Bio-Signal Processing: How It Works

Developments in prostheses are offering users more functionality and agility than ever before. The use of bio-signal processing, in particular, has transformed how prostheses work in correlation with a user’s body. Bio-signal processing allows users to control their bionic arm in a manner similar to how they controlled the arm lost through amputation. 

As a result, the new arm serves as a fully functional extension of the user’s body as opposed to a mere accessory. For users interested in learning exactly how bio-signal processing works within a bionic arm, continue reading. 



To start, we’ll go over some background as to how bio-signal processing came to be. In the past, the only available prostheses had very simple hand open and close functions. The problem with this was that the prosthetic arm was designed to substitute the sound-side hand but these prosthetic hands ended up having far fewer degrees of freedom.

Additionally, most tasks performed by the prosthesis were awkward as controls for the prosthesis weren’t related to the actions of a normal limb. For example, the elbow movement of a prosthetic arm would result from the amputee’s shoulder, whereas a normal elbow would be able to move independently of the shoulder.

Having recognized these problems, prosthetic centers began looking for a new solution. Upon research, it was observed that the biological signals that controlled bodily actions, which had been thought to be lost in amputation, were still present in the body of the amputee. 

These signals could be used to control a prosthesis instead of using gross body motions like in traditional prosthetic limbs, such as body-powered prostheses. As such, the amputee’s ability to control the device would exceed their ability to control a conventional prosthesis. The primary advantage of this would be that the prosthesis' mode of control would be similar to that of the corresponding amputated limb, and more intuitive. 


Use of Nerve Signals


Upon this realization, it was discovered that the use of nerve signals for control purposes could offer considerably improved rehabilitation in parallel with the use of muscle signals. Nerve signals facilitate the voluntary and involuntary activities in the performance of bodily functions, including receiving physical sensations. By utilizing the residual nerves in the arm, which contains both sensory and motor nerve fibers, amputees could control their prosthetic arm. 

So, how does the connection work? Studies found that electromyographic signals (EMG) were the most practical bioelectric signal for control purposes. These electric signals could be generated by the contraction of muscles in the patient's residual limb. 

The simplest method of observing EMG signals in the body would be to place any pair of electrodes on the surface of the skin over a muscle. Once the electrode is taped in place, it will look for signals resembling the output of a noise generator and increase and decrease in correspondence with any muscle tension. As a result, the control behavior in the prosthetic arm would be similar to that of a normal arm. 

That being said, the placement of the electrodes and their ability to observe EMG signals is dependent on the anatomy of the amputee. The ability to be able to utilize EMG signals is important for the use of a myoelectric device, as these signals operate the hand.  Thankfully, even with very weak signals operation of a bionic hand is still possible.  During the patient evaluation with the prosthetist, these EMG sites will be tested


The Bionic Arm


The bionic arm was designed to produce a prosthesis suitable for EMG control, one that could be fitted to the amputee in order to operate with enhanced control. When the bionic hand comes into contact with the amputee’s skin, the electrodes can receive signals from the user’s underlying muscles. Once connected, the hand will begin to function according to the user’s control. 

In tandem with the electrodes and EMG signals, the hand will also require a motor control portion of the program. Essentially, the program will sample the signals through a processing loop and compute the difference between that signal and the result of the EMG signal. These signals will then be processed and transmit the result back out of the computer to the motor. 

With the bionic arm fitted to the patient and properly programmed, the user can begin to effortlessly control their arm. As the arm is controlled using signals, it will move as close to a normal arm as possible, with greater control and dexterity than other traditional prosthetics. Furthermore, with a high-functioning arm, users can even control the movement of individual fingers, providing them with greater control and functionality. 


How We Use Bio-Signal Processing


Our own product, the Zeus, is a high-functioning, multi-articulating bionic hand controlled by bio-signal processes. Advanced signal processing and wireless gain adjustment in our EMG sensors, paired with proportional speed, allow for a seamless transition between precise yet strong grips. 

Once fitted to the arm, users can easily control the device, which will collect signals for optimal control. This, paired with our highly advanced software, allows users to customize individual finger grips to their unique needs. With the Zeus, users achieve greater control and strength than alternative prostheses, providing them a similar level of functionality to that of a normal hand.  

If you’re interested in learning more about the Zeus and how it works, visit our website or schedule a free consultation

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