One-wire smart motors communicating over the DC power bus-line with application to endless rotary joints

A system of multi-axis networked smart motors is developed to reduce complex cable harnesses. Motor control signals are sent over the DC power bus line and received by motors with integrated power amplifiers and controllers. The noise level and signal attenuation are low, allowing for high fidelity, broadband communication among many smart motors without bulky, costly cables. A modem is designed to exploit the features of the DC power bus communication. A power-signal coupling circuit with an impedance trap filter is designed for superimposing control signals over the DC power bus line with a maximum of signal transmissibility and reduced line noise. An experimental setup was developed to identify the noise spectrum and signal transmissibility of the consolidated power-signal line. Optimal carrier frequency and filter parameters are then obtained based on the experiments. A simple protocol for bi-directional communication between the motors and the central controller is designed and tested. Finally, the design of a joint undergoing continuous rotation is proposed utilizing the consolidated power-signal cable connected to endlessly spinning smart motors.

1. Introduction

Complex cabling places a limitation on servo system design. The precision actuators in servo systems have multiple connections with other motors, a centralized controller, a power source, etc. For servo systems, housing and guidance become problems during, the design phase. It is important that the cabling not restrict the bending and twisting connections. Thus, the cable guidance can become so complicated that automated’ installation is not possible. Such complex designs become problematic when maintenance is required as it may be inconvenient to repair cables without taking the entire machine off-line. Cabling contributes to higher material, manufacturing, and maintenance costs as well-as increased weight and bulk. The number of problems associated with cabling varies directly with the increasing number of axes in an apparatus.