Four Problems With AGVs in a Cold Store
A cold store AGV fails for reasons an ambient truck never meets. This article covers the four that cause the most downtime — fogged optics, cold-rated parts, wheel slip, and battery endurance — and what to specify instead.
1. Temperature swings fog the optics
An AGV crossing the freezer doorway fogs up fast. The lens and sensor windows leave a −25 °C room and hit warm, humid air in the anteroom. Condensation forms on the glass within a few seconds.
That matters because navigation and obstacle avoidance both look through that glass. A fogged lidar returns a scattered scan. A fogged camera sees grey. The truck keeps driving on dead reckoning until it drifts off the path or stops against a pallet it never registered.
Three ways to deal with it:
- Anti-fog coating on the optics. Cheapest option, but it wears and needs reapplication at service intervals.
- Heated optics and windows. A heater ring or film keeps the surface above dew point. It costs power, so add the draw to your energy budget.
- One temperature zone per AGV. Keep the truck inside the freezer or outside it, and let a transfer conveyor or a second fleet handle the doorway. This removes the problem instead of managing it.
If you must cross the threshold, give the truck a buffer zone to sit in and clear. A doorway air curtain helps, but it does not replace heated optics on a humid day.
2. Cold-rated components and chassis stability
Ordinary industrial electronics are rated for roughly 0 °C to 40 °C. At −25 °C they behave differently: display refresh slows, capacitors lose capacity, and some controllers refuse to start until they warm up.
The parts that need a low-temperature rating:
| Component | Ambient rating | Cold store requirement | Why it matters |
|---|---|---|---|
| Battery pack | 0 °C to 45 °C | −25 °C rated cells, heated bay | Capacity and charge acceptance |
| Controller | 0 °C to 40 °C | −30 °C rated board | Start-up and current control |
| Lidar / camera | 0 °C to 50 °C | −25 °C, heated housing | Fogging and scan stability |
| Hydraulic oil | Standard ISO grade | Low-pour, low-viscosity grade | Slow lift at cold start |
| Chassis steel | Standard structural grade | Low-temperature toughness grade | Brittle fracture risk |
Chassis materials are the part buyers miss. Carbon steel that flexes normally at 20 °C becomes brittle in a freezer, and a mast or frame that takes a shock load can crack instead of bending. Structural parts for a freezer unit should be specified with low-temperature impact toughness, and welds inspected for the same reason.
Cable insulation is the second one. Standard PVC gets stiff at −25 °C and cracks at the bend radius of a moving mast. Look for a cold-flexible jacket on any cable that travels.
3. Floor moisture, slip, and positioning accuracy
Freezer floors carry a thin film of ice or meltwater, often both. A wheel that slips loses traction and the drive encoder counts revolutions that never reached the floor.
That error accumulates. Odometry alone can drift 200 mm to 500 mm over a 30 m run on a wet surface — enough to miss a pallet pocket or clip a rack leg. It gets worse on ramps and at the doorway where meltwater pools.
Countermeasures:
- Higher-accuracy positioning. Laser navigation with reflectors, or a hybrid laser plus QR/slot-marker setup, corrects drift instead of trusting it.
- Floor reference features. Extra reflectors, floor markers, or magnetic tape at the pick and drop stations. Cheap, and they pin the stop position where accuracy actually matters.
- Traction-aware tuning. Reduce acceleration and braking rates so the drive does not break traction during a start. Slower ramps, fewer slips.
- Floor drainage and squeegee mats at the threshold, to cut the water the truck drives through.
Stopping accuracy at the rack face is the number to hold. Ask for a repeatability figure measured on a wet floor, not on a dry test pad.
4. Charging, discharge, and energy consumption
Cold cuts usable battery capacity. A lead-acid or lithium pack that gives 8 hours at 20 °C delivers noticeably less at −25 °C — often 30% to 50% less depending on chemistry and how the pack is housed. Charge acceptance drops too, so a pack that charged in 2 hours takes longer, and fast charging may be blocked until the cells warm.
Practical responses:
- Recalculate the shift on real cold endurance. Do not carry over the ambient runtime figure. Ask for a discharge curve at −25 °C, or run a trial over a full shift in the actual room.
- Opportunity charging. Charge during natural idle windows — operator breaks, shift change, waiting at a conveyor — instead of one long charge.
- Spare packs and a warm charge bay. Swap the pack at shift change and charge it outside the freezer where the cells recover capacity.
One more consideration: heating the battery bay costs energy that no longer moves pallets. Heated optics, heated lidar housings, and pack heaters together can add 300 W to 800 W of continuous draw. That figure belongs in the sizing calculation, not discovered later.
5. How to choose
- Confirm the temperature band. Ask for the rating at your lowest operating temperature, not an average. A truck rated to −10 °C is not a −25 °C truck.
- Check the optics rating and heating. Heated lidar housing and anti-fog window treatment, or a design that keeps the truck in one zone.
- Ask for a cold discharge curve. At −25 °C, look for a stated working time, not a nominal amp-hour figure.
- Match load and lift to the job. AGV pallet truck CBD20J01 carries 2500–5000 kg with a 200 mm lift, which suits floor-level pallet moves between freezer and dock.
- Size the aisle before the truck. Reach AGV units lift 1500–12000 mm, so confirm your narrowest aisle and rack beam height first.
- Verify stopping accuracy on a wet floor. Ask for repeatability in millimetres, measured in the freezer, not on a dry pad.
- Plan charging around the shift. Opportunity charging plus one spare pack per truck is the usual starting point for a two-shift freezer operation.
6. FAQ
Can a standard AGV be used in a freezer?
Usually not without changes. Optics fog at the doorway, standard controllers are rated to about 0 °C, and the battery loses usable capacity. A cold store AGV differs in the rated components, the heating, and the navigation setup.
What temperature can a cold store AGV work at?
Specify by your actual low point. Most freezer installations run between −18 °C and −25 °C. Ask for the rating at that number and for the components that carry it — battery, controller, sensors, hydraulic oil, and cables.
How do you stop the lidar from fogging?
Three routes: anti-fog coating on the optics, active heating that holds the surface above dew point, or keeping the AGV inside one temperature zone so it never crosses the humid threshold. Heating draws power, so add it to the energy budget.
Does a cold store AGV lose battery capacity?
Yes. Usable capacity falls in the cold, and charge acceptance drops as well. A pack giving 8 hours at 20 °C can give roughly 4 to 6 hours at −25 °C. Size the shift on a cold discharge curve, and use opportunity charging plus spare packs.
Why does an AGV stop inaccurately on a freezer floor?
Wheel slip on ice or meltwater makes the drive encoder count travel that never happened. Odometry error accumulates, so the truck overshoots the stop point. Laser navigation with floor reference features corrects the drift.
What AGV models does WR build for cold stores?
WR builds AGV pallet trucks, AGV stackers, and reach AGVs. The AGV pallet truck CBD20J01 uses laser navigation with a 200 mm lift and 2500–5000 kg capacity; the AGV stacker CDD*J01-16 has a service weight of 820 kg; reach AGV units lift from 1500 mm to 12000 mm.