1 Design of a Cost effective EMG driven Bionic Leg Tahmid Latif, Choudhury Mahboob Ellahi, K Siddique-e-Rabbani 1 , Tanveer Ahmed Choudhury Department of Electrical and Electronic Engineering Islamic University of Technology (IUT), Gazipur, Bangladesh 1. Visiting Professor. Base affiliation: Department of Physics, University of Dhaka, Dhaka, Bangladesh tahmidlatif@yahoo.com, mahboob.ellahi@gmail.com, srabbani@agni.com, tanveerchoudhury@yahoo.com Abstract Conventional low cost leg prosthesis is essentially a fixed passive structure which makes walking possible with some difficulty, and climbing stairs is extremely difficult. The present work was taken up to design a low cost bionic leg prosthesis which will have an active (battery powered) limited rotational movement of the knee joint, controlled by voluntary EMG (electromyogram) signals from two opposing muscles from the thigh, one to rotate the leg backwards (flexion) and the other forwards (extension). The goal is to provide amputees with improved leg prostheses at low cost. EMG signal was acquired and processed to control a dc servo motor operating the knee joint using a microcontroller. The designed prosthesis will allow a user not only to walk with a better gait, but also to climb stairs with ease. The EMG signal was amplified and processed to give an output only when it crossed a certain amplitude threshold. A microcontroller was used to sense the presence of this output which was programmed to decide whether to activate the motor or not, and if yes, in which direction to turn it. The design involved developing the necessary EMG and processing circuitry, interfacing the output to the Microcontroller, developing the driving circuitry for bidirectional rotation of the motor, and programming the microcontroller. During the course of the present work it was possible to control the rotation of a motor using a simulated EMG signal. Keywords: EMG, Prosthesis, Amplifier, Data Acquisition, Microcontroller, Worm Gear 1 Introduction The human leg is a complex and flawless part of the body. Consisting of a number of complex functions and providing multiple degrees of freedom, the human leg is almost impossible to imitate by any means of prostheses. Commercially available simple leg prosthesis has zero degree of freedom or in some cases just one. The latter provides a passive knee joint, which cannot be utilised to its best due to lack of voluntary involvement. These do not prove to be user-friendly and the weight turns out to be a major problem. While walking, the user has to pull the leg along and climb stairs in a similar way; control requires a lot of energy that easily fatigues the user. The main aim of this work was to design and then fabricate a prosthetic leg with a motor operated active knee joint (hence the term bionic leg), being operated by voluntary control of the user through electrical signals (EMG) from thigh muscles. In short, the bionic prosthesis will:  provide voluntary of dc motorized knee joint  improve gait (manner of moving)  allow stair climbing with ease  eliminate undesired movement at knee Although recent developments in the west have produced very sophisticated bionic legs with many advanced features, these will remain out of bounds for most of the Third World because of ‘cost’. The designed bionic leg focuses on cost-effectiveness and quality as well as comfort and ease of use. 2 Electromyogram Whenever a physically fit person is walking or an amputee is walking, using a passive prosthesis or crutch, their muscles generate signals due to movement of his/her thighs that corresponds to movement during walking. These signals are EMG (Figure 2.1), pictorial representation of electrical activity of the contracting muscle. Voluntary EMG results from voluntary contraction of muscles, under wilful action of the brain. Evoked EMG results from artificial stimulation of muscles. Voluntary EMG from thigh muscles will be used for rotation of motor at knee. To make things simpler and to use a non-invasive technique, the signal is sensed using surface electrodes, placed over the desired muscle. Use of needle electrodes will make the use of the prosthesis, with needles pierced in the skin, a painful experience, which is not a practical proposition. 3 Designed System As shown in the block diagram of the designed system (Figure 3.1), signals from thigh muscles, extracted using skin surface electrodes, are amplified by EMG Amplifier units followed by Signal Conditioning units. Since the amplitude of the muscle signals are very small (~ 1 mV), t Figure 2.1 Typical EMG Signal Motor Driving Unit Microcontroller ADC MUX Sensor EMG Amp Signal Conditioning Unit Flexor Unit (muscle signal) (muscle signal) Extensor Unit EMG Amp Signal Conditioning Unit Figure 3.1 Block Diagram of Designed System