Sources of Positional Error in Industrial and Collaborative Robot Arms — and How to Reduce Them

The problem

Robot manufacturers specify repeatability — the ability to return to the same taught point — which is typically ±0.02–0.1 mm for industrial arms and ±0.03–0.1 mm for cobots. Accuracy — the ability to reach an arbitrary commanded position — is significantly worse: ±0.5–1.5 mm or more, depending on the platform, configuration, payload, and thermal state.

This 10× gap between repeatability and accuracy exists because repeatability only requires consistent servo behavior, while accuracy depends on the kinematic model matching the physical arm. Sources of positional error include:

Kinematic parameter errors: Manufacturing tolerances in link lengths, joint offsets, and axis alignment cause the nominal DH (Denavit-Hartenberg) parameters to diverge from the physical arm. These are fixed per unit but vary between robots of the same model.
Joint-level tracking errors: Compliance in gearboxes, belts, and bearings means the actual joint angle differs from the commanded angle, especially under load or during dynamic motion.
Thermal drift: Steel arm segments expand approximately 12 µm/m/°C. A 2-meter-reach arm experiencing a 30°C temperature change can drift ~1 mm over the course of a shift.
Gravitational deflection: Payload and arm self-weight cause elastic deformation that varies with configuration.

Conventional mitigations focus on one source at a time. Kinematic calibration corrects the kinematic model. Laser tracker measurement provides ground-truth position data. OEM accuracy packages (where available) are platform-specific and typically limited to one model family.

How software-based accuracy improvement works

Two complementary approaches address different error sources:

Kinematic calibration identifies the actual kinematic parameters of a specific arm — correcting the nominal DH model to match the physical robot. This is done through a calibration procedure that measures the arm's position at multiple configurations and solves for the parameter errors. Once the corrected model is loaded, all commanded positions are more accurate. Recent research (Nature Communications Engineering, 2026) demonstrated reducing errors from ~10 mm to 0.2 mm on Franka, KUKA, and Kinova cobots using kinematic calibration alone.

Dynamic joint tracking addresses real-time joint-level errors — the compliance and backlash that cause the actual joint angle to differ from the commanded angle. By modeling and compensating for these effects in real time, the robot's executed trajectory more closely matches the intended trajectory.

Neither approach requires permanent sensors, controller firmware changes, or mechanical modification to the robot.

Performance

Up to 5.7x TCP accuracy improvement demonstrated on collaborative robot platforms
Kinematic calibration can reduce positional error from millimeters to sub-millimeter
Dynamic joint tracking addresses errors that persist after kinematic calibration — particularly under payload and during motion
Combined approach addresses both static (kinematic) and dynamic (compliance, thermal) error sources

Integration

Software-based — operates through the robot's existing command interface
Kinematic calibration requires a measurement procedure (accelerometer or external reference) but no permanent instrumentation
Joint tracking runs in real time between the trajectory planner and the robot SDK
Currently supported on Standard Bots, UFACTORY, Trossen, and Denso platforms
Cloud API for model identification; local runtime for real-time compensation

Business context

Accuracy limitations restrict the applications a robot can serve. A cobot with ±0.03 mm repeatability but ±1 mm accuracy cannot reliably perform tasks requiring sub-millimeter positioning — offline-programmed paths, multi-robot coordination, or precision assembly — without extensive touch-up. Improving accuracy through software expands the application range of existing hardware and reduces the integration effort for accuracy-sensitive tasks.