Rapidly developing complex machines
Tom Shelley reports on hardware and software that enables robotic and other equipment to be more quickly developed, particularly for medical applications
Pioneering use of hardware and software is driving the development of haptic force-feedback mechanisms, which could prove highly beneficial in medicine and robotics.
The means lies in rapid control prototyping using modular electronic control boards, which can, among other things, turn Windows PCs into highly stable real-time controllers,
The technology comes out of a methodology to develop a range of engineering models to help train engineers in the gentle arts of devising mechatronic control strategies.
This has led on to the development of more sophisticated devices for robotic research and inevitably into real-world commercial products, with applications as varied as training surgeons using virtual reality techniques; improving stroke rehabilitation therapy; controlling fleets of miniature airship UAVs; and a system that allows authors to sign books ‘remotely’.
Quanser is a 35-member strong consulting company based at Markham, near Toronto, Canada. Chief technology officer Dr Jacob Apkarian, originally an assistant professor at the University of British Columbia, founded it. The basic tools are hardware in the loop PCBs and special software called WinCon. This runs MathWorks Simulink in real time on a PC, to which the board is connected. The company also has boards that will interface with The MathWorks xPC Target and National Instruments LabVIEW RTX and RT-LAB.
The boards have provision for various sensor and encoder inputs, and pulse-width modulated motor outputs, and allow a control application to be modelled in software. This can then be tested immediately in hardware, without the need to build a full-sized machine.
According to director of international sales Martin Lord, the company also has some “tricks” of its own, such as a means of synchronising a Windows PC clock with the rather more stable and accurate clock on one of its boards, so an embedded or non embedded PC can be turned into a stable, real-time control system.
This methodology has led to the development of a substantial number of systems, on which students can learn how – and how not – to implement control strategies on systems as varied as tower cranes, autonomous mobile robots, multi-rotor helicopters, magnetic levitation systems and haptic interfaces. Professor Tim Salcudean at the University of British Columbia invented some of these last devices. As well as translating the movements of a human hand and arm into robot instructions, they also provide force feedback on what the robot is encountering. Salcudean originated two of these devices: a twin pantograph robotic motion effector, with three degrees of freedom; and a six degrees of freedom haptic wand.
The pantographs in the robotic effector, which are made of carbon fibre, are driven by two DC motors at the base joints. The business ends of the pantographs are linked together to a handle that can be rotated through 360 degrees unhindered. Optical encoders monitor motor shaft positions.
The six degrees of freedom wand also has two pantographs, but mounted in such a way as to allow for three translations and two rotations - pitch and roll. Each pantograph is driven by two DC motors at its shoulder and another more powerful motor at its waist, along with a recently added extra motor to allow control of the sixth, yaw degree of freedom for a complete emulation of the human arm. Accuracy is to better than 10 microns, stiffness is up to 6N/mm, and the device is sensitive to small forces and surface texture. The company has also developed its own, high-force three degrees of freedom haptic interface, called the Mirage, for surgery and dentistry. By interfacing these to actuation systems through a linear amplifier, it is possible to diminish the actual movements of the hand in situations such as micro-surgery; or amplify them, such as in the remote handling of heavy objects in the mining industry.
Using these and other machines developed using the rapid prototyping technology, it is possible to remotely write on a piece of paper or a sponge. This is not possible without force feedback. Another demonstrated application is to remove sections of banana skin surgically, without damaging the soft interior.
“These are not designed as end products,” says Quanser’s Martin Lord.
Having established that an idea works, researchers are expected either to go back to the company for tools to turn it into a commercial application or, if they wish, have Quanser port the control strategy onto a particular machine or robot.
Another application is to develop an intelligent upper limb stroke rehabilitation robot. This project is being run in conjunction with the Toronto Rehabilitation Institute and the University of Toronto Department of Occupational Science and Occupational Therapy. Their researchers – and others in the UK at Sheffield Hallam University, using different technology – have found that it is beneficial to give rehabilitation patients visual feedback on their progress, in order to motivate them to greater effort. Providing force feedback – either to assist limbs that cannot at once be moved on their own, or force resistance to push against – was also helpful. Such techniques could also help the able-bodied to improve their physical skills.
Even more remarkable is a small airship UAV research package. Airships, both UAVs and largerm are notoriously difficult to control because their operators must consider the effects of power input and control surfaces, as well as the impact of wind pressure and varying buoyancy resulting from changes in the weather. There is also an aspiration to be able to launch fleets of these. The package offered by Quanser comprises a 5+1 degrees of freedom blimp and a dual CPU avionics control board.
The company’s latest development is a new software suite called QuaRC, which runs Mathworks Simulink. This is real-time multi core and multi threaded, to take advantage of latest processing developments. Toolboxes are available for use with the CRS and Mitsubishi PA10 robots, and the various Quanser haptic devices. Interfaces so far released are for Windows and QNX plus Ethercat and dynamic reconfiguration support. RTX, INtime, Integrity, VxWorks, RT Linux and RT Sun Java are either planned or under consideration.
* The methodology combines use of software and direct interfaces to modular hardware boards to quickly establish and then test hardware machine control strategies before building whole machines
* Already well established as a means of quickly developing devices for practical classes in control engineering, it is now moving upwards into academic and industrial research
Text: The most immediate applications are in telerobotics, with one already in commercial use and others under development for the medical sector
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