nivek@scythe.frc.ri.cmu.edu (Kevin Dowling) (09/19/90)
I led electronics design, fabrication and assembly for the Ambler. Ambler, environmental and personnel safety has been paramount since day 1. The Ambler has more than an abort button, it has a piece of hardware called the Safety Circuit which has several hundred inputs and outputs to handle manual and computer control and shutdown. The Safety Circuit is a 3-state FSM implemented in a PAL that transitions between Man/Auto/Kill states based on conditions such as motion limits, amp faults, kill switches, etc etc. I also had a 'heartbeat' be a condition of operation. An I/O line is strobed regularly by the main control processor and if this goes away the machine is shutdown. Shutdown causes all motions to be cancelled, all brakes to be locked and the machine to lock-up. This is the best scenario for this, although it is possible to envision dynamic situations where this might not be best. Lock-up seems to be the best over-all. Manual mode allows an operator to move any link on the machine. Gain adjustment are provided for this. The Safety Circuit is two large circuit boards rack mounted that hold the switches, connectors and relays and the circuitry to support Man/Auto/Kill modes. It is functionally between the controller hardware (VME cage with processors, I/O, motion control etc) and the connections to the machine hardware. Future extensions include a pendant to allow control once all the hardware moves on board the Ambler. As far as safety in operations, any motion of the Ambler is capable of exerting very high forces and we've demoed some crushing capabilities ala David Letterman style to give people some respect for the Ambler motions! A large overhead crane is used as a safety device for early walking motions. We've built a number of large machines (for Three Mile Island, Locomotion Emulator, Navlab) and have pretty good experience running them and the machines needed to build them. nivek Kevin Dowling Robotics Institute Carnegie Mellon University Pittsburgh, PA 15213