breakaway and the Coulomb frictions, resulting in stick-slip motion of the inertia.

• Open Model

Ports

Output

α — Acceleration, rad/s^2

physical signal

Physical signal output port for angular acceleration.

Dependencies

To enable this port, select the Acceleration check box.

W — Angular velocity, rad/s

physical signal

Physical signal output port for angular velocity.

Dependencies

To enable this port, select the Velocity check box.

A — Position (angular displacement), rad

physical signal

Physical signal output port for angular displacement.

Dependencies

To enable this port, select the Position check box.

Conserving

R — Rod (positive probe)

mechanical rotational

Mechanical rotational conserving port associated with the sensor positive probe.

C — Case (reference probe)

mechanical rotational

Mechanical rotational conserving port associated with the sensor negative (reference) probe.

Dependencies

To enable this port, set the Measurement reference parameter to Difference.

Parameters

Measurement reference — Select whether to perform absolute or relative measurements

Difference (default) | Absolute

Select whether to perform absolute or relative measurements:

• Difference — Measure the acceleration, velocity, and position of port R relative to port C.

• Absolute — Disable port C and measure the acceleration, velocity, and position of port R with respect to ground (internal reference node).

Acceleration — Control output port visibility to measure angular acceleration

off (default) | on

Selecting this check box exposes output port α, which lets you measure angular acceleration. Exposing port α also involves additional computations, to measure acceleration based on velocity, therefore this port is off by default.

Velocity — Control output port visibility to measure angular velocity

on (default) | off

Selecting this check box exposes output port W, which lets you measure angular velocity.

Position — Control output port visibility to measure angular displacement

on (default) | off

Selecting this check box exposes output port A, which lets you measure position (angular displacement).

Wrap angle to [0, 2*pi] — Control output range for angular displacement

off (default) | on

When set to On, keeps angular displacement output by the sensor within the range from 0 to 2π radians (360 degrees), regardless of the number of revolutions performed by the object and the direction of rotation. When set to Off, the output range is unrestricted.

Selecting this check box simplifies development of models with complex relationship between model parameters and rotation angle, such as pumps and motors.

Dependencies

To enable this parameter, select the Position check box.

Initial angle — Sensor initial offset

0 rad (default)

Sensor initial angular position (offset).

Dependencies

To enable this parameter, select the Position check box.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2007a

R2022b: Measure acceleration, measure with respect to ground, and parametrically control visibility of output ports

The block enhancements include:

• An additional physical signal output port, α, that lets you measure angular acceleration.

• Additional parameters (Acceleration, Velocity, and Position) that control the visibility of physical signal output ports, letting you expose only the ports that are actually used for measurement in each particular instance. This enhancement helps improve the block diagram readability. Also, because exposing the acceleration measurement port involves additional computations, this port is hidden by default and it is recommended that you do not expose it unless you need to measure acceleration.

• In previous releases, the blocks measured only relative velocity and position of port R with respect to port C. Now, the new Measurement reference parameter lets you disable port C and measure with respect to ground (internal reference node).

These enhancements have no compatibility impact on models created in previous releases.