The underlying architecture is 3-RRS mechanism. It is a modification of a 3-RRS spherical mechanism, where all revolute axes intersect at a point, with the end-effector performing a spherical motion. Human head has six degrees-of-freedom, predominantly rotation with a small translation. Our design uses a 3-DOF mechanism to best fit the 6 DOF motion by optimizing the design parameters.
We start by characterizing the head motion of a human subject. We place infrared markers on the head and shoulders of subjects and used motion capture system to record the head kinematics during movements.These data, along with the underlying structure, was used to optimize the design parameters of the mechanism. This was later turned into a prototype.
With the wearable brace, it becomes possible to use it as a measurement tool for head/neck movement. We added potentiometers on the proximal revolute joint in each chain to measure the joint angles. The orientation/position of the head can be, therefore, computed using the forward kinematics. We validated the accuracy against VICON motion capture system.
The brace can deliver desired motion/support to the head with motors. We used a joystick as an input device. The system has two operation modes: (1) axis mode in which a user can rotate the axes of the joystick to move the head; and (2) button mode in which a user can click on buttons to incrementally move the head and provide steady support at different configurations.