Robot temperature rise testing is a critical safety and performance evaluation that measures how much key components, such as servo motors, reducers, joint modules, controllers, and operator-accessible surfaces, heat up relative to ambient conditions during operation. Conducted in accordance with recognized standards from ISO, IEC, GB, EN, UL, ASTM, and JIS, these tests verify insulation integrity, lubricant stability, electronic component reliability, and human-contact safety before robots enter service. This guide explains the sample types, test items, measurement methods, acceptance criteria, and practical applications of robot temperature rise testing.
Technical Overview
Temperature rise testing quantifies the difference between the temperature of a robot component and the ambient (cooling medium) temperature under defined operating conditions. Expressed in kelvin (K), temperature rise isolates the heat generated by the machine itself from environmental influence, allowing objective comparison against thermal limits specified in product standards.
Excessive heating in robots accelerates insulation aging in motor windings, degrades lubricants inside harmonic and cycloidal reducers, induces thermal expansion and positional error in precision drivetrains, shifts encoder and sensor calibration, and can create burn hazards on surfaces touched by operators. For collaborative robots, hot external surfaces are a direct functional-safety concern because humans share the workspace with the machine.
The principal heat sources evaluated in a typical robot include I2R losses in motor windings, iron losses in magnetic cores, friction and churning losses in gear reducers, switching and conduction losses in servo drives, energy dissipated in brake resistors and regenerative circuits, and internal resistance losses in batteries of mobile platforms.
The applicable standards framework draws on ISO 10218-1 and ISO 10218-2 for industrial robots, ISO/TS 15066 for collaborative robot applications, ISO 13482 for personal care robots, IEC 60034-1 for rotating electrical machines, IEC 61800-5-1 for adjustable-speed power drive systems, IEC 62368-1 for electronic controllers, and IEC 62133-2 for battery packs. Chinese national standards include GB 11291.1, GB/T 36008, GB 4943.1, and the GB/T 2423 series, while EN adoptions of the IEC and ISO documents apply in Europe, UL 1740 and UL 62368-1 apply in North America, and the JIS C 60068 series provides corresponding Japanese environmental test methods.
Testing Samples
Joint Modules, Servo Motors, and Reducers
Individual servo motors, harmonic wave gear and RV or cycloidal reducers, electromagnetic brake assemblies, and integrated smart joint modules are tested on dynamometer benches or as installed in the arm, reproducing rated torque, speed, and reversals.
Complete Manipulators
Articulated six-axis arms, SCARA, delta, and cartesian robots are tested as complete systems while executing representative motion programs at rated payload, rated speed, and specified duty cycle until thermal equilibrium is reached.
Collaborative Robots
Cobot arms, grippers, force-torque sensors, and end effectors are evaluated with particular attention to external surface temperature, because these surfaces may contact operators during collaborative tasks.
Mobile Robots and Battery Systems
AGV and AMR drive units, wheel hub motors, lithium-ion battery packs, onboard chargers, and docking contacts are tested under sustained transport missions and charge-discharge profiles.
Controllers and Power Electronics
Robot controllers, servo drive cabinets, switch-mode power supplies, transformers, brake resistors, DC bus capacitors, terminal blocks, and internal wiring are assessed under maximum continuous load and worst-case regenerative conditions.
Service and Humanoid Robots
Actuator modules, control units, and external enclosures of household, educational, medical assistance, and humanoid robots are evaluated where prolonged human contact is foreseeable.
Testing Items
Typical temperature rise test items for robotic systems include:
- Steady-state winding temperature rise of servo and stepper motors determined by the resistance method
- Surface temperature rise of reducer housings, flanges, bearings, and joint casings
- Temperature rise of controller power semiconductors, electrolytic capacitors, magnetics, and PCB hot spots
- Touch temperature of accessible surfaces including arm covers, grippers, teach pendants, and housings
- Temperature rise under overload, stall, and locked-rotor conditions
- Thermal behavior across duty types S1 through S10 as defined in IEC 60034-1
- Brake resistor and regenerative circuit temperature under repeated deceleration cycles
- Battery pack and charging system temperature during rated and fast charging
- Lubricant and internal oil temperature inside sealed gearboxes
- Verification of thermal protection devices such as PTC sensors, thermostats, and temperature-controlled fans
- Heat runs at elevated ambient temperature, for example 40°C, to establish derating curves
Testing Methods
Test Conditions and Load Profiles
Tests are performed in an ambient-controlled room or climatic chamber, typically at 20°C ± 5°C unless otherwise specified, with airflow consistent with the intended cooling arrangement. The robot operates at rated voltage and frequency under a defined payload and motion program, or the drive train is loaded by dynamometer. Continuous duty (S1) is the baseline profile; intermittent duty cycles are applied when they represent real service.
Thermocouple Method
Type K or type T thermocouples are bonded to measurement points using high-thermal-conductivity adhesive or welded junctions. Sensor locations are selected after infrared screening of the hottest regions. Multi-channel data loggers record temperatures continuously until stable readings are obtained, with junctions electrically insulated where surface potentials exist.
Resistance Method for Windings
Because winding hot spots are inaccessible to contact sensors, temperature rise is calculated from resistance change. The cold resistance R1 is measured at known winding temperature t1, the machine runs to thermal equilibrium, and the hot resistance R2 is captured immediately at shutdown. The temperature rise is calculated as: Δt = (R2 − R1) / R1 × (k + t1) + (t1 − t2), where k equals 235 for copper and 225 for aluminum, and t2 is the ambient temperature at the end of the test. When the ambient differs from the 40°C reference coolant temperature, the result is corrected in accordance with IEC 60034-1.
Infrared Thermography
Radiometric infrared cameras, applied in line with ASTM E1934 practice for thermographic inspection of electrical and mechanical equipment, are used to survey surfaces, locate hot spots, and confirm thermocouple placement. Emissivity is corrected using tape or paint of known emissivity. Thermography supports the assessment but compliance values are normally confirmed by contact sensors or the resistance method.
Determination of Thermal Equilibrium
A test continues until thermal equilibrium is reached, commonly evidenced by a rate of temperature change of no more than 1 K per hour at all monitored points, or as specified in the relevant standard. Practical test durations range from two to eight hours depending on thermal mass and duty cycle. Where shutdown delay affects hot resistance readings, correction or extrapolation procedures permitted by the standard are applied.
Acceptance Criteria and Limits
Winding temperature rise limits by resistance method with 40°C reference coolant follow the insulation class limits of IEC 60034-1: 60 K for Class A, 75 K for Class E, 80 K for Class B, 105 K for Class F, and 125 K for Class H. Electronic components are assessed against their own ratings and the safeguards of IEC 62368-1 and IEC 61800-5-1. Touch temperatures are evaluated against ISO/TS 15066 and IEC 62368-1, which relate permissible contact temperature to contact duration and material; prolonged contact with bare metal surfaces is generally limited to roughly 43°C to 48°C, with higher values permitted for shorter contact times and lower-conductivity materials. Gearbox lubricant temperatures are typically restricted to about 80°C to 90°C depending on the oil type.
Applications
Robot temperature rise testing supports engineering decisions and regulatory compliance throughout the product life cycle:
- Design validation and correlation of thermal simulation models with measured hardware behavior
- Compliance testing supporting CE marking, CB Scheme certification, and North American listings under UL 1740
- Safety verification of collaborative applications where operator contact with the robot is foreseeable
- Reliability engineering, including insulation life estimation based on thermal aging models
- Derating determination, defining permissible payload and speed envelopes at elevated ambient temperatures
- Production quality control and verification of design changes, replacement components, or firmware updates
- Benchmarking of thermal performance across motor, reducer, and drive supplier options
FAQ
What is the difference between temperature and temperature rise?
Temperature is the absolute value measured at a point, while temperature rise is the component temperature minus the ambient temperature during the test. Expressing results as temperature rise in kelvin allows fair comparison of machines tested in different environments and aligns with the limit tables in IEC and GB standards.
How long does a robot temperature rise test take?
A steady-state heat run typically lasts two to eight hours, depending on the thermal mass of the robot and the duty cycle. The test ends only when all monitored points reach thermal equilibrium, usually defined as a change of no more than 1 K per hour.
Which standards govern robot temperature rise testing?
There is no single universal standard; the applicable documents depend on the component and market. Motors follow IEC 60034-1, drives follow IEC 61800-5-1, controllers follow IEC 62368-1 or GB 4943.1, robot safety follows ISO 10218-1 and GB 11291.1, collaborative robots follow ISO/TS 15066 and GB/T 36008, batteries follow IEC 62133-2, and environmental conditioning follows the IEC 60068 and GB/T 2423 series.
Why is the resistance method used for motor windings?
The hottest region of a winding is buried inside the slot and cannot be reached by a surface sensor. The resistance method converts the increase in copper resistance into an average winding temperature rise, providing a repeatable, standards-recognized figure without disturbing the machine.
Are surface temperature limits stricter for collaborative robots?
Yes. In collaborative applications, contact between the operator and the robot is expected rather than excluded, so ISO/TS 15066 applies pain-threshold-based limits that depend on contact duration and surface material. Metal surfaces under prolonged contact face the strictest values, often below 50°C.
Can testing be performed at high ambient temperatures?
Yes. Heat runs inside a climatic chamber at elevated ambient, such as 35°C or 40°C, are used to establish derating curves and verify that the robot maintains compliance in hot industrial environments. Results may be corrected to the 40°C reference coolant temperature defined in IEC 60034-1.
Is an accredited third-party laboratory required?
Accredited third-party laboratories are generally required for certification-related temperature rise tests that support market access, since notified bodies and certification schemes demand traceable instrumentation and witnessed procedures. Internal laboratory testing remains valuable for development iterations and design verification before formal submission.