**5. Control technique**

Computational Intelligence in Electromyography Analysis – 442 A Perspective on Current Applications and Future Challenges

reasons mentioned for a 2nd order high pass filter.

*4.1.3. Band pass filtering for EMG* 

**Figure 20.** Band Pass Filter Response

**4.2. Amplification** 

them in series.

*f1* should be 65-70 Hz and *f2* be 150-180 Hz.

of a non-inverting amplifier, shown in Figure 21.

and in the case of band pass filter, it is between *f1* and *f2.* 

pass filter response is shown in Figure 20.

A 2nd order low pass filter is again recommended as compared to a 1st order one for the same

As mentioned previously, for the transmission of pure EMG, the high and low frequency noise should be deleted. For this purpose, only a specific band of frequency should be carried forward [20]. This can be made possible with the help of a band pass filter. A band

The frequency region where the response of the EMG signal is '1' is called the 'passband'

A band pass filter can be designed by connecting a low pass and a high pass filter in series. By selecting proper values of R and C, we can develop a band pass filter which can carry forward the most effective component of the EMG signal. It is recommended that for EMG,

After the signal has been filtered properly and a suitable band of EMG frequency is obtained, the next stage is amplification. The EMG signal obtained has to be powered up to a suitable level. The amplification of the EMG signal can be easily carried out with the help

The gain of the amplifier is provided in the figure as 'Av'. The non-inverting amplifier is only used when the signal is being received from a single wire referenced to ground. Amplification can be done in stages in order to cater for chip requirements, by cascading In order to successfully achieve robotic prosthesis, an effective control technique is very important in order to drive the electric motors in the mechanism. With the advent of modern microcontroller technology, the control options available today have never been so effective.

For implementing the desired control to the motors, the amplified EMG signal in analog form has to be converted into digital format. After this, the motors are driven with the help of a microcontroller through the thresholding technique. These techniques will be discussed in detail in this section.

### **5.1. Analog to digital conversion**

The digitization process of the analog signal is carried out with an Analog to Digital Converter (ADC). Nowadays, the ADC has become a common component of modern electronic devices. Their use has become highly varied and widespread. Before using the ADC, its specifications, advantages and limitations have to be analyzed in order to select the most appropriate one for the application. In the same way, important considerations have to be taken into account while converting EMG signals into digital format.

Control of the motor will be developed after the EMG signal is converted into digital format. A particular ADC has a specific range of conversion i.e. there are maximum and minimum levels defined for an ADC over which it can operate. An ADC can convert the analog signal over a certain number of bits. The number of bits which an ADC can convert is known as its "quantization scheme". If an ADC has a defined range and a quantization scheme of *'n-bits'*, then the resolution of the ADC can be given as:-

$$\mathbf{V}\_{\text{resolution}} \equiv \mathbf{V}\_{\text{range}} / (\mathfrak{D})^n \tag{6}$$

Signal Acquisition Using Surface EMG and Circuit Design Considerations for Robotic Prosthesis 445

**Figure 22.** Block diagram indicating all steps for driving a robotic mechanism

them, allowing us to classify different motions of the hand [22].

of the whole circuitry can be reduced up to 95%.

set for their control [21].

As an example, we discuss the control of a robotic hand. There are two primary motions of the human hand, flexing and extending. For flexion, electrode should be placed on Flexor Digitorum Profundus and for extension; the electrode should be placed on Extensor Digitorum Communis [21]. As both muscles exhibit different signal patterns, therefore, a multi-channel input scheme should be employed, so that both signals are gathered independently. Both signals should be observed carefully and a suitable threshold should be set after filtering and amplification. The same procedure is to be followed in order to develop control of all the fingers of the robotic hand i.e. by placing EMG electrodes on specific muscles which control

The signal observed from a subject with a moderate built is shown in Table 1. The amplification set for the detected EMG signals from the subject was 10,000. Table 1 provides the EMG signal response from each of the subject's fingers after amplification and threshold

Size is a very important factor while designing an electronics circuit. A circuit occupying minimum space will be most appropriate in application. A size effective circuit will be easy to place and handle in a robotic mechanism. Advances in biomedical instrumentation have brought fruitful gains to robotic prosthetic technology. The ADS1298 is a 64 pin IC with 8 differential inputs with programmable gain amplifiers (PGAs) and a 24 bit ADC. The PGAs can provide a maximum gain of 12 but the 24 bit ADC quantization scheme is enough to process the EMG signal [23]. With all necessary peripherals attached to a single IC, the size

Latest robotic researches have enabled us to design and create multi-degree of freedom robotic mechanisms [24]. A good mechanical design and apparatus is essential for efficient robotic prosthesis. Newer electronic components and materials have made robotic prosthesis more functional and adaptable. When we talk about materials, the perfect one should be lighter, durable, adjustable and comfortable for the user. Nowadays, carbon fiber frames are being employed as a solution to this matter. An example of a carbon fiber limb is the state of the art Ottoblock C-Leg. The C-Leg has a built in computer which analyzes data

from various sensors and actuates the knee using a hydraulic cylinder.

While converting an EMG signal into digital format, three specifications should be taken into account. 1) Quantization, 2) Range of conversion and 3) Sampling rate [21].

The number of bits, which an analog signal can be converted into digital format by an ADC, is known as quantization. The maximum amount of voltage an ADC can convert into digital quantized bits defines the range of an ADC. The sampling rate means the number of samples an ADC can convert in one second.

After the EMG signal has been amplified up to a suitable level, the range of an ADC should be selected so that it can comprehend a particular voltage level. The number of quantization bits is important, as they determine the resolution of the ADC. The more the number of quantization bits, the less will be resolution of the ADC; the more it will help in control purposes. The ADC sampling rate is also a key consideration. It should be kept as large as possible so that the data loss of EMG is kept at a minimum [21].

ADCs are now available as a peripheral with microcontroller chips and can give sampling rates greater than 1000 kSPS and quantization schemes of more than 24 bits.
