Retention Accuracy Testing Service – Comprehensive Evaluation of Positional Stability, Backlash and Repeatability for Actuators, Joints and Precision Mechanical Systems
As an ISO/IEC 17025 accredited independent testing laboratory, we offer specialised retention accuracy testing services to manufacturers, engineering contractors, and quality assurance teams across the automotive, aerospace, robotics, medical device, industrial automation, and precision engineering sectors. Retention accuracy – the ability of a positioning system, actuator, joint, or mechanical assembly to maintain its intended position or return to a specified reference point after displacement, loading, or external disturbance – is a critical performance parameter for applications where precision and reliability are paramount. Our test protocols evaluate the positional stability, backlash, hysteresis, repeatability, and long‑term drift of a wide range of components and systems under controlled and simulated service conditions. All methods are aligned with ISO, IEC, ASTM, and GB/T standards, including ISO 230‑2 (Machine tools – Determination of accuracy and repeatability of positioning), IEC 60034‑2‑1 (Rotating electrical machines – Efficiency measurement), ASTM E2309 (Digital data acquisition), GB/T 17421 (Machine tools – Test code for positioning accuracy), and GB/T 11365 (Measurement of backlash). Our inspection and test reports are recognised by the National Medical Products Administration (NMPA), the State Administration for Market Regulation (SAMR), the Ministry of Industry and Information Technology (MIIT), and international certification bodies for product registration, type approval, and quality assurance.
Components and Systems We Regularly Test
Our retention accuracy test facilities accommodate a wide range of positioning and mechanical systems. Typical test articles include:
- Linear actuators and positioning stages – electric, pneumatic, and hydraulic linear actuators with ball screws, lead screws, and linear motors
- Rotary actuators and servo motors – for precise angular positioning and indexing applications
- Robotic arms and articulated joints – for assessing the positional repeatability and backlash of each joint
- Medical devices and surgical instruments – for precision positioning and motion control in minimally invasive surgery
- Automotive components – steering columns, suspension components, and seat adjusters
- Aerospace actuators and flight control surfaces – for assessing the positional stability under vibration and load
- Precision tooling and clamping systems – for assessing the holding accuracy and repeatability of tool holders and workholding devices
- Gearboxes and transmission systems – for measuring backlash, hysteresis, and torsional stiffness
Positional Accuracy and Repeatability Testing – Assessing the Static and Dynamic Positioning Performance
- Positional accuracy and repeatability measurement – ISO 230‑2 / GB/T 17421 – for linear and rotary axes – We measure the positional accuracy (the difference between the commanded position and the actual position) and the repeatability (the scatter of the actual positions) of the test article using a high‑precision laser interferometer (accuracy ±0.1 µm) or a high‑resolution linear encoder (resolution 0.1 µm). The test is performed over the full travel range (for linear axes) or over the full rotation range (for rotary axes). The measured positions are recorded at multiple target positions (typically 5‑10 points per axis). The accuracy is expressed as the maximum error (in µm or arc‑seconds), and the repeatability is expressed as the standard deviation (or the 2σ value) of the position errors.
- Bi‑directional positioning testing – for assessing the forward and reverse positioning performance – We measure the positional accuracy and repeatability in both the forward (increasing position) and the reverse (decreasing position) directions. The bi‑directional error (the difference between the forward and reverse positions) is calculated and used to assess the backlash and the hysteresis of the system.
- Backlash measurement – ISO 230‑2 / GB/T 17421 – for assessing the free play in the transmission system – We measure the backlash (the free play or lost motion) of the system by applying a small displacement in the forward direction, recording the position, and then applying a small displacement in the reverse direction. The difference between the two positions is the backlash (in µm or arc‑seconds). A low backlash (< 50 µm for linear axes, < 10 arc‑seconds for rotary axes) is required for high‑precision applications.
- Hysteresis measurement – for assessing the elastic and frictional effects – We measure the hysteresis (the difference between the forward and reverse paths) by recording the position as a function of the load (or the force) during a complete loading‑unloading cycle. The hysteresis is expressed as a percentage of the full‑scale range.
Retention Accuracy Under Load – Assessing Positional Stability Under Static and Dynamic Loading
- Static load retention test – for assessing the positional change under a sustained load – We apply a specified static load (tension, compression, or torque) to the test article and measure the change in position (or the drift) over a specified period (typically 1‑24 hours). The load is applied using a calibrated force actuator (or a dead weight), and the position is measured using a high‑precision displacement sensor (accuracy ±0.1 µm). The maximum position change (in µm) and the drift rate (in µm/hour) are reported.
- Dynamic load retention test – for assessing the positional stability under cyclic loading – We apply a cyclic load (sinusoidal or block‑cycle) to the test article and measure the position variation during the loading cycle. The test is performed at a specified frequency (typically 0.1‑10 Hz) and a specified load amplitude. The position variation (in µm) is reported as the peak‑to‑peak error.
- Step response and settling time – for assessing the dynamic response of the positioning system – We apply a step command (a sudden change in the target position) and measure the time taken for the system to reach the target position (the settling time) and the overshoot (the maximum position error). The test is performed at multiple step amplitudes and at the specified load condition.
- Position drift under thermal load – for assessing the effect of temperature on the positional stability – We condition the test article at a specified temperature (e.g., 20 °C, 40 °C, 60 °C) and then measure the position drift (the change in position over time) at that temperature. The test is performed for a specified period (e.g., 1‑4 hours). The position drift (in µm/°C or µm/hour) is reported.
Environmental and Durability Testing – Simulating Service Conditions
- Temperature‑conditioned retention accuracy test – for assessing the effect of temperature on the positional stability – We perform the retention accuracy test at elevated temperatures (e.g., 40 °C, 60 °C, 80 °C) and at reduced temperatures (e.g., -20 °C, -40 °C) using a temperature‑controlled chamber. The test assesses the effect of thermal expansion and contraction on the positional accuracy, backlash, and repeatability.
- Humidity‑conditioned retention accuracy test – for assessing the effect of moisture on the positional stability – We condition the test article in a high‑humidity environment (e.g., 95 % RH, 40 °C) for a specified period (e.g., 168 hours) and then perform the retention accuracy test. The test assesses the effect of moisture on the position sensors, the lubricants, and the mechanical components.
- Vibration and shock testing – IEC 60068‑2‑6 / GB/T 2423.10 – for assessing the positional stability under dynamic loading – We subject the test article to a defined vibration profile (sinusoidal or random) and then perform the retention accuracy test. The test assesses the effect of vibration on the positional accuracy, backlash, and repeatability.
- Salt spray and corrosion testing – ASTM B117 / ISO 9227 / GB/T 10125 – for coastal and marine applications – We expose the test article to a salt spray environment (5 % NaCl, 35 °C) for 240‑500 hours and then perform the retention accuracy test. The test assesses the effect of corrosion on the positional stability and the mechanical integrity.
- Thermal cycling and ageing – for assessing the long‑term positional stability – We subject the test article to a specified number of thermal cycles (e.g., 50‑100 cycles between -40 °C and +80 °C) and then perform the retention accuracy test. The test assesses the effect of thermal fatigue on the positional stability, the backlash, and the repeatability.
Data Analysis and Interpretation – Quantifying Retention Accuracy
- Positional accuracy – the maximum deviation from the commanded position – The positional accuracy (in µm or arc‑seconds) is the maximum difference between the commanded position and the actual position over the full travel range. A low positional accuracy (< 10 µm for linear axes, < 5 arc‑seconds for rotary axes) is required for high‑precision applications.
- Repeatability – the scatter of the position errors – The repeatability (in µm or arc‑seconds) is the standard deviation (or the 2σ value) of the position errors at a given target position. A low repeatability (< 5 µm for linear axes, < 2 arc‑seconds for rotary axes) is required for applications requiring high consistency.
- Backlash – the free play in the transmission system – The backlash (in µm or arc‑seconds) is the difference between the forward and reverse positions at a given target position. A low backlash (< 50 µm for linear axes, < 10 arc‑seconds for rotary axes) is required for high‑precision applications.
- Hysteresis – the elastic and frictional effects – The hysteresis (in µm or arc‑seconds) is the difference between the forward and reverse paths during a complete loading‑unloading cycle. A low hysteresis (< 20 µm for linear axes, < 5 arc‑seconds for rotary axes) is required for precise positioning.
- Statistical analysis – for batch‑to‑batch consistency and process capability – For multiple test articles, we report the mean accuracy, the mean repeatability, the mean backlash, and the standard deviation. A coefficient of variation (CV) of < 10 % is considered acceptable for most applications.
Regulatory Compliance and Product Certification – Supporting Industry Standards
Our retention accuracy testing services are performed in accordance with the most widely used international and national standards. The most commonly requested include:
- ISO 230‑2 – Machine tools – Determination of accuracy and repeatability of positioning of numerically controlled axes – the primary standard for positioning accuracy and repeatability
- GB/T 17421 – Machine tools – Test code for positioning accuracy – the Chinese national standard for positioning accuracy
- IEC 60034‑2‑1 – Rotating electrical machines – Efficiency measurement – for electrical machine testing (used as a reference)
- ASTM E2309 – Standard Practice for Digital Data Acquisition – for data acquisition and analysis
- GB/T 11365 – Measurement of backlash – the Chinese national standard for backlash measurement
- ISO 9283 – Manipulating industrial robots – Performance criteria and related test methods – for robot positioning performance
- GB/T 12642 – Performance criteria and related test methods for industrial robots – the Chinese national standard for robot performance
- ISO 230‑1 – Machine tools – Test code for machine tools – Part 1: Geometric accuracy – for geometric accuracy
Report Acceptance and Regulatory Recognition
All retention accuracy tests are conducted under our ISO/IEC 17025 accreditation, using calibrated laser interferometers, linear encoders, load cells, and environmental chambers, all traceable to national and international reference standards. Our final test reports include: a complete description of the test article (type, specifications, manufacturer), the test method and conditions (temperature, humidity, load, travel range), the measured parameters (positional accuracy, repeatability, backlash, hysteresis, drift), a statistical summary (mean, standard deviation, coefficient of variation), and a clear pass/fail verdict against your specified acceptance criteria. These reports are accepted by the National Medical Products Administration (NMPA), the State Administration for Market Regulation (SAMR), the Ministry of Industry and Information Technology (MIIT), and international certification bodies for product registration, type approval, and quality assurance. Bilingual (English/Chinese) versions are available to facilitate submissions to domestic and international authorities and to support your global market access.
