Articulating Boom Lift

Overview

An articulating boom lift, often called a knuckle boom, is a self-propelled aerial work platform that carries one or two workers up to a working height of 16-26 m. What sets it apart from a straight telescopic boom lift is the jointed Articulating Knuckle Joint in the middle of the boom. That joint folds and unfolds, so the platform can travel up and then back over an obstacle rather than only straight out. A worker can be lifted past a parapet, over a row of pipework, or in through a gap in a structure and still reach a point set back from the machine. The machine drives itself around a site on its own Drive Chassis and positions the boom over a full circle on the Turntable & Slew, so it works close in around buildings, plant, and steelwork where a scissor lift or a straight boom cannot reach.

The reach geometry is the product of three boom motions working together. The Lower Boom & Riser lifts the knuckle off the turntable, the knuckle folds the upper boom up and over, and the Upper Boom & Jib telescopes out to set the final horizontal distance. Throughout all of this the basket is held level, so the occupants stay upright no matter how the boom is folded.

Chassis and Stability

The Chassis Frame is a welded high-tensile steel box-section structure carrying the axles, the Cast Counterweight, and the slew ring. All four wheels drive and steer: each carries an Wheel Drive Motor with an integral Planetary Wheel Hub planetary reduction, and each wheel end is turned by an Steering Cylinder for two-wheel, four-wheel, and crab steering modes. The wheels are Foam-Filled Wheel foam-filled non-marking tyres that cannot puncture on site debris, and a Wheel Parking Brake on each holds the machine on grade when hydraulic pressure drops to zero.

A machine that lifts a person 25 m into the air has to stay upright. An Oscillating Axle keeps all four tyres loaded on rough ground while travelling, then locks out hydraulically once the boom is raised so the wheelbase becomes rigid. A Chassis Tilt Sensor reads chassis slope on two axes and inhibits boom functions if the machine is parked on more than about 3-5 degrees. The cast Cast Counterweight of 1.5-3 t keeps the combined centre of gravity inside the wheelbase at full outreach.

Turntable and Slew

The whole upper structure sits on the Slew Ring Bearing, a four-point-contact ball slewing bearing about 1 m across with internal gear teeth. The Slew Drive Gearbox is a self-locking worm-gear gearbox built around a Helical Gear Pair and Gearbox Housing, turned by a Slew Hydraulic Motor. Worm gearing is chosen because it holds position under load without a separate brake and gives the slow, controlled 360 degree rotation needed for fine positioning. Because the turntable rotates continuously, oil and signals cross the joint through a Rotary Manifold rather than through hoses that would wind up.

The Boom Linkage

The Lower Boom Section is pinned to the Turntable Weldment and raised by the Lower Lift Cylinder. Alongside it runs the Riser Parallel Linkage, a parallelogram that keeps the upper structure level as the lower boom rises. The Knuckle Weldment joins the lower boom to the upper boom, and the Knuckle Cylinder acting through a Knuckle Bell Crank bell crank folds the upper boom through about 135 degrees. That fold is what delivers the up-and-over clearance.

The Upper Boom Base Section carries the telescoping Upper Boom Fly Section, driven by the Telescope Cylinder and sliding on Boom Wear Pad pads. At the tip, an Articulating Jib swung by a Jib Cylinder gives a final 1.5 m of articulated reach for placing the basket precisely against a structure. A Cable & Hose Carrier energy chain carries hoses and wiring along the telescoping section without snagging. Every pin joint runs on a Boom Pivot Bushing to cut wear and grease intervals.

Platform and Leveling

The Platform Basket is a steel or aluminium cage with a 1.1 m guardrail, toeboards, and a self-closing gate, rated for 230-300 kg. It hangs from a Platform Rotator that swings it about plus or minus 80 degrees so the occupants can square up to the work. Leveling is automatic: a master cylinder at the boom heel is hydraulically linked to a slave Platform Level Cylinder at the platform, so as boom angles change the basket stays horizontal. The Platform Control Box box holds proportional joysticks, and a Foot Enable Switch must be held before any function responds. A Platform Load Cell disables motion if the basket is overloaded, and Lanyard Anchor points take the occupants fall-arrest lanyards.

Hydraulics and Power

The Main Hydraulic Pump is a variable-displacement piston pump delivering about 60 L/min at up to 240 bar, feeding the Proportional Valve Block proportional spools. A Counterbalance Valve on each boom cylinder holds the load and prevents runaway descent if a hose bursts. The Hydraulic Reservoir, Hydraulic Oil Cooler, and Hydraulic Hose Set complete the circuit, with Pressure Sensor units feeding load data back to the controllers. Power comes from either a Diesel Engine with a Diesel Fuel Tank for outdoor work or a Battery Pack and Electric Drive Motor for emission-free indoor use, cooled by the Engine Radiator on the diesel version, with a Power Supply for the control electronics.

Control and Safety

A Machine Control Unit arbitrates the platform and Ground Control Station inputs over CAN and drives the valves. The Envelope Limiter reads the Boom Angle Sensor and Telescope Length Sensor data along with platform load to keep the basket inside the rated reach envelope, slowing or stopping any motion that would push the machine toward instability. The ground station carries duplicate functions and an emergency-lower valve for rescuing an occupant, a Wire Bundle runs the harness from chassis to platform, and a Alarm & Beacon with motion alarm warns people working below.