Interface Specification
Hardware-based signaling protocols control the transfer of circuit boards between consecutive machines in a surface mount assembly line. System integration relies on smema interlock cables to manage the flow of workpieces and prevent boards from colliding on conveyors. The system uses simple dual-line digital signals to communicate whether an upstream machine has a board ready and whether the downstream machine is busy.
This basic handoff mechanism prevents mechanical damage to the boards and minimizes conveyor jams. The physical connection utilizes a standard four-pin connector and isolated optocouplers to prevent ground loops between different machines.
Signal Progression
The handoff starts when the upstream machine asserts the board available signal, indicating that an assembly is ready to be transferred. Once the downstream machine is idle, it asserts the machine ready signal to initiate the conveyor motors. After the board is successfully transferred, both signals are de-asserted to complete the cycle and prepare for the next workpiece.
Protocol Limit
While highly reliable, this legacy signaling scheme cannot transmit tracking data, serial numbers, or board dimensions. Upgrading to modern standards is necessary when the assembly line requires trace-ability or dynamic conveyor width adjustment. However, the legacy interlocks are still widely used on simple conveyor sections where only basic traffic control is needed.
