Compact Assistive Rehabilitation Devices– Concept and Preliminary Function Test O. Ivlev1,2, D. Baiden1, A. Wilkening1,2, C. Koch3, and H.-D. Haas3 1
FWBI Friedrich-Wilhelm-Bessel-Institute Research Company, Bremen, Germany 2 University of Bremen, Institute of Automation, Germany 3 Dr. Paul Koch GmbH, Frickenhausen, Germany
Abstract— Conceptual design of compact light-weight devices for lower extremity motion therapy and rehabilitation is presented. The core of these devices are new inherent complaint (soft) fluidic actuators of rotary type, which generally provide safe and gentle treatment. The actuator compliance can be varied by pressure regulation, which makes soft fluidic actuators very suitable for making the transition from continuous passive motion to active (assistive) behavior during the therapy depending on patient activity. The assistive behavior can be realized without force measurements by means of expensive sensors. Keywords— Assistive motion therapy, rehabilitation robots, soft actuators.
designed. In comparison with the previously developed actuators with pleated rotary elastic chambers (pRECactuator) [6, 7], destined for soft robotic joints, the new (patent pending) actuators utilize other techniques for forming of working chambers. These new types of rotary chambers – “buckled” chamber (bREC) and “coiled” chamber (cREC) – allow construction of “slim” REC-actuators in shape of a flat cylinder, whose diameter is larger than their height. With pREC such slim design is not possible. The initial tests of new “slim” REC-actuators show partly better performances (working torque and angle) as pRECactuators and they are undoubtedly better suitable for integration in rehabilitation devices. The conceptual design of such devices is presented in the following sections.
I. INTRODUCTION The patient-cooperative or assistive rehabilitation robots have obvious therapeutic advantages in comparison with conventional motion therapy devices like continuous passive motion (CPM) machines. It is assumed that patientcooperative strategies will maximize the therapeutic outcome [1], the treatment period can be reduced and the medical costs will decrease. A recent study confirms the effectiveness of the robot assisted therapy in neurorehabilitation [2]. In fact rehabilitation robots are currently barely used in praxis as the less effective, but more simple and budget CPM-machines. By using of inherent compliant, or “soft” actuators, which allow slight deviations from the given position, the human-machine interaction can occur in a gentle and more comfortable manner. Between a variety of existing inherent compliant actuators the soft fluidic (pneumatic) actuators occupy an unique position. In addition to an inherent safety this kind of soft actuators have extremely low weight combined with high force amounts, therefore soft fluidic actuators are predestinated for safe humanmachine interaction, particularly with devices of motion therapy. Instead of elaborate force measurements the working forces can be estimated [3, 4], which makes these devices really simple and cost-efficient. With soft fluidic actuators of rotary type, which are currently being developed [5], compact and light-weight assistive devices for motion therapy and rehabilitation can be
II. MOTION THERAPY DEVICES FOR LOWER EXTREMITY – STATE OF THE ART
The majority of today existing patient-cooperating rehabilitation devices for lower extremity are designed for gait training [1, 2, 8, 10]. The ranges of motion in each joint are restricted according to the task requirements, i.e. about 65° in knee and about 50° in hip. For full-range joint mobilisation, i.e. about 130° in knee and about 100° in hip, as it is often required for immediate post-operative treatment after surgical intervention, various CPM splints are mainly in the use [11]. Compact and portable assistive lower-limb devices for single joints are still missing. There are generally two possibilities to couple a motion therapy device, to be it a rehabilitation robot or a CPMmachine, with a human limb: a) using free linkage or end-point based solution, b) using jointed (motorized) splint or exoskeleton-like solution. The main difference is that in the first case the moving mechanism, i.e. a kinematic chain, and the human limb have only one contact spot, while in the second case a kinematic chain is attached at several points along the user’s limb. The advantages and disadvantage of both solutions are well known and detailed discussed in literature [2, 8, 10, 11]. The end-point systems provide an excellent adjustability to
O. Dössel and W.C. Schlegel (Eds.): WC 2009, IFMBE Proceedings 25/IX, pp. 88–91, 2009. www.springerlink.com
Compact Assistive Rehabilitation Devices – Concept and Preliminary Function Test
the user’s size as well as a long-term comfort and allow multi-axis motion. However the joint stability as well as the control precision of individual joints is very poor. The exoskeleton-like systems can be distinguished in anatomic (kinematically equivalent to the human limb) and nonanatomic, kinematically different with respect to the human limb. The anatomic exoskeletons allow a precise control of individual joints provided that the mechanical axes coincide with the limb axes. Though the long-term comfort for anatomic exoskeletons is better, the user size adjustability is poorer than in non-anatomic systems.
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With the REC-actuators producing considerable torques in the angel area from 0 to 130° the full ranges of motion in knee as well as in hip are achievable. B. “Free-Knee”-Concept If only knee mobilization without hip movements is requested, the device shown in Fig. 2 can be applied. The range of knee motion is admittedly restricted to about 90°, however the nature of lower leg movement is similar to the gentle approach taken by a physiotherapist when manipulating the limb manually immediately after surgical intervention.
III. CONCEPTUAL DESIGN Unlike most of conventional CPM, equipped with linear electrical drive affecting the foot, the soft REC-actuator provides directly the rotational movement in the knee joint. Such mechanical scheme (with the actuated knee joint) is implemented in the Otto Bock Lower Limb CPM L4D/L4KD, although using standard – not soft – electric motors with gears. According to the product flyer, treatment benefits of such mechanics include constant angular velocity over the entire range of motion and minimized anterior tibial translation and joint compression. Conceptual design of two new modular motion therapy devices for lower extremity using slim-line REC-actuators are shown in Fig. 1 (the “full-leg”-concept) and in Fig. 2 (the “free-knee”-concept). Both concepts utilize the constrained (i.e. splint or exoskeleton-like) anatomic solution, whereby the complex leg movement is restricted to only the sagittal plane. Compactness, portability and a low weight should make these devices suitable for hospital use as well as for application at home. A. “Full-Leg”-Concept The simultaneous movement in knee and hip joints is ensured due to mechanical linkage with two passive sliders. The actuation of the hip joint with separate actuators is also possible but not applied because of cost reasons.
Fig. 2 “Free-Knee”-Concept In the device shown in Fig. 2 the disposition of thigh tilting can be adjusted manually; in the more comfortable version the adjustment in the area of required tilt angles from 0 to 60° can be automated by using of additional RECactuators with buckled chambers. This kind of REC can be easy integrated directly under the thigh. Both therapy devices can be applied due to their symmetrical design with two slim REC-actuators sideways for treatment of right or left leg without adaptation. The directdrive soft actuators in the knee joint care for safe physical interaction. The ankle mobilization in both devices can be realized either with separate actuators or through a mechanical linkage as it is usual in CPM-machines. However this cost-saving solution does not allow the immediate ankle-centred assistive therapy.
IV. FIRST EXPERIMENTAL RESULTS A.
Fig. 1 “Full-Leg”-Concept
The preliminary test bed
To perform the preliminary functional tests and to investigate the patient-centred (assistive) control strategies in parallel with development of “slim-line” REC-actuators the proof-of-concept prototype with two (non-slim) pRECactuators have been used (Fig. 3). As a passive load a leg dummy filled with a synthetic material to get a realistic weight of the lower leg is applied. The thigh and the lower
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leg are connected through a single-axis mechanical knee joint from Otto-Bock. The active forces occurring while patient activities (contributing or disturbing) have been simulated manually.
serves for default settings (see Fig. 4.b). Here the user can adjust the operation range or record the end positions of a given motion by moving the device manually. By setting up the patient’s body weight and leg length the weight of the lower leg is calculated and therefore gravitation compensation (see section V) works more precisely. Furthermore there is the opportunity to set a therapy timer for stopping the device automatically. The main menu (see Fig. 4.a) only contains the most important buttons for setting motion controls as well as assistive force and velocity by a slider bar. An analogue gauge shows the actual position and the limits of motion while the desired moving direction is indicated by an arrow to give the patient an orientation.
Fig. 3 Test-bed with artificial knee joint and pREC-actuators B.
Control unit
To allow a rapid prototyping of control algorithms, the “hardware-in-the-loop” concept is followed by using the real time development environment of MATLAB/Simulink and dSPACE-equipment. Implemented control strategies are compiled to run on the dSPACE digital signal processor card which is installed in a standard Windows PC. ControlDesk software is a tool to adjust model parameters and to display the actual operating status. The technical look is transformed into an intuitive graphical user interface by merging additional program code as a combination of C and Python language. According to the current state of the art a touch screen monitor is used to permit a versatile configuration of the interface. The monitor is mounted on top of a mobile rack which contains the IPC (Industrial-PC) and offers room for power supplies, I/O connector panel and a 10 litre pressure reservoir which serves as air buffer. The touch-sensitive interface was designed to be self descriptive and easy to use even for untrained users. The buttons are large, finger friendly and clearly labeled so elderly people could handle the device also by themselves, possibly even at home. Every section is separated by an own frame with associated help buttons which call a pop-up window with detailed instructions. Lots of attention was paid to catch wrong user inputs i.e. starting the device without pressure approval or typing in parameters out of range. Every inappropriate input is notified by an acoustic feedback respectively a text message. One of the two interfaces
a) b) Fig. 4 Graphical user interface; a) main menu, b) settings menu. Visual feedback shall motivate the user to provide more own muscle activity to improve the healing process. The patient’s efforts are detected and interpreted before showing them as a colour bar.
V. “ASSIST-AS-NEEDED” CONTROL CONCEPT To ensure an assistive behaviour the “Assist-as-Needed” (AaN) model-based force controller suggested in [3] for conventional pneumatic actuators was adapted and implemented for REC-actuators. Due to the fact, that the inherent compliance of REC-actuators is provided by air compressibility as well as by chamber elasticity, a really comfortable assistive behaviour has been achieved in the experiments. The experimental results reported in this section describe the results using the developed AaN controller. The control scheme has a cascade structure with a nonlinear model-based torque control in the inner loop. By
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applying this concept an assistive force of the robot will only be generated if the patient’s strength is insufficient to accomplish the desired motion. The implemented control concept is based on a point to point movement, thus no strict desired trajectory is given. The patient just needs to reach a desired target point in a specific time. If a target is reached the next target point will be defined. Consequence of a movement against the target course will be a smooth increasing of force to bring the patient gently to right direction. Sufficient patient’s movement, i.e. enough human strength, will decrease the assistive force of the robot to zero. By means of the subordinate model-based torque control a gravitation compensation of the patient’s lower leg and the mechanics is achieved. Thus, even in case of enough patient’s strength the weight of his lower limp and of the device will be compensated. Fig. 5 shows the experimental results using the AaN controller, with a passive continuous motion in the first and the AaN motion in the second segment, whereby the patient’s strength has been simulated manually.
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Fig. 5 Experimental results using the AaN controller; patient behaves passive in the first and active in the second segment.
In the first segment (before approx. 55 s) no active strength of the patient was generated and due to that a passive continuous motion is incidental. One can see that the assistive torque is increasing until the desired target point is reached. A sufficient strength in the second segment (after approx. 55 s) causes a decreasing of torque, i.e. assistive force of the robot. Target overshoot leads to a smooth increasing of torque and consequence is a patient’s motion to the new correct direction.
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ACKNOWLEDGMENT The concepts of new motion therapy devices with RECactuators were detailed discussed with the cooperation partner Dr. P. Reize and M. Mahner from Clinical Centre Stuttgart within the cooperative research project KoBSAR “Compact assistive/restorative motion therapy devices of new generation, based on fluidic soft actuators with rotary elastic chambers”. Product design renderings are produced by :i/i/d Institute of Integrated Design, Bremen.
REFERENCES 1.
Riener R. Patient-Interactive Robots for Arm and Gait Rehabilitation, Technical Aids for Rehabilitation – TAR 2007, Berlin, 2007, pp.2930 2. Waldner A., Werner C., Hesse S. Robot assisted therapy in neurorehabilitation. Europa Medicophysica, Vo. 44, Suppl.1 to Nr. 3, 2008, pp.1-3 3. Wolbrecht E.T., Leavitt J., Reinkensmeyer D.J., Bobrow J.E. Control of a Pneumatic Orthosis for Upper Extremity Stroke Rehabilitation. Proc. 28th IEEE EMBS Ann. Int. Conf., Aug.30-Sept.3, NYC, 2006, pp. 2687-2693 4. Vanderniepen I., Van Ham R., Naudet J., Van Damme M., Vanderborght B., Versluys R., Lefeber D. Novel Compliant Actuator for Safe and Ergonomic Rehabilitation Robots - Design of a Powered Elbow Orthosis. IEEE 10th Int. Conf. on Rehab. Robotics (ICORR’07), 2007, pp. 790 – 797 5. Ivlev O. Soft Fluidic Actuators of Rotary Type for Safe Physical Human-Machine Interaction. Technical Aids for Rehabilitation – TAR 2009, Berlin, March 18-19, 2009 6. Ivlev O., Mihajlov M., Gräser A. Modular Multi-Sensory Fluidic Actuator with Pleated Rotary Elastic Chambers; 4th IFAC Symposium on Mechatronic Systems, Sept. 12 - 14, Heidelberg, Germany; 2006. 7. Kargov A., Breitwieser H., Klosek H., Pylatiuk C., Schulz S., Bretthauer G. Design of a modular arm robot system based on flexible fluidic drive elements. IEEE 10th Int. Conf. on Rehabilitation Robotics (ICORR'07), Noordwijk, NL, June 12-15, 2007 8. Wearable Robots: Biomechatronic Exoskeletons. Edited by J. L. Pons, 2008, 338p. 9. Knestel M., Hofer E.P., Klee B. S., Rupp R. The Artificial Muscle as an Innovative Actuator in Rehabilitation Robotics. Proc. 17th IFAC World Congress (IFAC), Seoul, Korea, July 6-11, 2008 10. Dollar A.M., Herr H. Lower Extremity Exoskeletons and Active Orthoses: Challenges and State-of-the-Art. IEEE Trans. on Robotics, Vol. 24, 1, 2008, pp.144-158 11. Salter R. Continuous Passive Motion: A Biological Concept for the Healing and Regeneration of Articular Cartilage, Ligaments, and Tendons: From Origination to Research to Clinical, 1992, 419p Author: Dr. Oleg Ivlev Institute: Friedrich-Wilhelm-Bessel-Institute Research Company and University of Bremen, Institute of Automation Street: Otto-Hahn-Allee, NW1 City: Bremen Country: Germany Email:
[email protected];
[email protected]
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