Experimenting with Transmitting EMG Signals to 3D Printed Myoelectric Prosthetic Hands

Amputees have some choices when it comes to 3D printed prosthetic hands, in regards to whether the artificial limb is operated by mechanics or neurological signals. We’re also seeing examples of 3D printed myoelectric prosthetic hands, which is an externally powered artificial limb controlled by the electrical signals that are naturally generated by our muscles.

A group of researchers from the Gujarat Institute of Technology and Government Engineering College, which are both in India, recently published a paper, titled “Wireless Transmission of Electromyography (EMG) Signals to operate 3D Printed Myo-Electric Hand,” that explains their new methodology of wirelessly transmitting Electromyography (EMG) signals to a 3D printed myoelectric prosthetic hand.

The abstract reads, “Sometimes in case of particular amputees, fetching EMG signals by sensors is not possible from that destructed muscles but, EMG generated from healthy muscles besides that amputees can be used in the transmission of signals. The objective of this research is to generate the new technique for transmitting EMG signals without wire from any adequate healthy muscles. In this methodology, we used the EMG sensor to detect EMG signals, which perform a pre-processing task and featured extraction on EMG signals by using a microcontroller. That extracted output then applied to universal remote control transmitting circuit as input which sends the signals to the receiver circuit, output signals from that receiver circuit directly applied to servo motor of a myoelectric prosthetic hand. The objective of this research to fetch and carry EMG signals from the healthy muscle and train the victim suffering from amputee in which acquiring adequate EMG signal from very adjacent tissue of damaged area is not possible due to burning and inflammatory issues.”

The researchers wrote that myoelectric hands are more reliably and accurate, and that amputees can configure the motion of the hands in a much more natural way, with more freedom. EMG-based myoelectric hands are popular on the market, because they are more efficient. You can see how the team’s 3D printed myoelectric prosthetic hand, which is controlled through wireless EMG transmissions, works in the diagram below.

Block Diagram of Wireless EMG Control for Prosthetic Hand

The team conducted their experiments on the right hands of six people, ages 21-24, that were not differently-abled, and two with below the elbow amputations. Because the subjects all had major differences in body muscle fat, the results of electrical signal powering the prosthetic were altered a little more than normal.

EMG signals are associated with the muscle’s contraction and relaxation movements, but the body’s signals are of low potential, so amplifier circuits and filters are needed to help get rid of unnecessary noises. Traditional EMG analysis instruments often use painful needle electrodes, but wireless EMG ideology can help in situations where it’s not possible to get adequate signals across the muscles for various reasons, such as muscle fatigue and allergic reactions. In this experiment, a microcontroller with an embedded 8 bit ADC (Analog to Digital Converter) was used to sample the signal, while a motor driver circuit controlled the amount of voltage and current supplied to drive the motor.

“There are many modules and terminology that are available in market like Bluetooth and Wi-Fi connectivity. But the most significant concern undertaken by our study that all modules requires basic power consumption and first time pairing and in such case that doesn’t proved to be most useful due to some connectivity issue. Therefore, developing RF Based Wireless unit opted by our team,” the researchers wrote. “Since we had utilize almost 5 servo motors, we need to develop multichannel wireless TX that can control up to 5 different appliance or motor. Wireless TX concept is based on transmitting our low frequency signal from one end to another by modulating with predecided carrier frequency which has high frequency which can transmit signal at a large range, even prosthetics don’t require such a high range. We had used 27MHz of frequency to modulate our low energy signal which is encoded to certain signal by IC TX-2B.”

Wireless vs wired prosthetic hand

The team noted that by 3D printing the hands, there are more opportunities to design accurate parts for good results. They used a Makerbot 3D printer to make the hands out of ABS and PLA, with 90 to 100% infill and normal print speed. Supports were used, and the hands were polished for a better overall aesthetic. Each hand had metacarpal fingers and an enclosure, wrist, and ring of the wrist, along with a standard below elbow piece to enclose and link the structure so the fingers could be moved.

In order to learn more about the participants’ muscles and find out which ones generated the signal most dominantly, an EMG spectrum analysis was performed on each person before muscle sensors were deployed on their arms. This would allow them to avoid inconsistent signals.

One of the amputees could not generate an EMG signal from his lower elbow, possibly due to muscle destruction or a lack of physiotherapy exercise.

Motor Moving Mechanism of the Prosthetic finger

“Wireless EMG Based Prosthetic Hand can be consider meaningful for both condition either person suffering with wrist disarticulation or standard above elbow,” the researchers concluded.

“Wireless method completely isolates the sensor and actuator portion because they get communicate by radio frequency network only which drives by low power.

“Overall, we had taken observation that it is novel technology to transfer EMG signal from healthy muscles rather than amputate hand to the sensor to operate prosthetic hand.”

Co-authors of the paper are Sunny M. Patel, Dinesh R. Damodar, Chintan A. Patel, and Raj B. Patel.