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A Comprehensive Guide to Measure the Performance of Joints in Humanoid Robots

Like people need to maintain healthy joints, robots require strong and accurate joints to enhance their performance and capabilities. This notion might seem simple at first glance, yet designing the ideal joint for a robot is a complex task—nonetheless, it’s crucial. For humanoid robots, having durable joints is not only a matter of performance but also of safety. The question then arises: by what standards do we gauge the performance of these robotic joints?  

This article will take you through the ins and outs of measuring robotic joint performance. We’ll look at the tools needed, the challenges faced, and how technology can help us improve these crucial metrics.

Key Performance Metrics for Measuring Joint Performance

Before diving into the measurement techniques, it’s crucial to understand what the key metrics are to measure the performance of a humanoid robot joint. Those metrics can vary depending on the specific application and requirements of the system. However, some common key performance metrics include:

  1. Range of Motion (ROM) – unit degrees (°): This metric assesses the maximum angle through which a joint can move.
  2. Payload Capacity – unit kilograms (kg): Payload capacity refers to the maximum weight that the joint can support or manipulate.
  3. Torque–unit newton-meters (Nm): The ability of a joint to apply force is measured in torque. High torque values are indicative of a joint’s strength and its ability to handle heavy loads or resist external forces.
  4. Stiffness – unit Newtons-meter per arc.min (Nm/arcmin): Stiffness measures the resistance of the joint to deformation or deflection under load.
  5. Speed and Acceleration in linear motion – unit meters per second (m/s) for speed, and meters per second squared (m/s²) for acceleration: These metrics evaluate how fast a joint can move and how quickly it can reach its maximum speed, respectively. Note: for rotational movement, the unit is rad/s or RPM ( revolution per minute).
  6. Response Time – unit milliseconds (ms): Response time measures how quickly the joint can react to control signals or commands.
  7. Accuracy and Precision – unit usually measured in millimeters (mm) or micrometers (µm): These factors measure a joint’s ability to reach a desired position or follow a specific path with minimal deviation.
  8. Responsiveness – unit seconds (s) or milliseconds (ms): Overall quality and efficiency with which a system or service reacts to user inputs, encompassing both speed and effectiveness. It includes user perception of how quickly and smoothly interactions are handled.
  9. Repeatability in motion – unit measurement of distance and/or angle: Measures the consistency of a joint’s movements when it repeats the same task or motion multiple times. It is typically quantified by the variation in position achieved during repeated executions of the same motion.
  10. Noise Levels – unit decibels (dB): Noise levels assess the amount of sound generated by the joint during operation.
  11. Energy Efficiency – units % as the result of the ratio between the energy required to do a task/total energy spent: Energy efficiency measures the amount of energy consumed by the joint to perform its tasks.
  12. Durability – unit cycles or hours of operation: Durability refers to the ability of the joint to withstand repeated use over time without experiencing mechanical failures or degradation in performance. It is typically measured in terms of the number of cycles or hours of operation before maintenance or replacement is required.

Techniques for Measuring Joint Performance

Evaluating the functionality of robotic joints can be conducted through two primary approaches: simulation-based and real-world-based testing.

  • Simulation & Modeling: This approach utilizes software to create virtual models and scenarios for the joint, presenting advantages in safety, convenience, and cost savings. Despite these benefits, it’s important to note that simulation and modeling can lead to greater inaccuracies, uncertainties, and constraints due to your model limitations. Should the simulation yield positive outcomes, engineers then move forward with the physical construction and testing of the robotic arm.

If the simulation shows a satisfactory result, engineers then proceed to the physical implementation of the robotic arm and its tests. [.]

  • Real-World-Based Testing: Contrarily, this method employs tangible platforms and setups to test the joint ensuring a higher degree of realism, authenticity, and direct feedback. While providing valuable insights, this approach comes with increased risks, challenges, and financial implications.

Tools and techniques for real-world-based testing method

Here is a list of real-world-based testing methods. For each of the testing methods mentioned, specific tools and techniques are employed to assess the performance of robotic joints effectively:

a. Torque Analysis:

Tools Used: Torque sensors or torque meters.

Purpose: These devices are instrumental in measuring the torque and force exerted by a robotic joint. The accurate torque measurements they provide are crucial for assessing a joint’s strength and ability to handle loads, making them essential for evaluating mechanical performance and endurance.

b. 3D Motion Tracking Systems:

Tools Used: Cameras or specialized motion capture systems.

Purpose: These systems capture and analyze the movement of robotic joints in real-time, offering detailed insights into the joint’s range of motion, speed, and precision of its movements. By recording the movement in three dimensions, motion capture systems are invaluable for understanding dynamic performance and improving the accuracy of robotic systems.

c. Angular Movement Analyzers:

Tools Used: Rotary encoder.

Purpose: These devices are designed to measure the angles at which joints move, providing accurate data on a joint’s range of motion.

d. Stiffness Analysis:

Tools Used: Mechanical testing machines built with several components (torque sensors, encoders, and linear displacement measurement…).

Purpose: These tools perform mechanical tests to determine the joint’s stiffness, its ability to resist deformation, and its response to various loads.

e. Control System Analysis:

Tools Used: Oscilloscopes, signal analyzers, and specialized control software.

Purpose: These instruments and software analyze the performance of the joint’s control system by monitoring control signals, feedback loops, and the effectiveness of closed-loop control systems. The goal is to refine the joint’s control algorithms and parameter settings for optimal performance.

f. Energy Consumption Analysis:

Tools Used: Energy meters and data logging equipment.

Purpose: These devices measure the energy consumed by the robotic joint during its operation. Analyzing energy consumption data over time aids in evaluating the joint’s energy efficiency and in pinpointing areas where energy usage can be optimized.

Challenges in Measuring Joint Performance

Measuring the performance of robotic joints involves complex processes and technologies. These challenges are pivotal not only in accurately assessing joint capabilities but also in ensuring the overall efficacy and reliability of robotic systems. Here, we delve into some of the primary hurdles encountered in the measurement of joint performance:

a. Precision and Accuracy:

Factors such as sensor calibration, environmental conditions, and the inherent limitations of measurement tools can introduce errors. For instance, torque sensors must be meticulously calibrated to ensure that the force exerted by joints is measured accurately, without external influences skewing the data.

b. Dynamic vs. Static Conditions:

Dynamometers and torque sensors excel in static measurements, but accurately assessing dynamic performance, especially under rapid movement or changing loads, poses significant challenges and requires sophisticated testing setups.

c. Complex Motion Patterns:

Motion capture systems offer a solution by tracking movement in three-dimensional space, yet the complexity of data analysis increases exponentially with the intricacy of the joint’s motion. This necessitates advanced algorithms and software to accurately interpret the vast amounts of data generated.

d. Environmental Interference:

External environmental factors such as temperature, humidity, and electromagnetic interference can affect measurement accuracy. Sensors and electronic devices are susceptible to such interferences, which can distort the data collected.

e. Wear and Longevity Testing:

Assessing the long-term performance and wear of robotic joints requires prolonged testing periods, simulating years of operation within a short timeframe. This presents logistical challenges, including the time and resources needed to conduct such extensive tests.

f. Integrating Measurement Tools:

Incorporating measurement tools directly into the robotic joints without impacting their performance is a delicate balance. The added weight or alteration in the joint structure can influence its natural behavior, thereby affecting the reliability of the performance data collected.

g. Data Interpretation and Application:

Lastly, translating the raw data collected from tests into actionable insights presents its own set of challenges. Engineers must sift through extensive datasets to identify patterns, anomalies, and performance benchmarks. Problems that for instance those researchers were facing when trying to get a better method to measure lost motion. 

Improving robotic joint key performance with the Archimedes Drive

Incorporating the Archimedes Drive into robotic joints can markedly enhance their performance across several key metrics. This innovative drive technology addresses common challenges faced in robotic applications, such as efficiency, precision, noise levels, and durability:

  • Optimal use of Power – Efficiency

The Archimedes Drive boasts an efficiency rate of over 85–95%, primarily due to its design that minimizes friction losses. This efficiency is crucial for robotic applications where energy conservation and optimal use of power are paramount. The drive’s design ensures that more input energy is converted into useful work, improving the overall energy efficiency of the robotic system.

  • Precise movement – Precision and Accuracy

One of the most significant benefits of the Archimedes Drive is its ability to achieve true zero backlash​. Backlash can lead to inaccuracies in movement and positioning. The Archimedes Drive’s unique traction mechanism ensures precise movement control, making it especially suitable for applications requiring high levels of accuracy and repeatability.

  • Enhanced reliability – Durability

The Archimedes Drive’s design inherently protects against overtorque situations, which can cause significant damage to traditional gear systems. By evenly distributing loads and utilizing a mechanism that allows for microslip under extreme stress, the Archimedes Drive can handle sudden and unexpected increases in load without suffering catastrophic failure.

  • Improved Working Environments – Noise levels

The Archimedes Drive operates at significantly lower noise levels—under 50 dB in many cases—making it one of the quietest drives available. This reduction in noise is beneficial for the comfort and safety of human operators working near robots and complies with increasingly stringent regulations regarding workplace noise levels.

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The Archimedes Drive is a groundbreaking technology that surpasses traditional speed reducers in performance, precision, and efficiency. Discover how our innovative design revolutionizes the industry and brings unparalleled advantages to your applications.