Mechanical concept & features Frame & Tier Design Four identical rectangular tier frames made from 20×20 mm or 25×25 mm square aluminum tubing (wall thickness 2–3 mm). Each frame has cross members to support a removable tray (mesh tray or solid tray with perforations). Each tier frame has folding legs or telescoping vertical posts such that frames can nest/stack when collapsed. Two vertical guide rails (aluminum tube) on each side act as the mast for raising/lowering. Collapsible / Nesting Mechanism Each tier's legs are hinged to fold flat inwards; when folded the four frames stack on top of one another. Use quick-release hinge pins to lock/unlock leg position. Alternative: use sliding/telescoping vertical posts that allow tiers to slide down and nest. Pulley Lowering System Each tier is supported by a lift sling/plate attached to a pair of cables (one cable each side) that run up over top sheaves (pulleys) to a central manual winch or geared hand-crank (or small electric winch). Use counterbalanced pulleys or a worm-gear hand winch (self-locking) to prevent accidental lowering. A simple block-and-tackle with 2:1 or 3:1 mechanical advantage reduces effort. Each tier has its own cable/winch line (so tiers can be lowered independently) or a common winch with selectively engaged locking pins for each tier. Safety Locks / Supports At each working position, provide mechanical locking pins (spring-loaded detents) that engage automatically when tier is raised to its lock position. Limit stops (rubber bumpers) to prevent overtravel. Secondary safety catch (safety clamp) under each tier when lowered for prolonged access. Pulley & Cable Specifications Stainless steel braided cable (1.5–3 mm diameter) with swaged end fittings. Pulleys with ball bearings (nylon sheave or stainless). Sheave diameter ≥ 6× cable diameter to reduce fatigue. Winch capacity selected for worst-case load × safety factor (see load calc). Accessibility Improvements Lowering a tier to ergonomic height (~700–900 mm from floor) for feeding and disinfectant dusting. Provide catch-trays or removable trays that slide out for washing. Markings for tier number and weight limits.