“If no one answers your call…..Then walk alone…(be not afraid) walk alone my friend…!”

                                                                                                                                     – Tagore

Yes my friend you can walk alone even if you’ve difficulties in lower extremity without leaning on someone. Evolution in technologies making our lives more robotic everyday.Depending upon a machine or a robot is rather acceptable than a human nowadays because of our “Fast and Furious” lifestyle.

So here comes the importance of assisting device in mobility for specially patients with disabilities in Sit to Stand motion,Ball and socket joint motion and linearly walking motion.

Before designing a machine or assistive device for a patients we need to know what kind of joints we have in our human bodies and which joint allows us what type of  movements.So different types of movement between different joints are like  —-

  • Uni-axial joint or pivot joint — allows rotational movement
  • Uni-axial joint or hinge joint — allows flexion/extension movements
  • Bi-axial joint or Condyloid  joint — allows flexion/extension, abduction/adduction, and circumduction movements
  • Bi-axial joint or Saddle  joint — allows flexion/extension, abduction/adduction, and circumduction movements
  • Multi-axial joint or Plane joint —  allows inversion and eversion of foot, or flexion, extension, and lateral flexion of the vertebral column
  • Multi-axial joint or Ball-and-socket joint —  allows flexion/extension, abduction/adduction, circumduction, and medial/lateral rotation movements.

Natural motion between these joints and muscles ensure minimum stress in them and stimulates in walking.If the patient can move their leg at minimum level they can undergo physical therapy, gait training , robot aided gait training and body weight supported treadmill walking etc.

To make a device for real world we can go for certain joint movements only because inserting all of the joint movements  in a single device would be less feasible and highly costly,so it might not be able to reach to everyone.

For designing a device for a certain movement or certain motion for human being we can go for different types of mechanisms .

some of them are following :

  • Four-bar mechanism:It is the most fundamental and simplest movable closed chain of the plane kinematic chain.It is a much preferred mechanical device for the mechanism and control of motion due to its simplicity and versatility.It consist of four rigid links called bars connected in the form of a quadrilateral by four pin joints.                                                                                                         According to Grashof’s Law a four-bar mechanism has at least one revolving link if the sum of the lengths of the largest and shortest link is less than the sum of lengths of other two links.

    four bar

    Four-bar Mechanism

    Image source: Google

  • Six-bar mechanism: It is consist of six rigid links and seven joints with one degree of freedom.                 Example – Klann linkage

six bar

Six-bar Mechanism

Image source: Google

  • Eight bar mechanism : It consist of eight rigid links and ten joints with one degree of freedom. It is a rare mechanism as compared to Six-bar and Four-bar mechanism.                                                                                             Examples: Peaucellier–Lipkin linkage and Jansen’s linkage

                                                8 bar

                                                            Eight-bar Mechanism

                          Image source: Google

  Some other mechanisms can be invented for a special kind of assistive device.

Purpose of Designing a assistive device for a patient with disability in lower extremities is to give them assistance in balance and stabilize motion during walking.