# Linear motion with triangle profile

I am looking for a way to generate a linear motion with a triangle motion profile for my hobby project. The travel distance should be 6cm (so 12 cm for round-trip) with constant speed 1.2 m/s or higher. The solution should be able to oscillate at 10 Hz for minutes at time.

The travel distance basically rules out the use solenoids, and the triangle motion profile requirement rules out basic slider-crank mechanism where the linear motion speed changes over time. I am hoping that this is a trivial problem for proper engineers, but as a hobbyist I am struggling to come up with a work-able solution.

Any suggestion will be appreciated.

Thanks

• By "triangle", do you mean x-vs-t or v-vs-t? Apr 27, 2021 at 12:46
• x-vs-t. I realize that my original question implied v-vs-t. Corrected now. Apr 27, 2021 at 12:53

Probably many possibilities. Here's what comes to my mind:

If the load is light, you could mount it on a timing belt. It could still be on a linear guide, to keep its motion perfectly straight. One end of the timing belt is an idler pulley (probably with a belt tension adjustment feature), and the other end is the motor. Drive the timing belt with any motor that can produce constant speed with the precision you need.

Conventionally, electromechanical / optical / magnetic limit switches would sense the end positions and trigger motor to reverse direction.

A stepper motor with a small gear reduction may work out too, though the step resolution** may be an issue at 10Hz. In that case, a single limit switch might be sufficient. If the stepper driver electronics can sense stalling (from hitting a hard stop), you can even go with no switch at all. Some fancy industrial ones from FESTO I've used do this, but that is massively overpriced and overkill.

Other thoughts:

• If the stepper motor step-resolution is not a limitation, you could also use any rotary-to-linear mechanism, and program the stepper motor's motion profile to compensate for the non-linearity.
• Also take a look at windshield-wiper mechanisms, they have a clever mechanical auto-reverse gear shift arrangement that activates when the motion reaches the ends. That could perhaps be used here.
• With any electronically-controlled motor situation, some controlled acceleration at the ends of motion will probably be necessary, as a theoretical triangle profile has infinite acceleration at the ends.

** For stepper motor resolution and gear reduction considerations, use typical values of 200steps/rev, prior to any gear reduction, and a max step rate of 1000 steps/sec