The rope gripping device was born out of a very unique problem statement: To enable a C7 Quadriplegic para-athlete to effectively manage a solo sailboat by providing an optimal method of gripping sailing ropes. Our team has been in touch with an inspirational 'customer' for this concept, who will eventually use this device to improve his sailing.
Quadriplegia (tetraplegia) is caused by damage to the cervical spinal cord segments at levels C1-C8. Damage to the spinal cord is usually secondary to an injury to the spinal vertebrae in the cervical section of the spinal column. The name arises out of the fact that all four limbs of the person are affected. The legs are completely paralyzed and the arms are partially affected depending on which segment of the neck received the injury as seen in the list below
C3,4 and 5 Supply the diaphragm (mostly C4) (the large muscle between the chest and the belly that we use to breath). |
| C5 also supplies the shoulder muscles (deltoid) and the muscle that we use to bend our elbow (biceps). |
| C6 Bends the wrist back (extension), and externally rotates the arm (supinates). |
| C7 Straightens the elbow and wrist (triceps and wrist flexors) straightens fingers, pronates wrist. |
| C8 Bends the fingers (flexion). |
| Injury below the cervical spinal segments will result in paraplegia, since the arms would be fully functional, but the legs completely paralyzed. |
| Source for Quadriplegia information: http://www.apparelyzed.com/quadriplegia-quadriplegic.html |
So in the case of a C7, all the functions of C1-6 are normal, the functions of C7 are impaired to varying degrees and those of C8 and below are usually completely impaired. To say that more simply, the movements of the arm are normal, and so is the ability to extend fingers as well as move the wrist; but the flexing (or gripping movement) is almost absent. The only limited control here is a weak gripping movement of the thumb.
This means that a C7 who is a sailing enthusiast or para-athlete would be strong enough to handle the ropes and maneuver a sailboat if only he were given an effective method of gripping ropes. In the specific case of our customer, the arms have enough strength to lift 70 pounds of weight if transmitted to the wrist, but the fingers would barely support a single pound. So given these factors, we started with the following design goals.
Problem Statement
To design a rope gripping device that can be mounted on the hand of a C7 Quadriplegic athlete with the following requirements.
- Capable of gripping sailing lines of varying sizes from 3/8in to 1/2in with a pulling force of 50 pounds
- Pulling force of the rope is to be transmitted to the wrist and not the fingers
- The signal input can come from small movements of the thumb.
- Compact and lightweight device that is easy to remove and put on even during sailing without assistance.
- Durable and water resistant- to be used in a wet and salty environment
- Ability to be continuously used for a minimum of 4 hours of sailing, preferably for a full day without recharging.
- Ability to grab the rope fairly quickly. And to release it instantly if needed.
- Have as few hooks or sharp edges that would accidentally snag a sailing line.