Force Feedback Mechatronics in Medecine, Healthcare and Rehabilitation J.P. Friconneau 1, P. Garrec 1, F. Gosselin 1, A. Riwan 1, 1 CEA-LIST DTSI/SRSI, CEN/FAR BP6, 92265 Fontenay-aux-Roses, France jean-pierre.friconneau@cea.fr Keywords: Mechatronics, Force feedback, Intelligent power assist, surgery, rehabilitation Abstract Robotics force feedback technologies provide the feeling of directly holding remote instruments. This is true in nuclear applications where remote operations are required due to the hazardous environment. This is also true in surgery applications, in particular in Minimally Invasive Surgery (MIS), when organs cannot be accessed directly. During surgery procedures, the surgeon should have the feeling in his hands of holding directly the surgical instruments interacting with the patient. Both applications emphasize therefore same type of needs for high performance force feedback Mechatronic components. We aim therefore benefits from research and development results from the field of Mechatronics for Telerobotics to provide good basis for improvement in medical technology. Many similarities could also be pointed out with various other applications requiring force feedback features for gesture guidance or training: medical learning course with help of haptic and virtual reality technologies, kinaesthetic and physical assist device for rehabilitation, aged people or disable people. 1. INTRODUCTION Most common use of robotics technologies mainly stands for automotive and production line applications where robots mainly execute continuously pre-programmed tasks (Fig 1.a). When considering Telerobotics (Fig1.b), two main features differ: - Human is in the loop of the robot control and interact in real time, task are not preprogrammed. - Force feedback feature is required to operate remotely and interactively. In Telerobotics, main scope of the force feedback feature is to simulate the mechanical behaviour of the tool. This is also true for endoscopic surgery, in particular in Minimally Invasive Surgery (MIS), which has deeply changed surgical practice since 10 years [3]. Absence of direct viewing and direct access to patient body associated with reduced dexterity and sensory feedback calls for Telerobotics. With several similarities, in Virtual Reality (V.R.) applications haptic interfaces (Fig 1.c) are used as force reflecting devices allowing to touch, feel, manipulate, create, and/or alter simulated D-objects in a virtual environment. Virtual reality with force feed back is used to train physical skills aiming to minimize use of experiments on animals or cadavers as well as to mock-up digital interactive prototypes directly from CAD databases.
Finally, active devices such as Intelligent assist device (IAD) or collaborative robots known as Cobots (Fig 1.d), deals with active power assistance, motion guidance and advanced interaction control where user and robotics system share control by means of virtual mechanisms [8]. When considering physical assistance to enhance human performances, Robots can assist directly the operations to position accurately surgical tool (avoiding vital regions) when the surgeon drives the same tool sensitively by means of video and force feedback feature. Digital techniques enable to set up a wide range of assistances in such a scheme. For rehabilitation purposes, power assistance computer controlled (called Ergonomic assist device) gives new feature for the patrician. This device improves trajectories and motion behaviour by means of power assistance computer controlled. The user is able to control and co-ordinate movements with help of this power assistance. Fig 1.a. Robotics Fig 1.b. Tele Robotics Fig 1.c Virtual Reality - Haptic Fig 1.d. Collaborative Robots Fig1. Force Feedback Human Robot interaction scheme. Field of application of force feed back techniques has thus grown significantly. From Telerobotics to V.R. applications, design of a force reflective device assumes careful analysis of several tradeoffs to emphasis the realism.
2. MECHATRONICS TRADEOFFS IN HUMAN ROBOT INTERACTION. When considering physical human-robot interaction, first reference comes from Telerobotics applications such as nuclear, deep sea or planetary exploration. Telerobotics features induce capacity of the robotic system to permanent interact with the user. In such case, the environment of the robot is not well known or structured, the intervention task even prepared cannot be automatically executed and the task is performed by the user through the robot. Standard scheme in Medical field deals with Telerobotics in minimal invasive surgery where the surgeons cannot access hands on in the field of operation because of the size of the access holes. The practitioner should operate his set of surgery tools remotely through a force feedback master/slave system. Advanced techniques and technology have been developed so far (historically for hazardous environment applications) to enhance capacity to overcome limitation due to the remote conditions. Theses technologies intend to enhance direct human-robot interaction despite of limitation due to the configuration: time delay, robot sensitivity, real time computations, friction, The global performances of the system come from a combination of individual system performances in addition with integration issues. One of the key factor with is kind of systems is the performances of the robotic joint itself combining mechanics, electronics and software. This stands for motion actuation and motion sensitivity: In a good force feedback input device [13], balance should be considered between force generation to resist to user motion and force sensitivity to feel user intention. Special attention should be considered in the design of the force transmission along the robot structure. A large consensus exists on the characteristics a good input device must exhibit [10] [11] [12]. A. System tradeoffs Mechanical design Human factors / ergonomics Computation Contact rendering Geometry rendering. Control properties Stability (passivity principle /energy dissipation) Quality of force feedback B. Mechanical design tradeoffs Free in free space Low Inertia Manipulability, dexterous workspace Smooth transmission/back drivability (Low friction) Strong in reaction space Degrees of freedom Singularities (force/motion uncontrollable) Free of backslash High stiffness Force / torque at end point (continuous/peak)
4. SYSTEM DESIGN ISSUES IN HUMAN ROBOT INTERACTION. Design of a force feedback robotic system in Medicine, healthcare and rehabilitation reveal system design issues due to various configuration schemes (Fig 1). In each case, quality of force sensation drives for high quality at joint level in both human robot interaction directions (input and output). The system should exhibit symmetric performances when operated by the user. In human robot interaction, fidelity in visual feedback requires fidelity in trajectory therefore for perfection in mechanical transmission with high stiffness and low inertia. High fidelity in force feedback and symmetry in force transmission imposes very low friction (stick/slip) with high mechanical efficiency. High fidelity of mechanical behaviour of the human robot interaction must be as high as possible. In practice, efficiency of the mechanical structure comes from extensive use of basic component such as levers, connecting rods, expanding parallelograms, cables, metallic friction tape, belt, etc Design of such robotic device is not trivial, constraints stands for power transmission through complicated kinematics (multi-body/ multi-link mechanical structure), wide range of motion, static balancing of full system in various configurations, limited mechanical play. In addition, the system should resist to unexpected overload due to the non predictable interaction situation. Standard performances in this field stand for force feed back at 2daN level with some pick at 4 dan. Then application driven requirement such as sterilisation in medical field must be satisfied. Finally, most important issue is safety in human robot interaction. 7. CONCLUSION This paper gives some clarifications to understand main drivers of interactive robotic devices design activities. Meeting design requirement requires adequate tradeoffs in addition with extensive use of advanced mechatronics technology. Theses are the key factors of the success. Telerobotics mechatronics technology developed in the field of hazardous environment since many years is beginning to be used in the medical field. First generation of Telerobotics devices involving force feed back human interaction requires however significant improvements to be adapted to the various application requirements (surgery, rehabilitation, ) in order to increase the patient benefits. This evolution calls for medical systems whose performance depends on the quality of the input device allowing the practitioner to control the system. References 1. J. Heinzmann, A. Zelinsky, Quantitative safety guarantees for physical human-robot interaction., The international jounal of robotics research, Vol.22, No. 7-8 2. D. Surdilovic, R. Bernhardt, L. Zhang, New intelligent power-assist system based on differential transmission, Robotica (2003) volume 21, pp. 295-302. 3. J-P Friconneau,, M. Karouia, F. Gosselin, Ph. Gravez, N. Bonnet, P. Leprince, Force feedback master arms, from telerobotics to robotics surgery training, Proceedings IEEE Conference on Medical Robotics and computer Assisted Surgery, Paris, 2002, pp. 31-36.
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