Hollow rotary tables have become the core rotary motion units in industrial automation, robot joints, precision measurement and semiconductor equipment due to their hollow structure design, excellent load carrying capacity, smooth power transmission, and standard accuracy of up to 15 arc seconds (customized models up to 10 arc seconds).Its excellent performance comes from the precise composition of components and rigorous design and manufacturing process.
1. Core components of hollow rotary platform
(1) Precision spindle:
As the core support and load transfer hub of the platform, the spindle is usually made of high-strength alloy steel (e.g. SCM440) by integral forging or precision casting, and undergoes rigorous carburizing and quenching and other heat treatment processes to ensure that it has a high surface hardness of HRC 58-62 as well as excellent core toughness.Key mating surfaces (e.g. bearing mounting bits) need to be precision ground, roundness error is strictly controlled within 5 microns (μm) or even lower (e.g. <2μm) to provide a stable foundation of high rigidity and low deformation, which is directly related to the platform's loading capacity and long-term accuracy retention.
2) High rigidity crossed roller bearings:
This is the core of realizing high precision (15/10 arc sec) and high rigidity of the platform.Its unique design is that the rollers are arranged in the raceway at 90 degrees, which can withstand huge radial load, axial load and tilting moment efficiently at the same time.A single set of bearings provides excellent axial/radial stiffness of up to 300 N/μm and effectively resists deformation caused by external loads.Crossed roller bearings with ultra-high precision of P4 or P2 grade are selected, and the radial runout of the inner ring can be controlled within 5μm, which lays a solid mechanical foundation for the overall precision of the platform.Precision assembly process (such as preload control) is crucial to its performance.
3) Precision reduction gear:
Planetary gear structure or precision worm gears are usually used to realize power transmission.In order to achieve the precision target of 15 arc second or even 10 arc second, the gears must reach ISO 6 or higher manufacturing accuracy level, which means that the critical cumulative error of tooth pitch (Fp) needs to be ≤8μm, and the error of tooth shape (fα) needs to be ≤2μm. precision grinding process is the key to ensure this accuracy.In the assembly process, through strict backlash control (usually to achieve micro-preload or zero backlash) and precise meshing center distance adjustment, to ensure smooth, efficient transmission without return error.
4) Drive motor and high-resolution encoder:
Drive motors: mostly use high responsive servo motors (AC or DC).Selection needs to accurately match the load inertia of the platform, the maximum torque required, the maximum speed, especially its control accuracy (resolution) must be matched with the platform's positioning accuracy target (15/10 arc sec).For customized platforms requiring 10 arc sec accuracy, higher performance motors are often required.
5) High Resolution Encoder:
This is the "eyes" of the closed loop control system.To support a positioning accuracy of 15/10 arc sec and excellent repeatability of typically ±5 arc sec, the integrated high-precision rotary encoder (absolute or incremental) must have extremely high resolution (≥20 bits per revolution, i.e. >1,048,576 counts/rev).At the same time, the signals need to be highly stable and resistant to interference (e.g. differential Sin/Cos 1Vpp signals) and may include temperature compensation to ensure the long-term reliability of the feedback data under complex operating conditions and to avoid the accumulation of errors.
2. How to realize the high precision of mechanical rotary platform?
In order to achieve and stably maintain the standard accuracy of 15 arc second, or even 10 arc second customized accuracy, we need to run through the design, manufacturing, assembly and control of the systematic optimization:
Ultra-precision manufacturing of core components: High roundness (<5μm, <2μm for key parts) and high hardness (HRC 58-62) processing of the spindle is the basic guarantee.Gear is the core of transmission accuracy, through precision grinding process to achieve ISO 6 or higher precision (Fp ≤ 8μm, fα ≤ 2μm).Crossed roller bearings are selected from P4/P2 grade ultra-high precision products and precision assembled to ensure that their own errors are minimized and their high rigidity (300 N/μm) is brought into full play.
High-resolution sensing and feedback: The integrated encoder with a single-turn resolution of ≥20 bits (1,048,576 CPR) provides a fine feedback signal with a much higher angular resolution than the target (15 arc sec ≈ 0.00417°, 10 arc sec ≈ 0.00278°), which is a prerequisite for precise position control.Its stability and immunity to interference are equally critical.
Advanced closed-loop control strategy: build a high-performance servo control system based on real-time feedback from high-resolution encoder.Applying advanced algorithms such as feed-forward control, trap filter (to suppress mechanical resonance), friction compensation, adaptive control, etc., it effectively overcomes the system's nonlinear friction, load disturbance and structural vibration, and significantly improves trajectory tracking accuracy and positioning stability.Detailed servo parameter tuning (gain, bandwidth) for specific loads is indispensable.
Structural rigidity and thermal stability design: The platform body adopts rigidity-optimized structures (such as reinforcement bars) and highly rigid materials.Thermal deformation simulation and optimization of key heat sources (such as motors, bearings), and through reasonable heat dissipation design (heat sink, air duct) or the use of low coefficient of thermal expansion materials, to minimize the thermal deformation error caused by temperature rise, to ensure the stability of the accuracy of continuous operation for a long time.