Cost Effective Electrically Powered Wrist-Hand Automated Orthotic Exoskeleton

According to world stroke foundation 1 in 6 people worldwide will have a stroke in their lifetime?. One of the group member?s Grandmother have had multiple strokes which resulted in right hemiplegia. She started physiotherapy post stroke very enthusiastically to get better and resume the kind of lif

Project Title

Cost Effective Electrically Powered Wrist-Hand Automated Orthotic Exoskeleton

Project Area of Specialization

Biomedical Engineering

Project Summary

According to world stroke foundation 1 in 6 people worldwide will have a stroke in their lifetime”. One of the group member’s Grandmother have had multiple strokes which resulted in right hemiplegia. She started physiotherapy post stroke very enthusiastically to get better and resume the kind of lifestyle she had. But, with time her motivation declined to none because no matter how hard she worked the improvement was very small and she was still very dependent on others for her basic daily life needs such as eating and drinking. This is the case with so many more post stroke patients. Hemiplegia (sometimes called hemiparesis) is a condition, caused by a brain injury that results in a varying degree of weakness, stiffness (spasticity) and lack of control in one side of the body. Stroke is a very common brain injury that results in this condition. Rehabilitation after stroke is very important for full recovery of control but it is a slow and tedious process. Post stroke patients suffer from depression which has negative effects on functional recovery. They lose hope that they’ll get better. The final deliverable of this project is a product that gives the patient a sense of achievement, independency and boost of hope. While, improving their physical health and bringing back muscle control.

The complete product of this project is planned to aid improvement for hand movements (better grips) for stoke patients (not limited to). This design uses EMG signals from the radial and ulnar muscles from the hand and actuates the fingers according to the impulses (EMG signals). Hence, aiding the muscle by amplifying the movement of fingers through mechanical actuation. It is an exoskeleton which is a wearable, protable, aesthetic product. It is in short a novel,cost effective product.

Project Objectives

In an interview with a physiotherapist at Aga Khan University Hospital, she explained how difficult and challenging stroke recovery can be both physically and mentally. She further explained to us that the process to recovery needs to start right after the operation. It starts by helping the patient be able to sit, stand and lie down on their own after which they can be discharged from the hospital. After that, patients continue rehabilitation at home and visits at the  physiotherapy department.

She mentioned that on average a patient needs to come in for 2 hours/day till at least 6 months (can vary from severity of the stroke). During these sessions basic physiotherapy is given to increase muscle movements and make new neural pathways in the brain. After some recovery in walking and arm movements, the patient starts occupational therapy which focuses on wrist-hand movements. She mentioned that wrist hand movements require concentration and precision, they are the latest to recover. Wrist-hand movements are a necessity for very basic real-life tasks such as eating, drinking, writing, etc. This was further reimbursed by a stroke patient herself (the group member’s grandmother). According to her and her family members, the most challenging tasks of recovery were speech and hand/finger movements. Her finger movements have still not completely recovered even after 5 years because she lost hope in between her therapy.

To tackle this problem, the project’s aim is to come up with a way to perform continuous physiotherapy while doing every day to task to keep the patient motivated. A lot of methods have been under research and being applied in this field. The existing technologies are as follows:

• Passive orthotic devices are being used in hospitals and homes as exercising tools for the hand.
• Active devices are also being used in different ways such as Contra-laterally controlled functional electrical stimulation (CCFES) system. The patient controls stimulation to their paretic hand with an instrumented glove
  worn on the strong hand, Robotic replacement of mirror hand therapy. 

The process is shown in the diagram below.

Final objectives of the project are as follows:

• Adding automated thumb movements by improving the existing design,
• Minimizing cost as compared to available solution,
• Fully Automated, portable and comfortable product

The project aims to get at least two degrees of freedom for the thumb through automatic actuation. After going through the literature, we concluded that the movement of fingers were possible through the radial and ulnar muscles, but the two degree freedom of the thumb is particularly difficult to implement, and the project is targeted towards solving this problem for defined number of grips.
 

Project Implementation Method

The first step is to make a prototype of the product. The prototype consists of:

1. Acquistion of signals: By using off the shelf module and Designing a module. 
    
2. Control of one type of grip: Power grip was chosen as it is a low precision movement. It uses the bulk muscle of the hand for force generation rather than the strength of individual fingers.

3. Extending Control to individual movements: More degree of freedom and different types of grips and two DOF for thumb movements.

4. Select a design:  Servos were chosen over linear actuators as servos are lighter in weight. 

Once the prototype is ready we will move forward to the designing and including all four grips:

1. Power Grip

2. Spherical Grip

3. Lateral Grip

4. Pinch Grip

Making it precise and with less fluctuation. 

Finally we will 3D print the following design and assemble it.

Benefits of the Project

The idea of the project mainly focuses on the advantage it will give to stroke patients and the society overall. Stroke recovery is a time taking process which causes patient to lose the will to recover as they are dependent on others for basic life tasks. Our project will give them the independence to perform the basic task hence giving them the motivation to work hard for recovery.

Moreover, one of our main aim was to make this project cost effective. According to our interview in Aga Khan we came across similar equipment that costs around 50-60 lac and that too were imported from abroad. Therefore, making it difficult for patients to benefit from it.

Hence, it was decided to come up with the idea to replace this with a “Cost effective" equipment that patients can use in daily life. But this had to be ensured along with the working of the product. It should fulfill its purpose while being portable and user friendly.

Technical Details of Final Deliverable

The Design for the thumb is a little complex and was inspired by an orthotic device for stroke recovery which used electrical actuators to push the fingers inward. The final design for the thumb movements uses electrical actuator coupled with a servo for two-dimensional movement of the thumb. The thumb has four primary movements. For the extension and flexion an electrical actuator will be used that will be placed on the back of the thumb to push it forward and inward. For adduction and abduction, a servo/pulley system (pulley located at the end of the index finger) will be used to pull it away from the palm and towards the arm.

For the four fingers, the plan is to simply use servos placed on the wrist attached to the fingers via threads used to pull the fingers for different grips. A total of 3 servos are being used here: One for the index finger, one for the middle finger, and one for the ring and pinky finger combined.

Placement of the sensors:

• For fingers, two electrodes will be placed on the radial and two electrodes will be placed on the ulnar muscles and one on a bony part of the arm.
• For the thumb the electrode will be placed on flexor and abductor muscles. 

Module consists of:

1. SIGNAL ACQUISITION: In this phase our main agenda is to read the signal from the muscles through the electrodes attached (position of electrodes shown in figure 4). This is done by using a differential amplifier with a gain of 110. This amplifier will both read and amplify the signal.
2. SIGNAL CONDITIONING: This phase consists of a pre-amplification stage followed by AC coupling and a high pass filter. The pre-amplification stage dwells with an inverting amplifier with gain 15. Inverting amplifier helps prevent oscillation plus instability and gives the flexibility of adding any valued resistor and capacitor. Following pre amplification, we have an AC coupling circuit which is useful in removing DC error offset in a signal. Finally, we have a high pass filter (cut-off frequency 194Hz, depending upon the input signal) to get rid of any DC offset and low frequency noise.
3. SIGNAL CONDITIONING – Rectification: This phase, as the name suggests, has a full wave rectifier circuit. This is because our input signal (EMG) has both positive and negative values (as EMG signals are difference of potential). Hence, to attain all values of the input signal we need to completely rectify it.
4.  SIGNAL CONDITIONING - Smoothing + Amplification: The final stage dwell with smoothing the signal and amplifying the final output. This circuit consists of an amplifier coupled with a low pass filter (cut-off frequency 10Hz) to turn our AC signal into a DC voltage. Finally, the amplifier is attached to a trimmer configured as a variable resistor in order to change the overall gain with respect to the strength of the input signal.

Final Deliverable of the Project

Hardware System

Core Industry

Medical

Other Industries

Health

Core Technology

Wearables and Implantables

Other Technologies

Others

Sustainable Development Goals

Good Health and Well-Being for People

Required Resources

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