I would like to build a mechanical module that acts like a spring with electronically controllable stiffness (spring rate).

For instance, let's imagine a solid, metallic cube, 0.5 m each side. On the top side of the cube, there is a chair sitting on top of a solid mechanical spring. When you sit on the chair, it would go down proportionally to your weight, and inversely proportional to the spring's rate.

What I want is that this spring's rate be electronically adjustable in real time, for instance a microcontroller system might increase the spring's rate when it detects a larger weight.

I'm using this example to best describe what I want to achieve because I'm not a robotics specialist and I don't know the inside terms.

Is there already an electro-mechanic module as the one I'm describing? (obviously nevermind the cube and the chair, it's the spring I'm interested in).

  • $\begingroup$ Electronic suspension kits are available -- they change damper characteristics rather than spring characteristics, in real time. $\endgroup$ – James Waldby - jwpat7 Jun 13 '15 at 18:41
  • $\begingroup$ @JamesWaldby-jwpat7 most of those do the opposite, they replace the "expensive electronic shocks" with a normal system instead, i.e. a downgrade $\endgroup$ – user2813274 Apr 1 at 18:01

Like jwpat said, I think the only package you'll find for what you're looking for is active suspension, but good luck getting official support from the manufacturer unless you have some automotive OEM sponsorship.

Note that jwpat linked to adaptive suspension parts, which vary damping as mentioned, not active suspension, which uses an actuator to do things more similar to what you are looking for.

For guidelines on building your own, I would look at available literature on series elastic actuators, which are essentially linear actuators that drive springs.

Essentially, you use the (linear fixed) spring constant and a desired force to estimate what the spring compression should be (this would be your input), then you use position feedback on the spring to get actual spring compression. Use PID control or whatever else you like to drive the spring compression to yield the desired force.

Note that you get to pick the force, so if you want the spring to be nonlinear or of varying constants you can just choose what you want.

All of this assumes what you have asked for is the best solution to your problem. What effect are you going for that you need variable spring constants? Are you looking for a constant force output or some kind of constant displacement? Are you looking for a nonlinear spring or user-selectable springs? More information on your problem will let us give you better help.

Hydraulics can also give you what you're looking for, but, even though you asked for electro-mechanical, hydraulics are usually out of the scope of most people's projects.


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