2 DOF Upper Limb Exoskeleton Trainer for Elderly People Jere Lethtinen Nimish Bhatt Niko Räsänen Samu Salerto Tuomas Tervamäki

Arm exercises Most of you must be familiar with these exercise machines. Our topic of presentation is related to exercise and muscle strength.

Muscle Rehabilitation Aim Effects/Causes Muscle Degeneration Range of motion Ageing Effects Sedentary Lifestyle Muscle Rehabilitation Explain: Muscle degeneration It is accelerated by ageing as you grow older and sedentarty life style i.e. lack of physical activity. These effects also lead to reduced range of motion Hence muscle rehabilitation is needed especially in aged population.

Exoskeleton :Why? Range of motion (ROM) Adjustable to user Portability Suitable for elderly people Complete range of motion helps restore lost range of motion. Suitable for users varying in age and sex. Portability allows it to be transported to disabled patients in remote places. It could be designed to suit elderly people.

Muscle contraction: Isokinetic Constant velocity movement Varying resistance Maximal loading throughout entire ROM Safest form of exercise Max. Torque: There are various muscle contractions like isotonic, isometric and isokinetic. Isokinetic exercise consists of, Constant velocity movement of limbs accompanied by, Varying resistance such that, The muscles are loaded maximally throughout the ROM. Varying resistance ensures that the resistance doesn’t exceed muscle strength hence making it the safest form of exercise. From research studies, we found torque values of… for shoulder and … for elbow. Shoulder Elbow ~14Nm1 ~10Nm1 1 Danneskiold‐Samsøe, Bente, et al. "Isokinetic and isometric muscle strength in a healthy population with special reference to age and gender." Acta physiologica 197.s673 (2009): 1-68.

Constant velocity & Torque measurement Resistance Mechanical Links Lets consider the elbow flexion movement. The Exoskeleton would consist of mechanical links connected, at joints to create resistance to the motion, Such that velocity stays constant, Which would require velocity measurement and finally torque measurement to evaluate muscle performance. Constant velocity & Torque measurement Resistance

Components & Materials D.C. geared motors (8Nm): Resistance Rotary encoders: Velocity measurement Teensy ++2.0 microcontroller: PID Control Current Sensors: Torque measurement Aluminium: Lightweight frame We considered pneumatic, hydraulic and electric actuators, and realised that electric would be the easiest to control but at the same time would be heavier compared to pneumatic. Motors were coupled to rotary optical encoders for velocity measurement. Teensy is Arduino based microcontroller with a smaller form factor and had enough output pins to serve our purpose. Current sensors to measure motor current and derive motor torque.

Prototype: 2 DOFs Exoskeleton Motor: Shoulder joint Adjustable Frame: Aluminium Electronics: Control system The frame is strapped using a vest to the body. Both the motors are connected to rotary optical encoders. Electronics includes microcontroller, motor driver, current sensors and bluetooth serial for sending torque and velocity data. It is powered by and external power supply. The mechanical movements of device are limited to range of motion so that it doesn’t cause injury. There is a kill switch which cuts off the mail power to the device as safety is case of malfunction. Motor: Elbow joint

Operation flow chart The PID algorithm implemented in the microcontroller has a set reference velocity. When a user applies force, causing movement and rotation of dc motors, the microcontroller detects the movement and also calculates the velocity from encoder, and in turn generated a PWM to drive the motor such that the velocity stays constant. Once user stops moving his/her arm, the microcontroller switches off the motors. Both elbow and shoulder motors operate independently on the same flow chart.

Scope for improvements Weight Ergonomics Mechanical Electronics

Conclusions Positive user feedback Proof of concept Foundation for further development