Analysis and Synthesis of Parallel Robots for Medical Applications

M.Sc. Thesis - Technion-Israel Institute of Technology

Mechanical Engineering

Nabil Simaan

Supervisor: Prof. M. Shoham.


Project Description (1997 - 1999)

This thesis deals with the development of a mini parallel robot for medical applications. The medical applications considered are manipulation of a laparoscopic/Arthroscopic camera in minimally-invasive surgeries. These applications require limited workspace. Consequently, the parallel robot architecture is suitable for these applications and provides a robot which is more compact than the usual serial robots.

A comparison between different architectures for the same task is presented in this work with results obtained for dimensional synthesis. A working prototype of an RSPR3 parallel robot was dimensionally synthesized, built, and actuated in position control for validating the results of our design.
The design features a robot with a minimal number of singularities inside its workspace.

The prototype is currently being experimentally tested for knee arthroscopic surgery and as an integrated tool for registration and surgical assistance in TKR (Total Knee Replacement).

The RSPR3 Mini-Parallel Robot

This manipulator consists of three identical kinematic chains connecting the base and the moving platform. Each chain contains a lower link rotating around a pivot perpendicular to the base platform and offset-placed from the center of the base. At the other end of the lower link, a prismatic actuator is attached by a spherical joint. The upper end of the prismatic actuator is connected to the moving platform by a revolute joint. The axes of the revolute joints constitute an equilateral triangle in the plane of the moving platform, Fig. 1.

The design process included singularity analysis of the architecture. This yielded a robot with a minimal number of singularities inside its workspace. One of the features of this robot is its capabilities to perform 90 degrees rotation about the vertical axis and to align one of the linear actuators with the plane of the moving platform without having parallel singularity, in which, the moving platform loses constraint (gains uncontrollable degrees of freedom). The rotation of 90 degrees about the vertical axis and the alignment of one of the prismatic actuators with the plane of moving platform is known in the literature [1-5] to cause parallel singularity in the Stewart-Gough 3-3 and 3-6 platforms.

You can see animated-gifs of the robot performing random motions and 90 degrees rotation about the verical axis*.

If you have a fast internet connection you can choose the following links:

Random motions - medium resolution
 

90 degrees Rotation - medium reoultion

If you have a slow internet connection you can choose the following links:

Random motions - low resolution

90 degrees Rotation - low reoultion

* In these films we use the Windows version of the position control software developed by D. Glozman for using the robot as a registration tool.

The RSPR3 Parallel robot

Figure 1: The RSPR3 mini-parallel robot

Further development
The RSPR3 prototype is currently in a revision phase and adaptations for testing it as a medical assistant manipulating a camera in Arthroscopic knee surgery, Fig, 2.

Figure 2: The RSPR3 manipulating an arthroscopic camera

Acknowledgments
We would like to express our thanks to Dr. Moshe Roffman and Dr. Beni Bernfeld of Carmel Hospital at Haifa for thier advise on the medical application and assistance in the preliminary experiments. This project was partially supported by the Fund for Promotion of Sponsored Research at the Technion.
References
  1. K. H. Hunt, “Structural Kinematics of In-Parallel-Actuated Robot-Arms,” ASME J. Mechanisms, Transmiss. Automat. Design, Vol. 105, pp. 705-712, 1983.
  2. E. F. Fichter, “A Stewart Platform-Based Manipulator: General Theory and Practical Construction.” Int. J. Robot. Res., Vol. 5, No. 2, pp. 157-182, 1986.
  3. J. P. Merlet, “Singular Configurations of Parallel Manipulators and Grassmann Geometry,” Int. J. Robot. Res., Vol. 8, No. 5, 1989.
  4. J. P. Merlet, “Parallel Manipulators, part 2: Singular configurations and Grassman geometry”. INRIA research Report No. 791, February 1988.
  5. R . Ben-Horin, Criteria for Analysis of Parallel Robots. Ph.D. dissertation, Technion, Israel, 1997.
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