MECHATRONIC DESIGN IMPLEMENTATION FOR 6-DOF STATIONARY LOWER LIMB REHABILITATION EXOSKELETON ROBOT

THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 701 MECHATRONIC DESIGN IMPLEMENTATION FOR 6-DOF STATIONARY LOWER LIMB REHABILITATION EXOSKELETON ROBOT Javlonbek Rakhmatillaev2, Umidjon Takabaev2, Nodirbek Kimsanboev3 1Department of mechatronics and robotics, Andijan state technical institute, Andijan, Uzbekistan 2Department of information technologies, Andijan state technical institute, Andijan, Uzbekistan 3Department of computer engineering and digital technologies, Andijan branch of Kokand University, Andijan, Uzbekistan; 2Corresponding author https://doi.org/10.5281/zenodo.17892758 Abstract. This paper presents the mechatronic design implementation for a 6 degree of freedom (6-DOF) stationary lower limb rehabilitation exoskeleton (SLLRE) robot. The proposed system features a comprehensive mechanical structure with bilateral hip, knee and ankle joints, providing enhanced rehabilitation training capabilities. The mechatronic implementation integrates mechanical design, mechatronic schemes including control, sensor, actuator systems, and safety mechanisms. The proposed SLLRE system addresses critical requirements for lower limb neurological rehabilitation including stroke recovery, spinal cord injury therapy, and gait retraining applications. Keywords: Mechatronic design, exoskeleton, lower limb rehabilitation, stationary robot, gait training. Annotatsiya. Ushbu maqolada 6 erkinlik darajasiga (6-DOF) ega bo‘lgan tayanchga mahkamlangan pastki tayanch harakati cheklangan bemorlarni reablitatsiya mexatronik loyihasi taqdim etilgan. Ishlab chiqilgan tizim chanoq-son, tizza va to’piq bo‘g‘inlaridan iborat bo’lgan murakkab mexanik tuzilishga ega bo‘lib, reabilitatsion mashg‘ulotlarni o‘tkazish uchun keng keng foydalanish imkonini beradi. Mexanik loyihalash asosan boshqaruv sxemalari, sensor va aktuatorlarni integratsiyasi, hamda xavfsizlikni ta’minlash mexanizmlarini o‘z ichiga oladi. Taklif etilgan reablitatsiya ekzoskeleti reabilitatsiyasi uchun asosiy talablarga javob beradi, jumladan insult, orqa miya jarohatlari terapiyasi va yurish qobiliyatini tiklash usullarini o‘z ichiga oladi. Kalit so‘zlar: Mexatronik loyihalash, ekzoskelet, patki tayanch hatrakat, statsionar robot, harakat mashg’ulotlari. 1. Introduction Lower limb mobility impairment is a major challenge in rehabilitation medicine, impacting millions worldwide after injuries, surgeries, and neurological events. Over the past ten years, lower limb exoskeletons have become a key technology for restoring walking and improving recovery [1]. The World Health Organization reports that over 1 billion people worldwide have disabilities, with 110–190 million needing intensive rehabilitation. Each year, about 45,000 people in developing countries and 795,000 in the United States require specialized gait rehabilitation services. Patients with limb movement disorders such as stroke, spinal cord injury, and traumatic brain injury need effective rehabilitation with reliable motion control systems. In Uzbekistan, 60% of THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 702 these patients can exercise lower limb muscles independently, while 40% rely on advanced gait exoskeletons for clinical care [2]. This highlights the need for adaptive mechatronic systems that deliver safe, personalized rehabilitation. Current exoskeletons face challenges in mechatronic structure, actuation and control. This research presents a comprehensive mechatronic design for a stationary 6 degree of freedom (6DOF) lower limb rehabilitation exoskeleton. Building on recent studies [2-8], it advances rehabilitation robotics by combining modern mechatronic principles with clinical needs. This research proposes a cost-effective, locally manufacturable 6-DOF stationary lower limb exoskeleton for spinal cord injury patients in Uzbekistan, aiming to enhance therapy, safety, adaptability, and affordability. The system includes bilateral hips, knee, and ankle joint control, integrated safety features, and advanced sensor feedback. Current research highlights the need for energy efficiency, cost savings, lighter designs, and improved human-exoskeleton collaboration to create effective, accessible rehabilitation systems for clinical and home use [1-8]. 2. Methodology of mechatronic design Developing 6-DOF stationary lower limb rehabilitation exoskeletons (SLLREs) requires understanding human-exoskeleton interaction (HEI) and integrating mechanical design, sensors, actuators, and control architecture. The complexity of lower limb biomechanics, involving seven bone types, nearly 300 muscles, and three primary joints (hip with 3 DOF, knee with 1 DOF, and ankle with 3 DOF), presents significant design challenges for achieving natural movement patterns while maintaining therapeutic effectiveness. The mechatronic design methodology adopts a systematic and integrated approach, incorporating in Fig.1. Fig. 1. Overview of mechatronic design methodology 2.1. Mechanical structure design The proposed SLLRE mechanical structure comprises six distinct frames: main, support, handle, links, foot, and control frames, shown in Fig.2. THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 703 Fig. 2. Overview of mechanical design of proposed SLLRE: 1 – mainframe; 2 – support frame; 3 – links; 4 – handle frame; 5 – foot frame; 6 – control frame The exoskeleton's mainframe is made from a sturdy metal tube or rectangle, providing key structural support, stability, and safety during training. It serves as the base for all mechanical and electronic parts, ensuring dependable performance under user weight and movement (Fig.2(1)). The support frame (Fig.2(2)) connects the device to key body areas—shoulder, lumbar, chest, and knee—to redistribute weight and reduce joint and muscle strain for people with limited mobility. Made from strong, lightweight biocompatible materials, it features supports for main body regions, body weight support systems, and tubular stands. Each side of the exoskeleton has adjustable thigh and shank segments (Fig.2(3)), fitting lengths from 350 to 450 mm. Advanced joints and actuators enable precise, efficient replication of human motion. The handle frame (Fig.2(4)) features rigid, elongated elements for effective user support. Handles on both sides improve upper body stability, posture, and safe weight transfer during rehabilitation. The foot frame (Fig.2(5)) features an anatomically shaped plate and adjustable straps to keep the user’s feet stable and prevent slippage during movement or therapy. The control frame (Fig.2(6)) is the exoskeleton's integrated subsystem for real-time command execution, monitoring, and adaptive response. It includes a monitor, actuators, sensors, and a control panel, forming the system’s operational core. The proposed SLLRE joints are designed to support hip, knee, and ankle movements. The limb is modeled with three active revolute joints, each with one degree of freedom: the hip (30° extension to 140° flexion), knee (flexes to 125°, hyperextends 5°), and ankle (20° range). Joint parameters like velocity, torque, and power are derived from gait data at 1.0 m/s, with actuator placement varying by exoskeleton design. 2.2. Sensor integration architecture The comprehensive sensor integration architecture incorporates multi-modal sensing capabilities essential for safe and effective rehabilitation training, addressing the critical requirements for precise motion control and patient safety in proposed SLLRE. Position sensing is achieved through high-precision absolute magnetic encoders with 12-bit resolution strategically positioned at each joint to provide accurate angular position feedback [10]. The safety subsystem includes emergency stop switches for both patients and therapists, adjustable range-of-motion limit switches to match individual needs, current monitoring for motor protection, and distributed vibration sensors for real-time fault detection. This integrated sensor system supports exoskeleton performance, prioritizing patient safety and effective rehabilitation. THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 704 2.3. Actuator and transmission systems Actuator and transmission system design is crucial in the proposed SLLRE, impacting precise, safe, and effective rehabilitation. The system utilizes high-performance brushless DC servo motors with advanced transmission to ensure power, precision, and safety. Each joint’s actuator is optimized: 750W Maxon EC90 motors for hip joints, 500W EC60 motors for knees, and 300W EC45 motors for ankles, matching their biomechanical requirements. All operate at 48VDC, featuring regenerative braking and thermal monitoring for efficiency and safe operation during prolonged use. Fig. 3. Actuator and transmission systems of the proposed SLLRE The transmission system uses precision harmonic drive reducers with zero-backlash for accurate rehabilitation control. Hip joints utilize 120:1 reducer for high torque, knees use 100:1 for smooth gait motion, and ankles employ 80:1 for responsive balance adjustments. The knee system is reinforced to handle heavy loads during movement. 2.4. Control architecture The low-level control implementation for the 6-DOF SLLRE employs individual joint Proportional-Integral-Derivative (PID) controllers, shown in Fig.4, specifically designed for precise position control in rehabilitation applications [10]. PID controllers represent the most widely used control technique in industrial applications due to their simplicity, robustness, and proven effectiveness in managing complex nonlinear systems such as exoskeleton robots. Fig. 4. The control architecture of 6-DOF SLLRE The proposed control architecture follows a classical feedback configuration where physical signals from the therapist interface and rehabilitation protocols generate reference position commands for each joint. The PID controller processes position error signals computed as the difference between desired joint angles and actual joint positions measured by highresolution position sensors integrated at each joint. Position feedback is provided through absolute magnetic encoders that continuously monitor joint angles, creating a closed-loop system that ensures accurate trajectory tracking essential for therapeutic effectiveness. 2.5. Safety control systems The proposed SLLRE features layered safety controls—including range, limits as well as THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 705 emergency protocols—that make it suitable for clinical use. Its advanced actuators, transmission technology, and low-level control ensure precise motion, patient safety, and adaptability, supporting effective therapy in dynamic rehabilitation settings. Emergency response features, quick motor disengagement, mechanical brakes, and thorough restart check further safeguard users. Integrated emergency buttons, limit switches, and secure patient restraints ensure comprehensive safety for clinical use. 3. Human-machine interface design The integrated control panel for proposed SLLRE represents a critical component for clinical implementation, providing therapists with comprehensive monitoring and control capabilities while ensuring intuitive operation during rehabilitation sessions. The interface design prioritizes accessibility, real-time feedback, and comprehensive documentation capabilities essential for evidence-based rehabilitation protocols in neurological recovery applications. - Display system and visualization: The display system incorporates a 15-inch high-resolution touchscreen display mounted on an articulated arm mechanism, enabling optimal positioning for therapist visibility while maintaining patient comfort during rehabilitation exercises. Real-time joint angle visualization provides continuous monitoring of patient-exoskeleton interactions, displaying bilateral joint positions, and movement trajectories in intuitive graphical formats that facilitate immediate assessment of exercise quality and patient response. - Control elements and operational interface: Control elements feature a prominently positioned emergency stop button with large, red, mushroom-head design that ensures immediate accessibility during critical situations while providing tactile identification for rapid activation without visual confirmation. Mode selection switches enable seamless transition between manual therapist-guided assistance, automatic protocol execution, and passive range of motion training, accommodating diverse rehabilitation strategies throughout different recovery phases. - Monitoring capabilities and data management: Comprehensive monitoring provides realtime graphs of limb coordination, joint synchronization during rehabilitation exercises. Range of motion tools deliver objective measurements for evaluating joint mobility and meeting insurance documentation needs. Session recording and playback allow detailed performance analysis to improve therapy based on data. Progress tracking and trend analysis enables ongoing assessment, support evidence-based modifications, and boost patient motivation with clear progress records. 4. Discussion The 6-DOF SLLRE improves on current systems with its mechatronic design for neurological recovery. It covers hip, knee and ankle movements in sagittal plane for natural walking therapy and supports bilateral stroke protocols, adjustable difficulty, and objective progress tracking. The stationary base and built-in safety features ensure suitability and protection for severely impaired users, while durable materials support reliability. Cost-effective design and modular components streamline manufacturing and maintenance, enhancing accessibility. An intuitive interface fits into clinical workflows and supports electronic health record compatibility. The platform is ready for future upgrades like machine learning, Virtual Reality, and physiological monitoring, keeping it innovative and clinically viable. THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 706 5. Conclusions This paper details the development of a sophisticated mechatronic design for 6-DOF SLLRE intended to meet pressing needs in neurological rehabilitation. The integrated approach effectively merges mechanical engineering with cutting-edge sensors, actuators and control systems, resulting in a rehabilitation device that is safe, efficient, and suitable for clinical use. The proposed SLLRE system meets the increasing need for intensive, measurable, and secure rehabilitation methods. Its stationary design achieves a strong balance between therapy potential and safety, making it ideal for use in clinics, hospitals, and specialist therapy centers. Thanks to its 6-DOF design, the device supports extensive lower limb training, including bilateral exercises essential for stroke and neurological recovery. This holistic mechatronic integration ensures high performance throughout the system while maintaining adaptability for various user groups and treatment plans. Future efforts will focus on clinical validation and refining control algorithms to further improve the system’s therapeutic value and versatility in healthcare settings. This foundational work sets the stage for continued innovation in rehabilitation robotics and neurological therapy technologies. Acknowledgements The support and assistance of partners from Rehabilitation center in Andijan, Uzbekistan for the work done is gratefully acknowledged. Author contributions All authors contributed to the study conception and design. Material preparation, data collection and visualization were performed by Javlonbek Rakhmatillaev, Nodirbek Kimsanboev, and Umidjon Takabaev. The first draft of the manuscript was written by Javlonbek Rakhmatillaev and all authors commented on previous versions of the manuscript. All authors read and approved of the final manuscript. Conflict of interest The authors declare that they have no conflict of interest. REFERENCES 1. 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