Motion control for AGVs, AMRs and intralogistics

In short:Mobile robots run everything from a 24 V or 48 V battery, so pick low-voltage servo wheel drives sized for the worst combination of payload, acceleration and floor gradient, then check traction, brake holding and run time. The safety case sits under ISO 3691-4, so feedback and drives must support the speed and stop functions it asks for.

Typical requirements

What intralogistics asks of motion components

Automated guided vehicles (AGVs), autonomous mobile robots (AMRs), shuttles and the conveyors and sorters around them have one thing in common: they run for long shifts, start and stop constantly, and work near people. For mobile machines add a second constraint. Every watt comes out of a battery, usually at 24 V or 48 V, so efficiency is run time and current is cable size.

A published example gives the scale. The MiR600 carries up to 600 kg at up to 2.0 m/s on a 47.7 V, 1.63 kWh Li-ion pack, for about 8 h 20 min at maximum payload. It rolls on 200 mm drive wheels, is rated IP52, and lists ISO 3691-4 with 13 safety functions to ISO 13849-1.

Low-voltage servo wheel drives

Most AMRs and many AGVs use differential drive: two driven wheels, each with its own servo motor, reducer, brake and encoder, plus castors. There are three ways to build it.

Integrated units. The Kinco iWMC combines servo motor, drive, 9:1 or 11:1 reducer, brake and polyurethane tyre on 24–60 V DC with CANopen. Its three sizes (150, 165, 180 mm wheels) give 3.6–40 Nm rated and up to 99 Nm peak at the wheel, for robots carrying up to 1 tonne, at 1.9–3.9 m/s.

Separate components. Low-voltage brushless servo motors such as the Kinco SMC low-voltage range (50 W–3 kW, 24–48 V DC, IP65) or the Leadshine ELVM (33 W–2 kW, up to 300% overload) pair with compact drives like the Kinco FD1 or Leadshine ELD2 (24–70 V DC, up to 60 A continuous and 180 A peak, STO SIL3 on the larger models). A low-backlash planetary such as the Apex AB/ABR or a right-angle unit makes up the reduction. See servo and stepper motors, servo drives and gearboxes.

Low-voltage drives carry high currents. A 1 kW axis on 48 V draws over 20 A, and peaks can be several times that. Check the drive’s peak current duration, the contactor and fuse ratings, and the regenerative energy when the robot brakes downhill; batteries accept charge but a full one may not, and many drives need an external brake resistor.

How to size an AGV drive wheel: a worked example

Vehicle 800 kg loaded, two driven 180 mm wheels, top speed 1.5 m/s, acceleration 0.5 m/s², worst ramp 2%. Assume a rolling resistance coefficient of 0.015 for illustration; ask your wheel supplier for the real value on your floor.

1. Rolling resistance: 0.015 × 800 × 9.81 = 118 N.
2. Acceleration: 800 × 0.5 = 400 N (as a rule of thumb, add 5–10% for rotating wheels, rotors and gears).
3. Gradient: 0.02 × 800 × 9.81 = 157 N.
4. Peak force (accelerating up the ramp): 675 N, so 338 N per wheel. At 0.09 m radius that is about 30 Nm per wheel.
5. Continuous on the ramp at speed: (118 + 157) / 2 × 0.09 = about 12 Nm per wheel.
6. Wheel speed: 1.5 / (π × 0.18) × 60 = 159 rpm. With 11:1 reduction the motor turns about 1,750 rpm.
7. Power: about 1 kW total at the end of acceleration, around 21 A from a 48 V pack before losses.
8. Traction: if half the vehicle weight sits on the drive wheels, the wheels need a friction coefficient of at least 675 / 3,924 = 0.17. Wet or dusty floors can cut this sharply, which is why drive wheels are often sprung to keep load on them.

Those figures sit inside the published range of integrated wheel units. Next, build a duty cycle (moves per hour, dwell, charging) to get RMS torque and battery energy per shift. Caster Concepts also notes that polyurethane wheel load ratings fall with speed because the tread heats as it deforms, so check the tyre rating at your speed and duty, not just static load.

Lift, tow and top-module actuators

Mobile robots often carry a lift top, a tugger hitch, a roller conveyor top or a turntable.

• Lift tops use a battery-powered linear actuator, screw jacks driven by one motor, or a scissor mechanism. Heavy-duty 12/24/48 V DC actuators such as the Thomson Electrak HD reach 16 kN with a load-holding ball nut and IP67/IP69K static sealing; the Electrak XD reaches 25 kN at 45% duty. Watch duty cycle: lift tops that cycle every minute can exceed a 25% rating. How to size a linear actuator covers force, speed and duty.
• Synchronised lifts with two or four actuators need position feedback on each and a controller that keeps them level.
• Turntables and rotating tops need a slip ring if they rotate continuously; otherwise a cable loop is simpler.
• Conveyor tops use small 24 V roller drives or an integrated low-voltage servo.

Conveyors, sortation and shuttles

Fixed intralogistics uses the same low-voltage building blocks. Integrated servo motors with the drive on the motor, such as the Kinco MD (200–750 W, 24–70 V DC, 16-bit absolute) built for logistics, or the Leadshine iSV2, remove separate drive cabinets and run on a daisy-chained DC bus and fieldbus. For long-travel stacker cranes and shuttle lifts, cable reels and absolute position feedback on the travel axis are common; a robust linear encoder such as the KappaSense FLEXe tolerates dirt and vibration on axes up to 1.9 m. For multi-axis coordination see motion controllers.

Safety: ISO 3691-4 and what it means for components

ISO 3691-4 covers driverless industrial trucks and their systems. The second edition (2023) replaced the 2020 version and added terms such as “active detection field” and “operational stop”. The standard is applied to the whole vehicle, but its clauses shape what you buy:

• Braking: the stopping function must work when power or control is lost, so spring-applied brakes are standard.
• Speed control and overspeed detection: the safety controller needs trustworthy speed feedback, often a second encoder or a safety-rated one.
• Detection of people in the path: scanner fields switch with speed, so the drive and safety controller must know actual speed reliably.
• Safety-related control parts: these are assessed against ISO 13849-1, so ask drive suppliers for STO and other safe functions to IEC 61800-5-2 with stated PL or SIL.
• Stability: load on lift tops and braking forces affect tipping; actuator speed and acceleration are part of that check.

In North America, ANSI/A3 R15.08 covers industrial mobile robots. Battery truck electrical requirements are in EN 1175.

Typical pitfalls

1. Sizing on flat floors only and finding the robot stalls on a dock ramp or expansion joint.
2. Ignoring traction on wet or dusty floors, so torque is there but the wheel spins.
3. Underrating the brake for a loaded vehicle parked on a slope.
4. Forgetting regeneration when a heavy vehicle brakes or descends.
5. Choosing a lift actuator on force and overrunning its duty cycle.
6. Leaving safety feedback until late, then needing a second encoder that will not fit the wheel hub.

Send us your vehicle mass, wheel layout, speeds, gradients and duty, and our specialist engineering and supply partners can propose wheel drives, lift actuators and controls to match.

Standards to have in view

• ISO 3691-4:2023 (industrial trucks: driverless industrial trucks and their systems)
• ANSI/A3 R15.08-1 and -2 (industrial mobile robots, US)
• EN 1175 (industrial trucks: electrical and electronic requirements)
• ISO 13849-1 (safety-related parts of control systems)
• IEC 61800-5-2 (adjustable speed drives: functional safety, e.g. STO)
• IEC 60529 (IP codes)

Which standards apply depends on the end product and its market. Your engineer will confirm what the component itself needs to meet.