Rotational Detent

Double-sided, spring-loaded rotational detent

Library

Brakes & Detents/Rotational

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 detent width, or with a lookup table. The model also includes viscous damping and kinetic friction between the rod and case. You can set the friction to zero.

Ports

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

Dialog Box and Parameters

Detent Characteristics

Parameterization

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

  • By peak torque and detent width — Specify detent characteristics by the peak torque and the detent width.

     Peak Torque and Detent Width

  • By lookup table — 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.

     Lookup Table

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

  • By angle vector — Specify detent spacing by custom intervals. If you select this option, the panel changes from its default option.

     Custom intervals

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 Model

As the rod rotates over the case, the relative rotation ϕ = ϕRϕC causes a torque τ to develop. Depending on your choice of parameterization, the torque model is defined by the peak torque and detent width, or by a lookup table 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 Detent Width

If you choose the peak torque and detent 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.

Lookup Table

With the lookup table 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-detent width or the lookup table parameterization, the kinetic friction is independent of the detent normal force.

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