Rigidly attached face cams 1 and 2 turn about fixed axis B and have profiled grooves a and b. Followers 3 and 4 turn about fixed axis A and carry rollers 5 and 6 which roll and slide along grooves a and b. The cams are turned by flexible link 7 which runs over pulley d, rigidly attached to the cams. When cams 1 and 2 turn, followers (levers) 3 and 4 are turned about axis A and operate the two-arm semaphore.
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