UPPER LIMB EXOSKELETONS

UPPER LIMB EXOSKELETONS

1. Desing of the upper limb exoskeletons.

   • Purposes
     • Power amplification.
     • Assistance.
     • substitucion of the motor function.
     • Replicate the kinematics and dynamics of human.
     • The design deped from the end user application.
     • Complex skeletal structures.
   • Classification.
     • Degrees of Freedom.
       • Single joint.
       • Multi joint.
     • Type of actuation.
       • Electrical.
       • Pneumatic.
       • Hydraulic.
       • Shape memory alloys.
       • Passive.
     • Joints.
       • Shoulder.
       • Elbow
       • Wrist.
       • Hand.
     • Applications.
       • Used in rehabilitation
         • Reduces the need of a therapist.
         • Reduces the period of rehabilitation process.
         • controlable and safe.
       • Used for power assist
         • Portable and advantage of mobility.
         • Compact, ligh weighted, easy to use and setup.
   • Control Strategies
     • Assistance.
       • The robot is supporting the weight of the limb damaged and providing strength to finish the task.
         • Passive control.
           • The easiest way to control an exoskeleton is to control its motion rigidly along a certain reference trajectory with the help of position feedback control.
           • Passive trajectory tracking.
             • These references are regulary made by recording the therapist contributions regarding the subject limb joined to the exoskeleton amid a teaching stage.
           • Passive mirroring.
             • Can be used for the exoskeletos that are intended to support both human arms simultaneosly. it involves the synchronous passive mimicking of the movement and behavior of a healthy limb. it is employed in a master and slave configuration.
         • Partially Assistive Control.
           • Impedance/admittance control.
             • Real-time adaptability between the robotic exoskeleton and contact forces is resquiered to improve the interaction between two bodies.
             • Imdance control is a model based force controller with position feedback.
             • This techniques is widely used in robotic exoskeletons to improve the pHRI and it has been observed that this method is quite effective in the case of lightweight
     • Correction.
       • In the rehabilitacion scenario in which the robot acts only when the patient performs incorrect movements.
         • Tunneling
           • Comprises making virtual channeles for the end-effector or the joints of the exoskeleton in which the subject movec:once he/she leaves the channels, the input control takes them again into the channel as though a spring impedance as connected from the lim to the focal point of the virtual channel.
     • Resistance.
       • Is that the robots restricts movement. it increases the complexity of the task so that the patient learns and improves his ability to correct movement errors.

2. Possible challenges in Upper Limb exoskeleton development.

   • Discomfort and misalignment.
   • Human-robot interaction
   • Kinematic compatibility.
   • Workspace limitation
   • Singularity problem of mechanical system.
   • Sensing and estimation.

3. Examples

   • LOKOMAT16
     • Is a robot gait orthosis combined with a harness supported body weiight system, used in combination with a treadmil.
       • The patient´s leg joints are guided according to a preprogrammed gait kinematic pattern.
   • Gait Trainer
     • Is based on a double crank and rocker gear system.
       • Cosists of two footplates positioned on two bars, two rockers and two cranks which provide the propulsion.
   • G-EO System
     • Is based on the end-effector principle and was desing to minimoze the therapeutic effort needed for relearning walking and also stair climbing.
       • the trajectories of the footplates as well as the vertical and horizontal movements of the center of mass are fully programmable.
   • EXO-SPINE
     • Have been developed to support and strengthen the user´s apine and can aso be one of the rehabilitation device too.

4. Actuation

   • Electric motors.
     • High control precision and quick response. focuses more on how to arcchive a better physical human machine interaction high cost.
   • Series elastic actuators.
     • Archiving stable force control.
   • Hydraulic actuators.
     • Challenges to the controller´s design. heabypumps and compressed gas containers may sacrifice the system´s portability.
   • Pneumatic actuators
     • control is less precise. additional this category of actuatos suitable providing assistance or robotic physical therapy to elderly people and patient.

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