Concentric Z-theta Table with Nested Motors
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Solution Overview
Problem
The existing Z-theta tables are bulky, prone to positioning errors due to angular offset, have high mass, stability issues due to ball-screw system limitations, and power cable movement during operation, which is problematic for clean-room applications.
Innovation Solution
A compact Z-theta table design using two substantially concentric rotary motors with a ball-screw system and a single bearing to support the load, where the motor power cables remain fixed, and angular encoders ensure precise positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two stacked circular motors are used to achieve Z-axis linear displacement and angular positioning, then the table can perform both movements independently, but the table height becomes relatively significant and the mass becomes relatively high
Solution Approach 1:
The patent applies nesting by placing the first rotor (with threaded portion) inside the second stator, and the second rotor inside the first stator. This nested configuration allows both motors to occupy overlapping spatial volumes, dramatically reducing the overall table height while maintaining independent control of both Z-axis and angular movements through the ball-screw system and direct rotational drive respectively
2Ease of operation
If the upper motor stator undergoes vertical displacement to enable linear movement control, then the table can achieve Z-axis positioning, but the power cable of the upper motor undergoes movement which is detrimental for clean-room applications
Solution Approach 1:
The patent extracts the linear motion function from the motor stator itself and transfers it to a separate ball-screw mechanism. The first stator remains fixed while the first rotor rotates to drive the ball-screw system, which in turn moves the intermediate piece and table bed along the Z-axis. This separation allows the power cable connected to the first motor to remain stationary while still achieving precise Z-axis positioning through the mechanical transmission system
3Volume of moving object
If a ball-screw system with small diameter is used between the two motors, then the table structure can be compact, but the load capacity is limited and stability is reduced
Solution Approach 1:
The patent resolves the contradiction between compactness and load capacity by transitioning from a single-dimension small-diameter ball-screw to a multi-dimensional solution: the ball-screw system operates in the radial plane while the load is supported by bearings in the axial direction. The first bearing supports radial loads and the second bearing supports axial loads, creating a multi-axis load distribution system that maintains compact dimensions while significantly increasing both load capacity and stability
4Ease of operation
If the load is supported by the fixed lower stator through two bearings or ball bearings, then the table can be activated, but the rigidity and stability are impeded and the Z-θ table base may tilt under decentered load
Solution Approach 1:
The patent inverts the traditional support arrangement by making the outer second stator fixed and the inner first stator movable through the ball-screw mechanism. The load is supported by the fixed outer stator through the second bearing, providing a stable, rigid foundation. The first bearing supports the movable inner components. This inversion creates a more stable structure where the fixed outer stator acts as a rigid reaction member, preventing base tilt under decentered loads while still enabling smooth table activation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves high stability, reduced size, and precise positioning with improved load capacity and rigidity, eliminating the need for a vertical encoder and minimizing the risk of tilting.
Implementation Method 1
One of the two rotors comprises a first cylindrical portion that is threaded and the other has Z-axis linear guide means. The Z-θ table according to the invention also comprises an intermediate piece supporting the table bed and having, on the one hand, a second cylindrical portion that is threaded and, on the other hand, sliding means associated with said guide means to enable displacement of said intermediary piece along the Z axis, said first and second cylindrical portions together forming a ball-screw system.
Implementation Method 2
Measurement of table position occurs by means of two angular encoders associated respectively with the two rotors, each of which has a circular scale.
Data Source
Figure 1
Figure 2
AI summary
The Z-θ table comprises a bed (48) capable of undergoing linear displacement along the Z axis and angular positioning. This table comprises two rotary motors (4, 6) arranged in a substantially concentric manner with two fixed stators (8, 22). The interior rotor (10) comprises means for guiding an intermediary piece (46) along the Z axis and the exterior rotor (24) comprises a threaded portion (44) defining a nut associated with a threaded portion (50) of an intermediary part (46) arranged between the two rotors. The exterior rotor and the intermediary piece define a ball-screw system. Each of the two rotors is associated with an angular displacement sensor (38, 40) for the precise determination of their angular position.