Power supply overlaid communication and common clock delivery for cooperative motion control

The aim of our research is to investigate how a common clock signal and control signals can coexist in a newly developed communication system in which various servo controllers are connected to a controlling master via a power supply line a bus topology. A major problem tackled by this research is how synchronized actions of the servo motors can be achieved. In order to synchronize the actions, the starting time of the actions must be accurately controlled. For this purpose, the transmission of a common clock signal is introduced which uses Direct sequence spread spectrum (SS) modulation in the same frequency band as the control signals. To avoid the interference of the common clock signal to the control signals, an interference cancellation method, in which a regenerated SS signal is subtracted prior to the demodulation of the control signals, is employed. Symbol error rate of the control signal, and probabilities of false alarm and miss detection of the common clock pulses are analyzed. The coexistence of the common clock and control signals is confirmed, under the experimentally obtained channel parameters.