Abstract: A proximity sensor is provided for a machine which has a perimeter guard around the periphery of the frame of the machine. The machine has at least a moving part moved by the drive and with a control circuit to control the drive. The perimeter guard includes a radiation transmitter to project a radiation beam at least part of which extends outside the periphery. The perimeter guard further has movable mirrors and a movable bumper which, when moved, inhibit a radiation receiver from receiving the radiation beam. In this case, an output indication is generated to control the drive and stop the machine part. The foregoing abstract is merely a resume of one general application, is not a complete discussion of all principles of operation or applications, and is not to be construed as a limitation on the scope of the claimed subject matter.