Abstract: A bell crank and a mechanical link are included in an aerial lift system to mechanically constrain motion of a two-boom aerial lift mechanism to prevent the aerial lift system from accessing unstable positions. Typically an aerial lift is coupled to a vehicle via a turntable. The turntable includes a counterweight on a rearward side of the turntable to balance the booms and associated hardware as they are extended in a forward direction. If the booms are in certain rearward, or even vertical positions, the counterweight can cause the vehicle to tip and such unstable positions are to be avoided. By providing the bell crank proximate the pivot joint between upper and lower booms, with the bell crank coupling at pivot joints with: the lower boom, the mechanical link, and an upper hydraulic cylinder, the booms of the aerial lift system are mechanically constrained to avoid vehicle tipping.

Abstract: Apparatuses and methods for controlling the stability of elevating systems, such as personnel lifts. In one embodiment, a stability control apparatus includes an angle detector and a signal processor. The angle detector is mounted to a boom of a personnel lift and configured to detect an angle of inclination of the boom relative to an independent reference frame independent of the personnel lift. The signal processor is operatively connected to the angle detector and is configured to receive a first signal initiated by the angle detector when the angle of inclination reaches a predetermined angle. The signal processor is further configured to output a second signal in response to receiving the first signal causing a boom control system to limit movement of the boom relative to the independent reference frame when the angle of inclination reaches the predetermined angle.