Switching device for detecting interruptions in transmission lines

In an industrial robot having a teaching and operating board for teaching robot operation, a robot control apparatus for controlling a robot, and a plurality of transmission lines for connecting input signals from said teaching and operating board to said robot control apparatus, a device for detecting interruptions in said transmission lines and for switching said transmission lines comprising:

• a plurality of driver means connected to said teaching and operating board for receiving robot control input signals therefrom, each of said driver means providing a first digital output signal corresponding to said robot control signal and a second digital output signal of polarity opposite to that of said first digital output signal;
• a first transmission line connected to each of said driver means for carrying said first digital output signal and a second transmission line connected to each of said driver means for carrying said second digital output signal;
• a receiver means connected to said first and second transmission lines from each of said driver means for reconverting said first and second digital output signals to a robot control output signal corresponding to said robot control input signal;
• an interruption detecting circuit means comprising an exclusive OR gate and a transient filter connected to said first and second transmission lines from each of said driver means and operable to produce an output signal only when said first and second digital output signals received on said transmission lines are normal;
• a switching circuit means comprising an AND gate having inputs connected respectively to the outputs of the receiver means and the interruption detecting circuit means of each of said driver means and providing an output only when signals are present at both inputs, whereby the receiver means output is disconnected if no interruption detecting circuit means output signal is present;
• and
• an OR gate having inputs connected to the outputs of each of said AND gates and an output connected to said robot control apparatus, whereby only robot control output signals from uninterrupted transmission lines are connected to said robot control apparatus.