Variable Rotational Spring

R2026b

Rotational spring with variable spring stiffness

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Variable Rotational Spring block

To add a block to a model, double-click the canvas and start typing the block name. Then, select the block from the list.

Libraries:
Simscape / Driveline / Couplings & Drives / Springs & Dampers

Description

The Variable Rotational Spring block represents a torsional spring with variable spring stiffness. A physical signal input port provides the value of the variable spring stiffness. The magnitude of the spring torque is equal to the product of the physical signal input and the relative angular displacement between the two rotational conserving ports.

The block finds the spring torque, such that:

$$T=\{\begin{array}{cc}K\cdot \theta & K\ge K_{\min }\\ K_{\min }\cdot \theta & K<K_{\min }\end{array}$$

where:

• T is the torque transmitted through the spring.

• K is the spring stiffness, specified at port K.

• K_min is the minimum allowable spring rate, specified by the Minimum spring rate parameter. The block saturates inputs that are below this value.

• θ is the relative angular displacement measured between the two rotational conserving ports, according to $$\theta ={\theta }_{init}+{\theta }_R-{\theta }_C$$

• θ_init is the initial angular deformation between the two rotational conserving ports.

• θ_R is the absolute angular displacement of port R.

• θ_C is the absolute angular displacement of port C.

The block applies equal and opposite spring torques on the two rotational conserving ports. The sign of the spring torque acting on port R is equal to the sign of the relative angular velocity. A positive relative angular velocity corresponds to a positive damping torque acting on port R, and a negative damping torque of equal magnitude acting on port C.

Variables

To set the priority and initial target values for the block variables prior to simulation, use the Initial Targets section in the block dialog box or Property Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Nominal values provide a way to specify the expected magnitude of a variable in a model. Using system scaling based on nominal values increases the simulation robustness. Nominal values can come from different sources, one of which is the Nominal Values section in the block dialog box or Property Inspector. For more information, see Modify Nominal Values for a Block Variable.

Assumptions and Limitations

The value of the spring rate must be greater than zero.

Ports

Input

K — Spring stiffness, N*m/rad

physical signal

Physical signal input port representing the variable spring stiffness, in N*m/rad.

Programmatic Use

Port: K

Conserving

R — Rod

mechanical rotational

Mechanical rotational conserving port associated with the spring rod.

Programmatic Use

Port: R

C — Case

mechanical rotational

Mechanical rotational conserving port associated with the spring case.

Programmatic Use

Port: C

Parameters

Minimum spring rate — Lower bound on spring rate

0.01 N*m/rad (default) | positive scalar

Minimum value allowed for the spring stiffness. The physical signal input saturates below the specified value. The value must be greater than zero.

Programmatic Use

Parameter: Kmin

Extended Capabilities

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

Version History

Introduced in R2013a