Virtual reality tool for Orthoglide parallel robot.

Rat, Nadia Ramona ; Gogu, Grigore ; Stan, Sergiu Dan 等

1. INTRODUCTION

The parallel robots are mechanisms with kinematics closed chains, composed by an end-effector (the mobile platform) with n degrees of freedom, connected to the fixe base by two or more kinematical chains called limbs or legs. A simple or a complex kinematic chain can be associated with each limb (Gogu, 2008).

The Virtual Reality (VR) immerses the user in a three-dimensional (3D) environment that can be actively interacted and explored (Halliday, 1994).

Virtual reality environment tool is used by many researchers in design, development and manufacturing of the robotic industry (Stan et al., 2008).

Using the virtual reality simulation with a virtual robot, we can observe a three dimensional design and the real-time behavior of the robot; that fact is relatively new and allows testing the robot before accomplishment a physical implementation. In this way, we can save important resources (money and time) and we can adjust the various problems without affecting the physical robot.

This paper presents the necessary steps to develop the virtual environment for kinematic simulation, starting from the SolidWorks model of Orthoglide parallel robot.

Orthoglide is a 3DOF parallel robot (Wenger and Chablat 2000) with three coupled motions of type 3PRPaR (3-Prismatic-Revolute-Parallelogram-Revolute), composed by a mobile platform connected to the fixed frame by three kinematic chains presented in figure 1 (Gogu, 2004).

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2. ALGORITHM FOR DEVELOPMING A VR APLICATION BASED ON SOLIDWORKS CAD MODEL

This approach has a great advantage to making possible to observe the behavior of the robot in virtual medium using the interface SolidWorks--SimMechanics--MATLAB/Simulink Virtual Reality.

The first step is to make the CAD model of Orhoglide parallel robot in SolidWorks environment.

Once the CAD model is done, the next step is to export the model in SimMechanics environment for transposition in MATLAB/Simulink environment.

For a better comprehension of the needed steps for obtaining the VR model an algorithm is presented in figure 2.

The inertia proprieties and the coordinates of the joints were determined automatically when the CAD model was imported from SolidWorks in Matlab/Simulink environment. Inputs for the model can be: the position, velocity or acceleration of actuated joints or the generalized forces.

In this paper, the input was chosen to be the speed of all three actuator joints of the Orthoglide parallel robot.

In Matlab Simulink environment, the three parallel links connected at the mobile platform can be seen in figure 3.

Figure 3a presents the SolidWorks model of the Orthoglide parallel robot. SimMechanics model of Orthoglide is presented in figure 3b.

The dynamic model of Orthoglide parallel robot is presented in figure 3c. We can see the three links (noted with arm 1 to 3) connecting the base (noted with batiu) and the mobile platform (noted platforma). A parallelogram loop can be observed in each limb (figure 3d).

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In this step we can verify the validity of the SolidWorks model. This model is valid if a direct correspondence exists between the links and the kinematic joints in figures 1 and 3d (ex: a revolute joint from figure 1 need to be also a revolute joint in figure3d). If the SimMechanics machine model is set up correctly, then we can go to the next step and create the virtual reality environment.

3. VIRTUAL REALITY TOOL

Once the dynamic model is set up in MATLAB/Simulink environment, the next step is to make the Virtual Reality environment imported from SolidWorks model. To do this, we need to export the SolidWorks model like VRML files and with few modifications the Virtual Reality environment for Orthoglide parallel robot can be obtained (figure 4).

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In figure 4, we can see how the dynamic model from figure 3 was modified to obtain the connection with the Virtual Reality environment. A special attention must be paid to use the same notations in the dynamic and Virtual Reality models (figure 4 and figure 5).

4. CONCLUSIONS

A Virtual Reality (VR) interface for the control of Orthoglide 3PRPaR parallel robot has been presented in this paper. The interface for high level control presented in this paper was verified and tested for Orthoglide parallel robot and results were presented in MATLAB/Simulink and SimMechanics environment. If we need to feel the behaviour of the robot, a Joystick can be easily integrated in the model. A control model can also be added to get a complete view of robot behavior.

5. REFERENCES

Halliday, S., Green, M., (1994) A Geometric Modeling and Animation System for Virtual Reality, Virtual Reality Software and Technology (VRST 94), 71-84, Singapore, August 1994.

Gogu, G. (2008) Structural Synthesis of Parallel Robots, Part 1: Methodology, Springer.

Gogu, G., (2004). Structural synthesis of fully-isotropic translational parallel robots via theory of linear transformations, European Journal of Mechanics /A--Solids, vol. 23, pp. 1021-1039.

Wenger, P.; Chablat, D. (2000). Kinematic analysis of a new parallel machine tool: the Orthoglide. In: Lenarcic J, Stanisic ML (eds) Advances in Robot Kinematics. Kluwer Academic Publishers, pp 305-314.

Stan, S.-D.; Manic, M.; Balan, R.; Lapusan, C. (2008) IG3pR-VRI, a Novel Virtual Reality Robot Interface for Isoglide3 Parallel Robot, 13th IEEE International Conference on Emerging Technologies and Factory Automation, Hamburg, Germany.