If a person's spinal cord is injured between the C5 and C7 vertebrae, it will be nearly impossible to grasp and lift large or heavy objects. Sufferers can usually still bend their wrists upward and move their fingers slightly, but they simply cannot hold objects firmly enough. This is where the dorsal gripper comes in. The device, currently in the prototype stage, was developed by associate professor Hannah Stewart, doctoral student Andrew McPherson and postdoctoral researcher Jungpyo Lee in the UC Berkeley School of Engineering.
The dorsal grasper consists of a commercially available padded wrist rest and a motorized hand mounted on it. The hand in turn consists of two articulated polymer fingers with silicone grip pads on the base, and a rubber "artificial palm" that is Velcro-mounted to the back/top of the wristband.
When the user bends their wrist upward, a bend sensor located within the wristband detects this movement. It responds by activating the hand's electric motors, which straighten the spring-loaded fingers upward via integrated steel wire bars.
Once the user moves their arm to place the target object between the fingers and palm of their hand, they bend their wrist downward again to tuck their fingers toward the object. They can then safely lift and move the target until their wrist is bent again.
The dorsal gripper also has a distance sensor that uses a laser to measure the distance of the hand from the target. The device prevents premature activation of the fingers due to involuntary movements of the wrist, as it will not allow the fingers to close if the target is more than 60 mm (2.4 inches) away.
Importantly, the device not only provides a stronger grip than would otherwise be possible, but also allows users to grab items in different directions. Typically, people with quadriplegia often have to turn sideways to grab the object they want to grab, and may be blocked by obstacles such as table legs.
"What's great about this device is that you can use one hand to grab almost anywhere your arm can reach, which greatly expands your workspace," McPherson said.
A paper on the project was recently published in the journal IEEE Transactions on Neural Systems and Rehabilitation Engineering. You can see DorsalGrasper in action in the video below: