Design of a Wearable Scissored-pair Control Moment Gyroscope (sp-cmg) for Human Balance Assist

Our research examines the feasibility of usign a wearable scissored-pair control moment gyroscope (CMG) for human balance assist. The CMG is a momentum exchange device consisting of a fast spinning flywheel mounted on a gimbal. The gimbal motion changes the direction of the flywheel rotation axis, which generates a reactionless torque. A scissored-pair CMG has the additional advantage of isolating the output torque to a single axis, where off-axis torques are canceled out. A properly designed CMG device worn as a backpack can apply a torque in the sagittal plane of the human trunk. This can help in restoring postural balance and in fall mitigation. This paper describes the complete design process of a scissored-pair CMG device with constraints on size, mass and dynamic properties for human wearability. A prototype of this device is built, utilizing a novel dual-flywheel design; it weighs about 8kg and is able to generate over 20Nm of torque. A custom hardware is built specifically for verifying the torque output of the device. To our knowledge this is the only device that generates the range of reactionless torque given its weight and size. INTRODUCTION Reactionless actuators such as Control Moment Gyroscopes (CMG) and inertia wheels [1] are able to apply actuation torques through the exchange of angular momentum without requiring external forces acting on the body. Such devices have traditionally been employed to control the attitude of satellites, boats and ∗Address all correspondence to this author. submersible vehicles [2, 3]. We envision the use of such devices in applications of balance assist for humans. Figure 1 shows the prototype device that we have designed and built (left), which can be worn as a backpack (right). FIGURE 1. Left: A scissored-pair CMG prototype. Right: The same device worn as a backpack. Most of the existing commercially available products are not fit for human wearability due to their excessive mass or insuffi1 Copyright c © 2014 by ASME cient torque. They are geared towards the control of large satellites with masses of up to 1000kg (e.g. Honeywell M50 [4], Astrium 15-45S [5]) or significantly smaller cubesats with sub 10-kg masses (Honeybee TORC [6]). However, these applications have unique requirements of being able to withstand the conditions of space, thereby significantly increasing their mass and cost. Even larger CMGs designed for ship stabilization (e.g. Seakeeper M-series [7]) are also commercially available. A schematic overview of some existing CMGs is shown in Figure 2; commercially existing products fall in the ranges applicable for Cubesats/Nanosats, large satellites and ships. However, none of the devices shown in the range applicable for human assist (up to 10kg, 0.5-50Nm) exists commercially, as each of these proposed or actual prototypes are custom designs. Note that some are proposed but not known to have actually been built. Proposed designs by the authors of [8–10] are shown as examples of devices satisfying the applicable range of mass and torque for human assist, along with the prototype design for our SP-CMG outlined in this paper. 0.01 0.1 1 10 10