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Stewart Platforms

Table of Contents

The goal of this project is to provide a Matlab/Simscape Toolbox to study Stewart platforms.

The project is divided into several section listed below.

1 Simulink Project (link)

The project is managed with a Simulink Project. Such project is briefly presented here.

2 Stewart Platform Architecture Definition (link)

The way the Stewart Platform is defined is explained here.

All the geometrical parameters are defined including:

  • Definition of the location of the frames
  • Location/orientation of the limbs
  • Size/inertia of the platforms and the limbs

Other parameters are also defined such as:

  • Stiffness and damping of the struts
  • Rest position of the Stewart platform

3 Simscape Model of the Stewart Platform (link)

The Stewart Platform is then modeled using Simscape.

The way to model is build and works is explained here.

4 Kinematic Analysis (link)

From the defined geometry of the Stewart platform, we can perform static analysis such as:

  • Jacobian Analysis that links the velocity of each limb to the velocity of the mobile platform
  • Static Forces Analysis that links the forces applied by each limb to the resulting force/torque applied to the mobile platform

From the strut stiffness, we can also perform a Stiffness Analysis that consists of determining the Stiffness matrix and Compliance matrix of the Stewart platform from the geometry.

All these analysis are described here.

5 Identification of the Stewart Dynamics (link)

The Dynamics of the Stewart platform can be identified using the Simscape model.

It is possible to:

  • Determine the dynamics from the actuators to the various sensors included in the Stewart platform
  • Extract State Space models for further analysis / control synthesis
  • Extract the Resonant Frequencies, Modal Damping, and associated Mode Shapes

The code that is used for identification is explained here.

6 Control

The use of active control for Stewart platforms is a wide subject. Many aspect can be studied.

The sensors used is of primary important. We can have:

  • Sensors located in each strut: relative motion, force sensor, inertial sensor
  • Sensors measuring the relative motion between the fixed base and the mobile platform
  • Inertial sensors located on the mobile platform

The control objective can also vary:

  • Reference Tracking
  • Active Damping
  • Vibration Isolation

The Control for Stewart platforms is here studied in the following files:

  • Active Damping (link). The use of different sensors are compared for active damping:
    • Inertial Sensor in each strut or fixed to the mobile platform
    • Force Sensor in each strut
    • Relative Motion Sensor in each strut
  • Motion Control (link). Different control architectures (centralized and decentralized) are compared for the position control of the Stewart platform.
  • Vibration Isolation (link)

7 Cubic Configuration (link)

The cubic configuration is a special class of Stewart platform that has interesting properties.

These properties are studied in this document.

8 Bibliography (link)

Many text books, PhD thesis and articles related to parallel robots and Stewart platforms are gathered in this document.

Author: Dehaeze Thomas

Created: 2020-08-05 mer. 13:27