Flat-Linear Hysteresis Curve Achieved Through True Zero Backlash and High Stiffness in the Archimedes Drive
Abstract
Minimizing backlash is essential for achieving high accuracy in motion control systems. Despite claims of ‘zero backlash,’ many conventional drives exhibit mechanical play, compromising precision. This paper explores the impact of backlash on motion accuracy and presents the Archimedes Drive as a solution that maintains true zero backlash through continuous contact between components. We examine how the drive ensures constant rigidity, minimizes lost motion, and maintains precision over its operational lifetime.
Introduction
Backlash, or mechanical play between mating components, negatively impacts motion accuracy and repeatability. Traditional drive systems compensate for backlash through error corrections, introducing latency and reducing efficiency. The Archimedes Drive eliminates backlash entirely by maintaining continuous contact between its components, resulting in superior motion accuracy without compensation requirements. The Archimedes Drive is a compound planetary traction drive, which relies on smooth rolling surfaces instead of gear teeth. All core components are made from steel.
A ) Backlash and Its Impact on Accuracy :
1 – Definition of Backlash :
Backlash refers to the mechanical gap between engaged components, allowing unintended movement when switching direction. It is commonly found in gear-based systems and results in positional errors that require compensation.
Backlash=(Maximum Deflection)−(Minimum Deflection) at 0Nm of Torque.
System movement (W) under system load (P) is a cumulative function of each component stiffness (K_n) supporting the load.
>> The system stiffness is determined by the combined stiffness of the interconnected mechanical components
2 – Accuracy in Load Direction Switching :
In conventional systems, backlash introduces positional errors that require computational compensation, which slows response time. The Archimedes Drive, by eliminating backlash, enables immediate and precise motion adjustments, enhancing both speed and accuracy.
3 – Accuracy in End-Position Precision:
Traditional robotic systems must perform stepwise corrections near target positions due to backlash-related errors. The Archimedes Drive eliminates these corrections, allowing direct and accurate positioning, reducing cycle times, and increasing efficiency in high-speed applications.
B ) Lost Motion and Its Effect on Accuracy
1 – Definition of Lost Motion :
Lost motion refers to the deviation between the intended and actual output positions, primarily caused by backlash and torsional deflection. It is quantified as the positional deviation at ±3% of nominal torque, serving as a critical performance metric in precision applications.
It is important to note that this definition pertains specifically to the lost motion within the drive itself. The total lost motion of a complete system also includes contributions from other components, such as bearings, joints, and the end-effector.
Figure 1: Hysteresis Curve Strain Wave Gear vs Flat-Linear Hysteresis Archimedes Drive
2 – Minimization of Lost Motion in the Archimedes Drive :
The Archimedes Drive reduces lost motion through its zero-backlash design and high torsional stiffness. By ensuring preloaded rolling contact, it prevents localized stress and deformation, resulting in minimal lost motion.
C ) Structural Features Enhancing Accuracy
1 – Component Disposition :
The Archimedes Drive maintains true zero backlash by tightly clamping steel Flexrollers (planets) between the structural components. This eliminates mechanical gaps and ensures constant contact under all operating conditions.
2 – High Torsional Stiffness :
A fundamental advantage of the Archimedes Drive is its high structural stiffness, achieved through optimized bearing integration and load distribution. This design inherently resists positional deviation caused by external forces, ensuring that accuracy is maintained even under variable loads. As a result, the system delivers reliable performance in applications requiring sustained precision.
Figure 2: Archimedes Drive core components.
3 – Wear Resistance and Long-Term Precision :
The preloaded design of the Archimedes Drive prevents backlash development due to wear. Flexrollers maintain contact even as material wear occurs, preserving accuracy and minimizing performance degradation over time.
Figure 3: Over exaggerating elastic expansion of the steel Flexrollers (planets) during wear.
Conclusion:
Backlash is a fundamental challenge in high-precision motion control, limiting accuracy and efficiency. Traditional drives rely on compensation mechanisms that introduce delays and reduce performance. The Archimedes Drive, through its innovative zero-backlash design, eliminates the need for compensation, ensuring continuous accuracy and high stiffness. By distributing forces evenly and maintaining a preloaded configuration, the Archimedes Drive offers unparalleled precision, making it the ideal choice for robotics and other high-accuracy applications.
