Rotational Detent

Description

The Rotational Detent block represents a double-sided, spring-loaded rotational detent.

The detent rod rotates over the detent case. The case has notches or magnets that create a net relative torque with the rod as the rod rotates. With the block, you can model rotational detents with peak torque and notch width, or with a table lookup. The model also includes viscous damping and kinetic friction between the rod and case. You can set the friction to zero.

Rotational Detent Model

As the rod rotates over the case, the relative rotation ϕ = ϕ_R – ϕ_C causes a torque τ to develop. Depending on your choice of parameterization, the torque model is defined by the peak torque and notch width, or by a table lookup specifying relative rotation versus torque.

Regardless of the parameterization, if you specify multiple detents, all detents have the same torque-relative rotation function.

Peak Torque and Notch Width

If you choose the peak torque and notch width parameterization, the block ensures that the torque-relative rotation curve provides a continuous torque and torque derivative over the detent region. The peak torques are halfway between the detent center and detent edge, as shown in the following figure.

By Table Lookup

With the table lookup parameterization, you can create an arbitrary function relating torque to relative rotation. If you create such a function, consider the following best practices.

Energy Conservation

If you want to ensure that the detent conserves energy, the total integral of the torque-relative rotation curve (area under the curve) must be zero.

Simulation Performance

To stabilize simulation of the detent, avoid discontinuities in the torque-relative rotation function.

Limitations

The model does not account for inertia. Add inertia terms externally to the R and C ports as required.
If you use the peak torque-notch width or the table lookup parameterization, the kinetic friction is independent of the detent normal force.

Ports

R and C are rotational conserving ports associated with the rod and case, respectively.

Parameters

Detent Characteristics

Parameterization

Select how to specify the detent characteristics. The default is By peak torque and notch width.

By peak torque and notch width — Specify detent characteristics by the peak torque and the notch width.
Peak Torque and Notch Width
Peak torque
The peak torque developed inside the detent. The default is 0.25.
From the drop-down list, choose units. The default is newton-meters (N*m).
Notch width
The width of the region where the torque develops. The default is 5.
From the drop-down list, choose units. The default is degrees (deg).
By table lookup — Define the detent characteristics by one-dimensional table lookup based on the relative displacement between the slider and case. If you select this option, the panel changes from its default option.
Table Lookup
Relative rotation vector
Specify the vector of input relative rotations that correspond to the values in Torque vector. These two vectors must be of the same size. The angles must be specified in strictly increasing order. The default values are [-5.0 -4.0 -3.0 -1.0 1.0 3.0 4.0 5.0].
From the drop-down list, choose units. The default is degrees (deg).
Torque vector
Specify the vector of input values for the developed torque that correspond to the values in Relative rotation vector. The default values are [0 0 -0.25 -0.10 0.10 0.25 0 0].
From the drop-down list, choose units. The default is newton-meters (N*m).
Initial relative rotation
The relative angle of the rod and case when simulation starts. The default is 0.
From the drop-down list, choose units. The default is degrees (deg).
Interpolation method
Select one of these interpolation methods for approximating the output value when the input value is between two consecutive grid points:
Linear — Select this, default, option to get the best performance.
Smooth — Select this option to produce a continuous curve with continuous first-order derivatives.
For more information on interpolation algorithms, see the PS Lookup Table (1D) block reference page.

Spacing

Detent spacing

Select how to specify the detent spacing. The default is Regularly spaced.

Regularly spaced — Specify detent spacing by regular intervals.
Regular spacing
Number of detents
Specify the number of identical, regularly spaced detents. Must be greater than or equal to 1. The default is 1.
Creates a number of detents evenly spaced from –180 to +180 degrees, with one detent center at 0 degrees. Non-integer values are rounded to the nearest integer.
By angle vector — Specify detent spacing by custom intervals. If you select this option, the panel changes from its default option.
Custom intervals
Vector of detent centers
Specify the locations of the centers of identical detents as a vector of angles. These values must lie between –180 and +180 degrees. The minimum spacing between the detents must be greater than the Notch width parameter. The default values are [-40 0 30 85].
From the drop-down list, choose units. The default is degrees (deg).

Friction

Viscous friction coefficient

Specify the viscous friction coefficient for the rod-case contact. Must be greater than or equal to 0. The default is 0.1.

From the drop-down list, choose units. The default is newton-meters/(radians/second) (N*m/(rad/s)).

Friction to peak torque ratio

Specify the kinetic friction coefficient for the rod-case contact. Must be greater than or equal to 0. The default is 0.01.

The kinetic friction is this ratio multiplied by the peak torque.

Friction velocity threshold

Specify the relative angular velocity required for peak kinetic friction in the detent. Must be greater than 0. The default is 10.

From the drop-down list, choose units. The default is revolutions/minute (rpm).

Rotational Detent

Library

Description