New Three-Degree-of-Freedom Quad-Actuator Payload-Pointing Platform with Fault-Tolerant Reconfiguration Capability

A payload-pointing parallel platform installed on a satellite is an orientation-tracking manipulator for maneuverable payloads. For space applications, the demand for lightweight and high reliability with fault tolerance brings challenges to the design of payload-pointing platforms. In this research, we propose a novel quad-actuator pointing platform with fault-tolerant reconfiguration capability. The proposed quad-actuator platform (QAP) is a special parallel mechanism with four limbs with three independent rotational degrees of freedom. First, a detailed fault-tolerant reconfiguration strategy is presented regarding two major malfunction modes of the voice coil motor in each limb. The two malfunction modes are open-circuit faults and short-circuit faults. Next, the closed-form kinematic model of QAP is derived concerning each fault-tolerant reconfiguration mode. We show that QAP possesses at least two independent rotational degrees of freedom, which is sufficient for orienting axisymmetric payload. Last, maneuvering performances, including workspace, singularity, and fault-tolerant operability, verify the orientation tracking capability of QAP. In summary, due to its lightweight, reliability, and mobility, QAP is a good candidate for the payload-pointing platform of agile and high-precision satellites.