Development of a Parallel Robotic Positioning System With Specific Workspace for Noninvasive Brain Stimulation

Brain stimulation using noninvasive methods has been widely adopted in neuropsychiatric disorder therapies. Clinicians who use the innovative methods situate the stimulator manually in a typical setup. However, this causes practical difficulties in precisely locating the stimulation device at a desired pose. This article proposes a robotic positioning system that can precisely position a brain stimulation device at the desired pose. The design concepts are focused on the development of a system with a workspace specialized in noninvasive brain stimulation. To stimulate the overall area around the upper part of the head, the system is designed to have a specific posture with a six-degrees-of-freedom (6-DOF) movable parallel mechanism and a 1-DOF extra revolute joint. The combined system not only significantly increases the workspace of the system but also increases its physical safety. In the movable parallel mechanism, we realize sufficient mobility for the robotic device using three-<inline-formula><tex-math notation="LaTeX">${\bar{\bf{P}}}$</tex-math></inline-formula> <underline>R</underline>PS chains (<inline-formula><tex-math notation="LaTeX">${\bar{\bf{P}}}$</tex-math></inline-formula>: curved prismatic joint, R: revolute joint, P: prismatic joint, and S: spherical joint). The curved prismatic joint (<inline-formula><tex-math notation="LaTeX">${\bar{\bf{P}}}$</tex-math></inline-formula>) is a revolute joint realized by curved rail and enables efficient movement of the stimulator around the subject's head. Furthermore, the parallel mechanism offers good physical safety and load-carrying capacity. The moving platform, which is close to the head, exhibits low inertia, and there is no rapid change in the acceleration due to the failure of control because the moving platform is moved as a combination of joint movements. The system can accommodate stimulators of varying weights, such as those employing transcranial magnetic stimulation and ultrasound transducers. A prototype of the proposed system was developed using the design specifications, and its performance was verified experimentally.