Verifying machine capabilities and making sure it works the way it is supposed to work.
A machine consist of several sensors, actuators and process equipment such as welding, handling, engraving, labeling etc. Programming a machine requires greater amount of time and thinking. There will be poka-yoke checks to make sure the products does not have any missing sub-assemblies or sub-parts from previous stations or steps.
“There is a sensor that detects the presence of a nut welded to the stamping in the previous station. How do you know it actually detects the nut, not the stamping?”
Let us take an example of a spot welding cell. Most machines runs three shifts a day and produce hundreds or parts. The sensor could be in a strong magnetic field during welding and it is repeated over and over again. Most of the sensors has adequate shielding against magnetic fields. But, what if one fails? The machine could produce a bad part and nobody knows about the problem. This is the reason for a special program that check all critical sensors and poka-yoke mechanisms, usually in the beginning of each shift or whenever manually triggered.
A "Red" Rabbit in a group of "White" Rabbits, rabbits being the parts produced, Red means bad and white means good parts. In short the special program is to detect the bad part in a group of good parts. The machine is designed to do this but it is tested using the Red-Rabbit program.
In the beginning of each shift, a part with obvious defect (The Red-Rabbit Part) is introduced to the machine. The machine will be in the special Red-Rabbit program. The machine will be checking for specific sensors. In the example discussed before, the red-rabbit part will be missing a nut and the sensor that is supposed to detect the nut should not turn-on. If the sensor is ON with the red-rabbit part, that is a failed test and indicates a faulty sensor.
The Red-Rabbit program is done in the PLC. This program blocks the normal operation of the cell. Some Red-Rabbit programs involves robots as well. Different companies use different names such as "Boundary Program" or "Poka-Yoke Program" for Red-Rabbit program . Some companies use a bypass option with supervisor or team-lead authorization as well.
The Red-Rabbit program is inevitable in a welding cell to make sure produced parts are good and all rejected or bad parts does not end up in the finished parts bin.
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