Abstract: A particle-free dockable interface is disclosed for linking together two spaces each enclosing a clean air environment. The interface is composed of interlocking doors on each space which fit together to trap particles which have accumulated from the dirty ambient environment on the outer surfaces of the doors.

Abstract: A laser transmitter emits a beam which scans about a scanning axis to effect a curtain of light which defines a boundary of a working space. Photosensors mounted on the outboard portion of a crane or other construction equipment generate warning signals to the construction equipment operator and other nearby personnel whenever these photosensors move into the light curtain. Additional curtain sensing equipment positioned to intercept the rotating laser beam with each cycle of rotation develops an alarm signal which activates an alarm horn and/or alarm light whenever the laser transmitter fails to provide the light curtain.

Abstract: Apparatus for selectively discharging load carriers at a predetermined one of discharge stations. The carriers are connected to an endless chain. The chain is made of links of approximate equal length, which are divided into segments of an equal number of links. The position of each carrier is determined by a control system that measures the actual length of segments of the chain and keeps a record of the lengths of the segments which extend between a reference point and the position of the each carrier. When the length of the chain between the reference point and the carrier equal the known distance along the chain path between the reference point and the preselected discharge station a mechanism is actuated to remove the load from the carrier.

Abstract: A method for measuring the length of segments of moving chain includes the steps of measuring the velocity of the chain by timing the interval a point on the chain moves a known distance and timing the interval between the sensing of one end of the segment at one point and the sensing of the opposite end of the segment at another point a known distance from said one point. A method is disclosed to track each carrier in a conveyor system by continuously measuring segments of the chain and maintaining a running total of the chain length between each carrier and a reference point. Apparatus in the conveyor system, including a chain length measuring station, is disclosed.