Brushless Slip Ring for High Power Transmission

Abstract

Honeybee Robotics Spacecraft Mechanisms Corporation (Honeybee) has developed a brushless slipring (the Rolling Contact Connector, or RCC), which has demonstrated the ability to outperform traditional rotary signal transfer solutions in power density and operational life. Efficient, reliable, high-quality transfer of electrical power has been a goal in the design of spacecraft mechanisms since the inception of the first artificial satellites. Slip rings, and to a lesser extent twist capsules, have served this purpose for decades, however, little has been done to advance the technology in radical, fieldable ways. The intrinsic sliding friction of the slip ring contact interface, increases parasitic torque and inevitably leads to performance degradation and shortened operational life. These issues are magnified in high power slip ring designs, which utilize additional brushes and increased inter-contact preloads. RCC technology is robust, enabling high power and sensitive data signal transfer; and flexible, possessing the ability to merge with existing slip ring technology to form hybridized rotary signal transfer solutions. In this paper, we present an overview of the RCC technology, developed and patented by Honeybee, and present electrical and mechanical figures of merit obtained through research and experimentation. 1. BACKGROUND It is common for robotic or mechanical systems to incorporate some sort of rotating interface; and more often than not, electrical power and/or data are required to pass across that interface. Currently available electrical transfer technology includes: slip rings, twist capsules, and flexible service loops; each of which has its benefits and down-falls. Twist capsules and service loops are limited in rotation and cannot support continuous 360° movement. They also have a relatively large parasitic torque associated with their operation. Slip ring technology is limited to the mechanism by which it works. It relies on some combination of stationary brushes and a rotating shaft. The brushes contact the shaft on conductive rings separated by a dielectric. The downfall of a slip ring lies in the sliding contact between the brushes and the rotor. Sliding friction requires some form of lubrication and causes component wear and debris generation (1). Sliding contacts also suffer from a stick-slip motion profile, particularly at low speed operation. The stick-slip behaviour results in inconsistent parasitic torque and inter-contact conductivity. These sliding contact induced effects reduce the operational lifetime of a slip ring, as well as increase the noise present on data channels. In addition, slipring performance can be degraded due to excessive vibration. Honeybee's Rolling Contact Connector (RCC) technology eliminates each of these limitations. RCC technology is centered on the concept of using a rolling contact interface to transmit electrical signals. A typical RCC signal path is configured similarly to a planetary gearhead and contains three major components; the inner ring, flexible planets, and the outer ring (Fig. 1).