Lower Limb Mobility Assistance Using Soft Robotics

People, who suffer from stroke or meet an accident, face a decreased muscle strength which results in reduced mobility. This adversely affects the patient?s daily life activities. Physical therapies can help in improving the lost functions. Traditional rehabilitation therapies for mobility are labor

Project Title

Lower Limb Mobility Assistance Using Soft Robotics

Project Area of Specialization

Robotics

Project Summary

People, who suffer from stroke or meet an accident, face a decreased muscle strength which results in reduced mobility. This adversely affects the patient’s daily life activities. Physical therapies can help in improving the lost functions. Traditional rehabilitation therapies for mobility are labor intensive and usually require assistance of two or more therapists to perform them. In order to control decreased mobility, lower limb hard exoskeletons have been introduced. These suits assist the wearer with mobility by providing external force/ strength to the weak muscles of the lower limbs. Though numerous designs and features have been introduced in the Exosuits, but major drawback is their bulky structure, expensive hardware and difficult user compatibility. A wearable lower limb exosuit based on McKibben pneumatic actuators is presented, designed specifically as a rehabilitation tool for patients with knee injuries and for providing assistance in their daily lower limb motions. The designed system is intended to provide the user with a low cost yet efficient rehabilitation tool, which they can use on their own to carry out the physical therapies associated with the lower limb movement. The key feature of the designed device is its soft actuators that are light-weight and are fixed onto an elastic knee sleeve. Equipped with an Inertial Measurement Unit (IMU), the prototype senses the knee motion and using effective algorithms to control the expansion and contraction of the actuators and assist the wearer with the motion. To evaluate the performance of the device Electromyography (EMG) sensors are placed on the muscles which measure their activity during the knee extension and flexion.

Project Objectives

The objectives of the proposed system can be classified as follows:     

• Design a soft knee exosuit using pneumatic artificial muscles providing mobility assistance.
• The proposed system should be low cost, lightweight, easy to wear and manufacture.
• The system can be used as a rehabilitation tool for people with knee injuries or stroke patients with personalized rehabilitation exercises that can be performed on their own.
• The exosuit consist of McKibben pneumatic artificial muscles they are light weight Can offer high force to weight ratio in comparison to other actuators, similar performance as biological muscles. 

Project Implementation Method

A soft actuator based flexible knee exoskeleton is designed, as a rehabilitation tool for patients with knee injuries.

To design the system following steps are involved: 

• Soft Pneumatic Artificial Muscle Design and Fabrication
• Control Board for the system
• Fabric Knee Sleeve embedded with the complete actuators and control board

Soft Pneumatic Artificial Muscle Design and Fabrication:

The proposed muscles consist of the following parts: 

• Inner elastic tube:? The inner tube expands when air pressure is applied.?
• Braided mesh:? It translates the radial expansion of the inner tube into linear contraction. 
• Connectors:? These? connectors provide? not only help in connecting the actuators with the air supply but also hold together the complete actuator muscle.

The proposed fabrication process of pneumatic artificial muscles is as follows. 

1. Mold designing: 

For inner tubing 3D molds are designed on fusion 360. The molds of the actuator consist of mold body (2 pieces), base stand, cap and placement piece for the top of the rod. Molds are printed using 3D printer

1. Casting:

Once the molds are printed RTV silicon are used to fill the molds for the fabrication of inner tubing. Put the mold for 36 hours at room temperature and then open it. Remove the molded inner tubing and insert into the braided mesh Control Board and Sensors:

The control unit consists of following components. 

• Microcontroller to control various components and to get sensors reading. 
• Air pump to pump the air pressure into the actuator. 
• Motor driver module (L239D) to drive the motor of the pump. 
• Two solenoid valves to control the flow of air pressure into the system. 
• Pressure sensor to measure the inner pressure of the actuator. 
• IMU sensors for reading the movement and orientation of the knee. Based its reading the programmed Microcontroller will send a signal to the board to control the flexion and extension of the actuators. 

Fabric Knee Sleeves:

A fabric knee sleeve is used to place the actuators around knee joints. 

The sleeve is flexible and comforting. it provides maximum body conformity while flexing the knee. 

Benefits of the Project

• The proposed system is designed to be low cost yet effective.
• Physical therapies are time consuming and tiring, patients often discontinue due to this, the proposed system will act as a rehabilitation tool which a patient can use while carrying out his daily choirs and can improve his knee movement on his own without the help of a therapist etc. 
• It is body comforting, ergonomic and easy.
• Current exo suites and robotic systems used for rehabilitations are heavy and bulky. Patients comfort is often sacrificed over the performance of the suits. 
• The system will be open sourced providing all the necessary plans and designs to replicate and improve the system.

Technical Details of Final Deliverable

The proposed prototype is divided into three main parts

• Knee Sleeve embedded with McKibben pneumatic actuators:

The pneumatic actuator is placed on flexible fabric knee sleeve to provide assistance during knee motions.

• Wearable electronic enclosure to control and provide power to the actuators:

The control system will generate a control signal for designed device to control the contraction and expansion of the actuators during expansion and flexion of knee. The board can be controlled using an open source microcontroller device (e.g. Arduino), pressure sensor and IMU.

• Software’s used to interface the electronic board and soft actuators:

LabVIEW based interface of the actuators with designed control system. On the basis of the motion analysis from IMU, the developed device will assist the users in their knee motions. 

Final Deliverable of the Project

HW/SW integrated system

Type of Industry

Medical , Manufacturing

Technologies

3D/4D Printing, Robotics, Wearables and Implantables

Sustainable Development Goals

Good Health and Well-Being for People, Affordable and Clean Energy, Decent Work and Economic Growth, Responsible Consumption and Production

Required Resources