[Design View / Design Solution]
Design Robust, Fault-Tolerant Motion-Control Feedback Systems
Successful designers will understand the key role played by receiver ICs, encoder signal cabling, terminations, and pc-board layout.
Successful designers will understand the key role played by receiver ICs, encoder signal cabling, terminations, and pc-board layout. Today's demanding industrial applications require rugged, reliable robots and automated machines that operate under harsh conditions and run 24 hours a day, seven days a week.
Fortunately, modern high-speed servo systems can be designed for a robust and fault-tolerant motion-control feedback system. Receiver circuits for the motion controller must respond predictably to potential faults, and proper pc layout for the receiver circuit prevents noise problems in the encoder data. A designer should also consider the quadrature encoder's signal cabling, including terminations at the receiver circuit. These precautions will produce a motion-control system that's stable and predictable during fault conditions.
Much of the improved performance seen today results from newer technologies and microelectronics. Those innovations provide more robust automated systems by eliminating robot collisions in shared workspaces, improving task assignments, and honing servo accuracies. The key to robust system operation comes down to how it handles mechanical and electrical faults. To that end, this article discusses the design of a robust and fault-tolerant motion-control system whose feedback paths incorporate quadrature encoders.
HIGHLIGHTS
Servo Systems Automated systems typically include feedback elements to ensure accurate and stable control over speed and position.
Controller Receiver Circuits The controller's receiver converts the quadrature encoder's signals to logic levels for processing. The receiver provides fault detection and ESD protection.
Receiver Circuit Layout Pay attention to board layout to minimize signal imbalance, crosstalk, common-mode noise, and noise coupling.
Encoder Sigal Cable Shielded twisted-pair cable should be used for best performance. The cable should carry only the encoder's signals.
Sidebar: Encoder Types A look at some of the types of components that supply feedback in servo systems.
Sidebar: Fault Types A discussion of the most common faults in control systems and what problems could cause them.
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