In addition to the ubiquitous serial industrial robots, other types of manipulators are also available, called parallel robots. A serial robot is basically a series of links connected by motorized joints, while a parallel robot is comprised of several series of links, with most of their joints not motorized. “Parallel Project of CoRo Lab, at the École de Technologie Supérieure, Montreal, Quebec, Canada
Parallel robots can be faster, more rigid and/or accurate than serial robots. Like almost all motion simulators, most rapid pick-and-place robots are parallel robots. Many precise positioning devices are also parallel robots.
Through his website ParalleMIC and his research on the kinematic analysis and design of parallel mechanisms, Professor Ilian Bonev is renowned in the area of parallel robotics. He leads most of the R&D work involving parallel robots conducted at the CoRo laboratory, where the work breaks down into three categories: theoretical work, mechanical design and simulation software development.
This video shows DexTAR, a double-SCARA parallel robot, which is probably the best pedagogical example of a parallel mechanism. Both serial and parallel singularities are demonstrated. DexTAR crosses serial singularities (i.e., changes working modes) in order to enlarge its workspace. It can also cross parallel singularities, but the control strategies required to do so in an optimal way are very complicated. Besides, there is very little advantage of crossing parallel singularities (i.e., changing assembly modes)
The following are the main theoretical areas Professor Bonev is interested in:
- study of the singularities and workspace of parallel robots;
- geometric design of new parallel mechanisms with large workspace and few singularities.
This type of research is particularly well suited for students interested in geometry, and projects can be purely theoretical or combined with a practical component (experiments on an existing prototype or development of a new one).
The following articles clearly illustrate the bases of theoretical projects:
- Rakotomanga, N., et Bonev, I.A., “A 3-RPR parallel mechanism with singularities that are self-motions”, Journal of Mechanisms and Robotics, Vol. 2, No. 3, 2010.
- Bonev, I.A., Yu, A., et Zsombor-Murray, P., “XY-Theta positioning table with parallel kinematics and unlimited theta rotation”, IEEE International Symposium on Industrial Electronics, Montréal, Qc, Canada, 9-13 juillet 2006.
At the practical level, Professor Bonev is mainly interested in the mechanical design of new parallel robots with large workspace and high absolute accuracy (see Precision Roboticssection) or for very specific applications. In both cases, industrial grade prototypes are designed and produced at the ÉTS. The controllers for these prototypes are generally developed by Professor Pascal Bigras (see Control section).
The robots are designed using CATIA, SolidWorks and ADAMS software. Parts are machined at the Laboratoire institutionnel de fabrication de l’ÉTS (ÉTS’ Institutional Manufacture Laboratory) which houses 21 machines, including seven NC machining centres. Following proper training, CoRo members are able to use most of these machine-tools independently.
The first prototype developed at the CoRo laboratory is an XY-Theta precision positioning table, called PreXYT (for Precision XY-Theta table). This is a new singularity-free three-degrees-of-freedom parallel robot with very simple kinematics. The robot was designed for the precision positioning of silicon wafers, and its effector can cover a circular zone 170 mm in diameter, with any orientation between -17° and 17°, and an absolute positioning error under 0.050 mm.
The following documents describe the robot in detail:
- Bonev, I.A., “Planar parallel mechanism and method”, American Patent No. 7 707 907, filed on November 17, 2006; delivered on May 4, 2010.
- Yu, A., Bonev, I.A. and Zsombor-Murray, P., “New XY-Theta positioning table with partially decoupled parallel kinematics”, IEEE International Symposium on Industrial Electronics, Montréal, QC, Canada, July 9-13, 2006.
- Joubair, A., Slamani, M. and Bonev, I.A., “A novel XY-Theta precision table and a geometric procedure for its kinematic calibration”, Robotics and Computer-Integrated Manufacturing, 2011.
PreXYT, XY-Theta parallel robot (video)
DexTAR, XYZ parallel robot (video)
The second prototype, called DexTAR (for Dextrous Twin-Arm Robot), is a rapid pick-and-place XYZ robot, based on a 5-bar mechanism. Its originality lies in the fact that the robot can reconfigure itself dynamically to maximize its workspace (by crossing serial singularities).
The following article describes the robot in detail:
- Campos, L., Bourbonnais, F., Bonev, I.A. and Bigras, P., “Development of a five-bar parallel robot with large workspace”, ASME 2010 International Design Engineering Technical Conferences, Montréal, QC, Canada, August 15-18, 2010.
MedRUE, six-degrees-of-freedom parallel robot (video)
The third prototype is a six-degrees-of-freedom robot called MedRUE (for Medical Robot for vascular Ultrasound Examination), which is used to analyze the arteries of the lower limbs. The robot will perform diagnoses of the stenosis using an ultrasound probe. This project, which is currently under development, is being carried out in collaboration with the Hôpital Notre-Dame, a part of the Centre hospitalier de l’Université de Montréal (CHUM) network.
The follow documents describe the robot in detail:
- Lessard, S., Bonev, I.A., Bigras, P., “Parallel manipulator”, American Patent No. 7 673 537, filed on June 2, 2008, Delivered on March 9, 2010.
- Yen, A.K.W., Asservissement en position d’un manipulateur robotique pour l’échographie 3D des artères des membres inférieurs (Servo position control of robotic manipulator for 3-D echography of lower limb arteries), Master’s thesis, École de technologie supérieure, 2011.
The fifth prototype is a rotary hexapod called MicARH (for Micropositioning Agile Rotary Hexapod). This project is currently under development.
MicARH, rotary hexapod for micropositioning (video)