Rotating Workpiece Holding Fixture for Horizontal Mill
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Solution Overview
Problem
Horizontal milling machines with four CNC axes lack the capability to independently rotate workpieces, limiting their ability to mill various surfaces efficiently, and existing five-axis machines are excessively costly.
Innovation Solution
A CNC controlled rotating workpiece holding fixture attached to a tombstone, utilizing a harmonic drive and servo motor for compact stability and low gear ratio, with multiplexing of control signals to reduce wiring requirements, allowing for up to eight fixtures on a single tombstone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large motors are used to position and hold the workpiece, then positioning accuracy and stability are improved, but the space required on the tombstone increases making it impossible to mount multiple fixtures
Solution Approach 1:
The patent replaces traditional large mechanical positioning motors with a harmonic drive mechanism combined with a small servo motor. The harmonic drive provides mechanical advantage through its unique tooth engagement geometry, achieving high reduction ratios (50:1 or higher) in a compact package. This substitution allows the system to maintain position holding stability without requiring large motor sizes, enabling multiple fixtures to be mounted on the tombstone.
Solution Approach 2:
The patent changes the gear ratio parameter by using a harmonic drive with a minimum 50:1 reduction ratio. This high reduction ratio allows a small servo motor to generate sufficient holding torque for workpiece positioning and maintenance, replacing the need for large motors while maintaining the required stability and precision.
2Adaptability or versatility
If multiple rotating workpiece holding fixtures are mounted on a tombstone, then five-axis CNC capability is achieved, but the wiring complexity increases requiring excessive conductors
Solution Approach 1:
The patent implements a multiplexed control system where a single four-conductor cable serves multiple rotating workpiece holding fixtures. The system uses time-division or code-division multiplexing to send control signals to multiple fixtures through shared wiring, allowing one cable to perform the function of many individual cables. This universal approach enables control of multiple fixtures while maintaining simple wiring architecture.
Solution Approach 2:
The patent merges multiple control signal paths into a single multiplexed communication channel. Instead of providing separate wiring for each fixture, the system combines control signals for multiple fixtures into one cable, reducing the total conductor count from potentially 96 conductors to just four conductors while maintaining full control capability over all fixtures.
3Adaptability or versatility
If five-axis horizontal milling machines are used, then multi-surface workpiece milling capability is achieved, but the cost increases by about three times compared to four-axis machines
Solution Approach 1:
The patent segments the five-axis functionality into modular rotating workpiece holding fixtures that can be independently controlled and mounted on a standard tombstone. Rather than purchasing an entirely new five-axis machine, the system divides the capability into separate fixture units that can be added to an existing four-axis horizontal mill, significantly reducing the cost increment compared to buying a complete five-axis machine.
Solution Approach 2:
The patent uses a tombstone as an intermediary platform to mount the rotating workpiece holding fixtures. This intermediary approach allows the integration of five-axis capability through add-on fixtures rather than requiring a complete machine replacement, enabling cost-effective upgrading from four-axis to five-axis functionality.
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
Enables five-axis CNC capability with reduced wiring complexity, providing stable and efficient surface milling without the need for large motors or excessive space, making it a cost-effective solution for horizontal milling machines.
Implementation Method 1
The combination of a low ratio harmonic drive, for example at least 50 to one, and a servo motor provides the necessary position holding in a small envelope.
Data Source
AI summary
A CNC controlled rotating workpiece holding fixture is attached to a tombstone of a horizontal mill. The rotating workpiece holding fixture(s) allows workpieces to be independently rotated to allow milling of various surface of the workpiece thereby providing a five axis CNC capability. As many as eight rotating workpiece holding fixtures may be attached to a single tombstone. Each rotating workpiece holding fixture may be formed by a harmonic drive driven by a servo motor which provides a compact configuration and a very low gear ratio in the harmonic drive combined with the inherent braking of the servo motor provides stability. The rotating workpiece holding fixtures may be controlled using existing auxiliary outputs (e.g., M-Codes), present in CNC milling machines. The M-Codes are preferably created by an operator, multiplexed, sent to the tombstone, de-multiplexed, and used to control each rotating workpiece holding fixture.