Sensing and Processing of Bio-metric Signals for use in Low Cost Bio-robotic Systems

What is Bio-Metrics? Biometry − Bio (Greek word for Life)+ Metrics (Measurements) Biometrics is the science of measuring and analyzing biological

data. Biometrics refers to technologies that measure and analyze

human body characteristics such as DNA, fingerprints, eye retinas and irises, voice patterns, facial patterns and hand measurements.

How Bio-Metrics work?

• Input Interface (Sensors)- It is the sensing component of a biometrics system that converts human biological data into digital form.

• Processing Unit- microprocessor, Digital Signal Processor (DSP), or computer that processes the data captured from the sensors.

• Database Store- The database stores the enrolled sample.

• Output Interface- The output interface communicates the decision of the biometric system to perform a task.

Need for Bio-Robotic Systems?

• To replace Humans in Hazardous Working Conditions.

• Recovery of Human Organ Functions.• To perform high Precision tasks ,such as

Surgeries.• As Exoskeletons for paralyzed people.

Prosthetics

• Prosthetics are artificial devices that replace injured or diseased body parts

• There are two types of Prosthetics- 1. Passive Prosthetics 2. Active Prosthetics

Requirements of a good Prosthetic

• Should match the real Limb as close as possible

• Same Size as the Limb• Low Weight• Economical• Long Lasting

Existing Prosthetics

1. Passive Prosthetics: They do not have sensors or any control mechanisms. They are cheap.

2. Active Prosthetics: They use sensors and Control mechanisms to mimic the actions of the real limb. They are far more expensive than Passive Prosthetics.

Sensing Technologies1. Electromyography(EMG): Electromyography (EMG) is a technique for evaluating and

recording the electrical activity produced by skeletal muscles. An EMG signal is the electrical activity of a muscle’s motor units Most commonly used control method for Bio robotic systems

(Prosthetics) EMG frequency spectrum falls in the 0-500Hz range

2. Electroencephalography(EEG): An electroencephalogram (EEG) is a technique used to track

and record electrical activity of the brain. EEG measures voltage fluctuations resulting from ionic current

within the neurons of the brain.

Invasive Vs Non-Invasive1. Invasive – Requires Surgery or Implantation Risk of Infection or Electrode rejection High resolution of the obtained Signals More Expensive Used in special cases

2. Non-Invasive- Doesn’t require Surgery or Implantation Low resolution of the obtained Signals Less Expensive Commonly used

Choice of Sensing Technology

Advantages of EMG:• Low cost• Simplicity: Most times, surface electrodes are

sufficient to collect adequate data.• Prediction: In most muscles, the EMG activity

precedes the motion of the actuated limb.

Circuit Design

• Sensing Circuit Comprises of 3 stages1. Input Amplification2. Filtering3. MAV(Mean Average Voltage) Circuit

Input stage

• Consists of Sensory Circuits• Sensory Circuits comprises of a set of Silver

Chloride Electrodes attached to person’s skin• One electrode is placed at core of the target

muscle• Other electrode is placed at a remote location• An instrumentation amplifier is used to

amplify signal by x1000

Filtering Stage

• Filtering stage consists of High Pass and a Low Pass Filter

• More Dominant frequencies are identified after Fourier analysis and rest are filtered out

• Frequencies 20Hz to 400 Hz are allowed to pass

MAV Circuit

• MAV (Mean Average value) circuit consists of1. Peak Detector2. Clipping Circuit3. Integrator• Peak detector converts signal to a series of

Peak spikes• Then Peak values are cut off at a safe Voltage

level

• Integrator provides a slow signal that rise and fall with the amount of muscles activity.

Conclusion

• Prosthetics based on EMG offers an effective low cost solution for amputees.

• Prosthetics based on EMG have the following disadvantages:1. Injuries are not same for every amputee, so

Prosthetics have to be customized.2. EMG signal strength depends on many factors,

such as Muscle size ,Skin type etc, some of which may vary with time.

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