Motion control for medical devices and lab automation

In short:Medical and lab machines need smooth, quiet, low-cogging motion that the device maker can qualify inside its own safety and quality system. Components are not certified to IEC 60601-1 on their own: the finished device is, so pick parts with the data your risk file needs.

Typical requirements

What makes medical and lab motion different

Medical imaging systems, surgical robots and laboratory automation all move loads that a general machine builder would find small. The difficulty is everything else around the move. The motion has to be smooth at very low speed. It has to be quiet enough for a ward or a lab bench and clean enough for a controlled room. And every part has to be documented well enough to sit inside a device manufacturer’s safety case.

The first point to settle is who owns the compliance. IEC 60601-1 applies to medical electrical (ME) equipment and ME systems: the finished product. A slip ring, motor or encoder is not “60601-certified” on its own. The standard has a dedicated clause on components of ME equipment, and the device maker uses it to show that each part is suitable where it is used. The component supplier provides the evidence:

• Dielectric strength and insulation resistance results, and the insulation class of windings
• Creepage and clearance figures, so the device maker can count means of patient or operator protection (MOPP/MOOP)
• Leakage paths through housings and shafts, which matter for anything near an applied part
• Materials declarations, any component approvals, and EMC behaviour that feeds the IEC 60601-1-2 assessment
• Change notification, so a silent material or process change doesn’t undo your verification

ISO 13485 is the quality management standard for organisations in the device lifecycle. Its scope says suppliers can also use it, but it doesn’t require every supplier to be certified. Your own purchasing controls and risk management to ISO 14971 decide what you need from a motion supplier. Ask your quality team before you shortlist parts, not after.

CT gantries and imaging: large-diameter slip rings

A CT gantry spins the X-ray tube and detector ring around the patient, so the slip ring wraps around the patient aperture. Moog’s published large-diameter range gives a feel for the scale: inside diameters of roughly 32–44 in (about 810–1,125 mm), speeds of 120–300 rpm, power rings at 380–600 V AC carrying 100 A continuous, and an integrated encoder option above 15,000 counts.

Image data comes off the rotor at gigabit rates, too fast for sliding contacts. CT rings therefore split the job. Power stays on brushes. Data crosses a non-contacting link, either RF/capacitive coupling (above 5 Gb/s aggregate on the published range) or a multi-channel optical joint (above 40 Gb/s aggregate). See the medical imaging slip ring page and the large-diameter type for the trade-offs. Series to look at include the Moog CT slip rings and Moog large-diameter assemblies.

What to specify for an imaging ring:

• Bore and envelope, including brush blocks and data-link hardware, which published OD/ID figures often leave out
• Surface speed, not just rpm. At 1 m diameter, 200 rpm means about 10.5 m/s at the track
• Power per ring and in total, with the generator’s voltage and current profile
• Data direction and rate, rotor-to-stator and stator-to-rotor separately, plus the bit error rate your reconstruction tolerates
• Debris and noise limits, because brush dust and audible noise matter in a scanner room
• Service access: brush replacement intervals and whether a field engineer can do it on site

Patient tables, C-arms and radiotherapy couches use the same families at lower speed: heavy-duty linear actuators, gearboxes and absolute feedback so the axis knows where it is at power-up.

Surgical robots: frameless motors, strain-wave gears and dual encoders

Surgical robot joints are packed tightly. Every millimetre of axial length makes the arm wider, which matters when several arms work around one patient. Kollmorgen’s surgical robotics white paper puts it simply: motor stack length drives joint width, and torque rises with the square of rotor diameter. Doubling the diameter gives roughly four times the torque, so the same torque fits in a much shorter stack.

That is why most designs pair a frameless torque motor with a strain-wave gear set. The gear set gives zero backlash, a high ratio in one stage and short axial length. A typical joint also has:

• Two encoders: a high-speed sensor on the motor side for commutation and velocity, plus a high-accuracy absolute encoder on the output to remove gear wind-up and lost motion. Thin hollow-shaft absolute encoders such as the Netzer VLX are built for this. See absolute vs incremental encoders.
• Low cogging: Surgical Robotics Technology notes that cogging is rarely on datasheets, so ask for the absolute value and its frequency. A higher cogging frequency is easier for the control loop to filter.
• Low-voltage drives: the same article recommends keeping the system under 50 V, which suits low-impedance windings. These need drives with a high PWM frequency to keep current ripple down. Compact drives like the Novanta Capitan are aimed at this space.
• A fail-safe brake wherever the arm must hold its pose without power.
• A thermal budget: heat in the joint degrades gear lubricant and can limit the encoder, so you may run the motor below its rated winding temperature. Check torque at that de-rated point.

Gear sets such as the Harmonic Drive CSG are widely used here (Harmonic Drive is a trademark of Harmonic Drive LLC; strain-wave gearing is the generic term). Our frameless motor sizing guide for robot joints and harmonic vs planetary vs cycloidal go into the sizing. The particular standard for these systems is IEC 80601-2-77, which sits on top of IEC 60601-1.

Liquid handling and lab automation: smooth, quiet linear axes

Pipetting heads, plate movers and sample transport run all day in labs where people are working. FAULHABER’s lab automation overview sums up the brief: micrometre-level positioning, quiet cogging-free running, and enough reliability that transport systems can cover many kilometres without wear becoming the limit.

How to choose the axis:

Ironless motors avoid cogging and the magnetic attraction that loads the guides, but PI notes they cost more because they use roughly twice the magnet material. The Akribis AUM is one example aimed at biomedical and inspection stages. Cylindrical voice coils like the Akribis AVM suit short-stroke Z-axes and valve control. For general sizing see how to size a linear actuator and servo vs stepper.

Laboratory equipment that is not a medical device is normally assessed to IEC 61010-1 rather than IEC 60601-1. Confirm the classification first, because it sets the insulation levels your motors and drives need.

Cleanrooms, cleaning and environment

Where the instrument goes into a controlled room, the customer will quote an ISO 14644-1 class. Class 5, for example, allows 3,520 particles/m³ at 0.5 µm and above. Brush slip rings, exposed ball screws and greased guides are all particle sources. Ask for sealed or shielded versions, cleanroom grease, and test data if the supplier has it.

Also confirm:

• Cleaning agents: alcohols, peroxide vapour and chlorine-based wipes attack some plastics, cable jackets and anodising
• Audible noise: give a dB(A) target at a stated distance, and remember that drive PWM frequency and stepper resonance are common sources of whine
• EMC: motors and drives near sensitive detectors or ECG front-ends need shielded cables and filtered drives
• Ingress: spills on lab decks justify IP54 or better on exposed axes

Common mistakes

• Asking a supplier for a “60601-certified motor” instead of the insulation, creepage and test data the device file actually needs
• Choosing iron-core linear motors for slow dispensing moves, then fighting cogging in the control loop
• Ignoring holding behaviour on vertical axes and surgical arms: no brake, no safe state
• Leaving out data-link hardware when checking the CT ring envelope
• Approving a part without change-notification terms, then finding the supplier changed a material after verification

What to send us

Send the axis type and what it moves, the stroke or rotation, the load, speed, accuracy and duty. Add the voltage available, the safety standard the device is assessed to (IEC 60601-1 or IEC 61010-1), any cleanroom class, and your noise target. For slip rings, list every circuit with its current, voltage and signal type, plus the bore, envelope and speed. Our specialist engineering and supply partners will come back with a proposal you can take into your design review.

Standards to have in view

• IEC 60601-1 (medical electrical equipment, basic safety and essential performance)
• IEC 60601-1-2 (EMC for medical electrical equipment)
• IEC 60601-2-44 (CT X-ray equipment)
• IEC 80601-2-77 (robotically assisted surgical equipment)
• IEC 61010-1 (laboratory equipment safety)
• ISO 13485 (medical device quality management)
• ISO 14971 (medical device risk management)
• ISO 14644-1 (cleanroom air cleanliness classes)

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