Soft motion planning – Managing velocity, acceleration and jerk

The most basic feature of a robot is to be able to move, that motion should be controlled in a way that the required displacement is made in a required time, but also controlling velocity, acceleration (and therefore force) and comfort, (at least to the eye of the viewer).

There are many possible strategies to define motion control laws, with more or less detail, the least controlled, just moves a cursor at a constant velocity, but we can also introduce an acceleration ramp, witch can be at a constant rate or can evolve at a rate called jerk. The most complex algorithms require more processing power but also allow greater dynamics with lower effort from drives and mechanics, and also greater comfort.

We will describe the calculations required for an implementation that can be handled by a 32 bit microprocessor with math co-processor (ARM Cortex M3) in under 50ns, intended to give a good stability for robot manipulators with elastic transmission.

Introduction

In the development of a robot controller, the motion control routines are of crucial importance, more so when the robot’s structure and actuators are intended to have a not negligible elasticity.

This article will describe the development, of the laws of motion and their implementation as an algorithm. Finally, we will demonstrate the working system with a stepper motor and demonstrate the importance of such an algorithm in elastic structure robot control.

Fernando Figueiredo
SMILE.TECH – ROBÓTICA, LDA / ISPGAYA – Instituto Superior Politécnico Gaya

Nelson Neves
WIDESKILLS – Inovação, Projetos e Soluções, Lda. / ISPGAYA – Instituto Superior Politécnico Gaya

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