A hybrid and compact spherical mechanism of large workspace and output torque with unlimited torsion for hand-held gimbal

A hand-held gimbal is a portable mechatronics spherical motion device or robot that used to stabilize a phone or a camera for ease of high quality video or picture shooting. And it's designed to be light, compact and of large workspace for portability and general applicability. In the electronic consumer markets, all the hand-held gimbals are realized by assembling a 3DOF serial orthogonal mechanism on the top of a hand-held stick, benefitted from the simplicity and large workspace of this structure. However, carrying this top-heavy structure for long time shooting makes people getting tired. However, this serial top-heavy structure is not portable and compact enough because it makes people getting tire for a long time shooting and because it is inconvenient to be stored due to the open chain structure. On the other hand, there is no hand-held gimbal that is realized by parallel or hybrid structure although the structure can be more compact and portable, which is mostly due to the small workspace and complexity of the structure. And the existing parallel or hybrid structures in the review works are not suitable to realize a tiny and portable hand-held gimbal. Therefore, a hybrid spherical motion mechanism is proposed in this paper. It contains a PRS-PSS-U parallel mechanism with a passive universal joint and a serial flat brushless motor on the top. While the PRS-PSS-U parallel mechanism acts like a universal motion, the flat brushless motor can rotate unlimitedly. A prototype that has a reachable workspace much larger than a cone of 120° with unlimit torsion is proposed, analyzed and optimized. The prototype is of 45mm diameter and of 130mm height and has respectable output torque to stabilize a camera or smart phone. This tiny and compact structure make it more portable than the existing hand-held gimbals. And the center-heavy structure makes it more comfortable for long time shooting.